Sports nutrition

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Sports nutrition is the study and practice of nutrition and diet with regards to improving anyone's
athletic performance. Nutrition is an important part of many sports training regimens, being popular
in strength sports (such as weightlifting and bodybuilding) and endurance sports
(e.g. cycling, running, swimming, rowing). Sports Nutrition focuses its studies on the type, as well as
the quantity of fluids and food taken by an athlete. In addition, it deals with the consumption of
nutrients such as vitamins, minerals, supplements and organic substances that
include carbohydrates, proteins and fats.

Contents

 1Supplements
o 1.1Energy supplements
o 1.2Recovery supplements
o 1.3Performance-enhancing supplements
 2Factors influencing nutritional requirements
o 2.1Anaerobic exercise
 3See also
 4References
 5External links

Supplements[edit]
Dietary supplements contain one or more dietary ingredients (including vitamins; minerals; amino
acids; herbs or other botanicals; and other substances) or their constituents is intended to be taken
by mouth as a pill, capsule, tablet, or liquid.[1] Athletes may choose to consider taking dietary
supplements to assist in improving their athletic performance.[2] There are many other supplements
out there that include performance enhancing supplements (steroids, blood doping, creatine, human
growth hormone), energy supplements (caffeine), and supplements that aid in recovery (protein,
BCAAs).
Energy supplements[edit]
Athletes sometimes turn to energy supplements to increase their ability to exercise more often.
Common supplements to increase an athlete's energy include: Caffeine, Guarana, Vitamin B12, and
Asian ginseng.[3] Caffeine, a common energy supplement, can be found in many different forms such
as pills, tablets or capsules, and can also be found in common foods, such as coffee and tea.
Caffeine is used to improve energy and increases metabolism. Guarana is another supplement that
athletes take to enhance their athletic ability, it is frequently used for weight loss and as an energy
supplement.[4]
A 2009 study from the University of Texas reports that caffeinated energy drinks decrease sporting
performance. They found that after drinking an energy drink, 83% of participants improved their
physical activity parameters by an average of 4.7%. This was attributed to the effects of caffeine,
sucrose and Vitamin B in the drink - however scientific consensus does not support the efficacy of
using Vitamin B as a performance enhancer. To explain the performance improvement the writers
report an increase in blood levels of epinephrine, norepinephrine and beta-Endorphin. The
adenosine receptor antagonism of caffeine accounts for the first two,[5][circular reference] while the latter is
accounted for by the Neurobiological effects of physical exercise.[6]
Caffeine has been around since the 1900s and became popularly used in the 1970s when its power
of masking fatigue became highly recognized.[7] Similarly, the caffeine found in energy drinks and
coffee shows an increased reaction performance and feelings of energy, focus and alertness in
quickness and reaction anaerobic power tests. In other words, consuming an energy drink or any
drink with caffeine increases short time/rapid exercise performance (like short full-speed sprints and
heavy power weight lifting).[8] Caffeine is chemically similar to adenosine, a type of sugar that helps
in the regulation of important body processes, including the firing of neurotransmitters. Caffeine
takes the place of adenosine in your brain, attaching itself to the same neural receptors affected by
adenosine, and causing your neurons to fire more rapidly, hence caffeine's stimulating effects.[9]
Carbohydrates are also a very common form of energy supplements, as all sugars are
carbohydrates. Products like Gatorade and Powerade are formulated with simple sugars such as
sucrose and dextrose. Carbohydrates are necessary as they maintain blood glucose levels and
restore muscle glycogen levels.[10]
Recovery supplements[edit]
Common supplements to help athletes recover from exercising include protein and amino
acid supplements. The main use for athletes to take dietary proteins are for hormones, oxygen
transport, cellular repair, enzymes and conversion to fuel.[11] The intake of protein is a part of the
nutrient requirements for the normal athlete and is an important component of exercise training. In
addition, it aids in performance and recovery. Dietary protein intake for well-trained athletes should
occur before, during and after physical activity as it is advantageous in gaining muscle mass and
strength.[12] However, if too much protein and amino acid supplements is consumed it can be more
harmful to the body than it is beneficial; health risks include: dehydration, gout, calcium loss, liver,
renal damage, diarrhea, bloating, and water loss.[11] A bountiful protein diet must be paired with a
healthy, well-rounded meal plan and regular resistance exercise. Characteristics of this particular
diet include the type of exercise, intensity, duration and carbohydrate values of diet.[13] The most
effective way to secure the natural nutrients required by the body for optimum health and
physiological performance is by consuming vitamins, minerals, proteins, fats, sugars and
carbohydrates, which can be procured from fresh fruits and vegetables.[7]
Post-exercise nutrition is an important factor in a nutrition plan for athletes as it pertains to the
recovery of the body. Traditionally, sports drinks such as Gatorade and Powerade, are consumed
during and after exercise because they effectively rehydrate the body by refueling the body with
minerals and electrolytes. Electrolytes regulate the bodies nerve and muscle function, blood pH,
blood pressure, and the rebuilding of damaged tissue.[14] These types of drink are commonly made of
glucose and sucrose in water and has been seen to improve the football players' performance.[7]
A substitute for sports drinks is milk, which contains many electrolytes, nutrients and other elements
that help to make it an effective post-exercise beverage.[15] It is true that milk helps replace fluids and
electrolytes lost after the athlete has worked out. A recovery drink is supposed to replenish the sugar
lost, and help recover the muscles to be able to workout at full intensity by the next time they
workout. When compared to plain water or sports drinks, research supported by the Dairy and
Nutrition Council suggests that chocolate milk is more effective at replacing fluids lost through sweat
and maintaining normal body fluid levels. Athletes drinking chocolate milk following exercise-induced
dehydration had fluid levels about 2 percent higher (on initial body mass) than those using other
post-exercise recovery beverages. These results allowed for prolonged performance, especially in
repeated bouts of exercise or training.[16]
Performance-enhancing supplements[edit]
In the extreme case of performance-enhancing supplements, athletes, particularly bodybuilders may
choose to use illegal substances such as anabolic steroids. These compounds which are related to
the hormone testosterone, can quickly build mass and strength, but have many adverse effects such
as high blood pressure and negative gender specific effects. Blood doping, another illegal ergogenic,
was discovered in the 1940s when it was used by World War II pilots.[7] Blood doping also known as
blood transfusions, increases oxygen delivery to exercising tissues and has been demonstrated to
improve performance in endurance sports, such as long-distance cycling.[17]

An assortment of supplements.

The supplement, Creatine, may be helpful for well-trained athletes to increase exercise performance
and strength in relation with their dietary regimen.[13] The substance glutamine, found in whey fiber
supplements, is the most abundant free amino acid found in the human body.[18] It is considered that
glutamine may have a possible role in stimulated anabolic processes such as muscle glycogen and
protein synthesis, for well-trained and well-nourished athletes.[18] Other popular studies done on
supplements include androstenedione, chromium, and ephedra. The findings show that there are no
substantial benefits from the extra intake of these supplements, yet higher health risks and costs.[13]

Factors influencing nutritional requirements[edit]

Differing conditions and objectives suggest the need for athletes to ensure that their sports
nutritional approach is appropriate for their situation. Factors that may affect an athlete's nutritional
needs include type of activity (aerobic vs. anaerobic), gender, weight, height, body mass index,
workout or activity stage (pre-workout, intro-workout, recovery), and time of day (e.g. some nutrients
are utilized by the body more effectively during sleep than while awake).Most culprits that get in the
way of performance are fatigue, injury and soreness. A proper diet will reduce these disturbances in
performance. The key to a proper diet is to get a variety of food, and to consume all the macro-
nutrients, vitamins, and minerals needed. According to Eblere's article (2008), it is ideal to choose
raw foods, for example unprocessed foods such as oranges instead of orange juice. Eating foods
that are natural means the athlete is getting the most nutritional value out of the food. When foods
are processed, the nutritional value is normally reduced.[19]
Anaerobic exercise[edit]
Weightlifting is an anaerobic exercise

During anaerobic exercise, the process of glycolysis breaks down the sugars from carbohydrates for
energy without the use of oxygen. This type of exercise occurs in physical activity such as power
sprints, strength resistances and quick explosive movement where the muscles are being used for
power and speed, with short-time energy use. After this type of exercise, there is a need to
refill glycogen storage sites in the body (the long simple sugar chains in the body that store energy),
although they are not likely fully depleted.
To compensate for this glycogen reduction, athletes will often take in large amounts of
carbohydrates, immediately following their exercise. Typically, high-glycemic-index carbohydrates
are preferred for their ability to rapidly raise blood glucose levels.For the purpose of protein
synthesis, protein or individual amino acids are ingested as well. Branched-chain amino acids are
important since they are most responsible for the synthesis of protein. According to Lemon et al.
(1995) female endurance runners have the hardest time getting enough protein in their diet.
Endurance athletes in general need more protein in their diet than the sedentary person.Research
has shown that endurance athletes are recommended to have 1.2 to 1.4 g of protein per kg of body
weight in order to repair damaged tissue. If the athlete consumes too few calories for the body's
needs, lean tissue will be broken down for energy and repair. Protein deficiency can cause many
problems such as early and extreme fatigue, particularly long recovery, and poor wound healing.
Complete proteins such as meat, eggs, and soy provide the athlete with all essential amino acids for
synthesizing new tissues. However, vegetarian and vegan athletes frequently combine legumes with
a whole grain to provide the body with a complete protein across the day's food intake.[20] A popular
combination being rice and beans.[21]
Spada's research on endurance sports nutrition (2000) and where the types of carbohydrates come
from will be explained. He advises for carbohydrates to be unprocessed and/or whole grains for
optimal performance while training. These carbohydrates offer the most fuel, nutritional value, and
satiety. Fruits and vegetables contribute important carbohydrate foundation for an athlete's diet.
They provide vitamins and minerals that are lost through exercise and later needed to be
replenished. Both fruits and vegetables improve healing, aid in recovery, and reduce risks of cancer,
high blood pressure, and constipation. Vegetables offer a little more nutritional value than fruits for
the amount of calories, therefore an athlete should strive to eat more vegetables than fruits. Dark-
colored vegetables usually have more nutritional value than pale colored ones.(add info) A general
rule is the darker the color the more nutrient dense it is. Like all foods, it is very important to have a
variety. To get the most nutritional value out of fruits and vegetables it is important to eat them in
their natural, unprocessed form with no other nutrient (sugar) added.[22]
Often in the continuation of this anaerobic exercise, the product from this metabolic mechanism
builds up in what is called lactic acid fermentation. Lactate is produced more quickly than it is being
removed and it serves to regenerate NAD+ cells on where it's needed. During intense exercise when
oxygen is not being used, a high amount of ATP is produced and pH levels fall causing acidosis or
more specifically lactic acidosis. Lactic acid build up can be treated by staying well-hydrated
throughout and especially after the workout, having an efficient cool down routine and good post-
workout stretching.[23]
Intense activity can cause significant and permanent damage to bodily tissues. In order to repair,
vitamin E and other antioxidants are needed to protect muscle damage. Oxidation damage and
muscle tissue breakdown happens during endurance running so athletes need to eat foods high in
protein in order to repair these muscle tissues. It is important for female endurance runners to
consume proper nutrients in their diet that will repair, fuel, and minimize fatigue and injury. To keep a
female runner's body performing at its best, the ten nutrients need to be included in their diets.[24]

See also[edit]
 Category:Dietary supplements
 Energy bar
 Protein
 Sports drink
 Multivitamin
 Bodybuilding
 Bodybuilding supplements
 High-protein diet
 Sports nutritionist

References[edit]
1. ^ "Background Information: Dietary Supplements — Health Professional Fact Sheet." U.S National
Library of Medicine. U.S. National Library of Medicine, 24 June 2011. Web. 04 Nov. 2016.
2. ^ Maughan, Ronald J., ed. "Sports Nutrition: What Is It?" Journal of Nutrition & Physical Activity 17
(2001). 2001. Elsevier Science Inc. 25 Mar. 2009.
3. ^ "Energy Boosters: Can Supplements and Vitamins Help?". WebMD. Retrieved 2017-05-18.
4. ^ "GUARANA: Uses, Side Effects, Interactions and Warnings - WebMD". www.webmd.com.
Retrieved 2017-05-18.
5. ^ Caffeine#Pharmacodynamics
6. ^ "Improved Cycling Time-Trial Performance After Ingestion of a Caffeine Energy Drink." International
Journal of Sport Nutrition and Exercise Metabolism 19 (February 2009): 61-78.
7. ^ Jump up to:a b c d Applegate, Elizabeth A., and Louis E. Grivetti. "Search for the Competitive Edge: A
History of Dietary Fads and Supplements." The Journal of Nutrition (1997): 869S-73S. The Journal of
Nutrition. American Society for Nutritional Sciences. 1 Apr. 2009 <jn.nutrition.org>.
8. ^ Hoffman, Jay R., Jie Kang, Nicholas A. Ratamess, Mattan W. Hoffman, Christopher P. Tranchina,
and Avery D. Faigenbaum. "Examination of a pre-exercise, high energy supplement on exercise
performance." Journal of the International Society of Sports Nutrition 6 (2009). Journal of the
International Society of Sports Nutrition. 6 Jan. 2009. BioMed Central Ltd. 25 Mar. 2009
9. ^ "The Side Effects of Caffeine / Nutrition / Healthy Eating." The Side Effects of Caffeine / Nutrition /
Healthy Eating. N.p., n.d. Web. 07 Nov. 2016.
10. ^ Nancy R. Rodriguez; Nancy M. DiMarco; Susie Langley (1 March 2010). "Nutrition and Athletic
Performance". Medscape. Retrieved 2019-02-15.
11. ^ Jump up to:a b Wilson, Lawrence, Dr. "THE IMPORTANCE OF PROTEIN." THE IMPORTANCE OF
PROTEIN. N.p., Dec. 2015. Web. 05 Nov. 2016.
12. ^ Campbell, Bill, Richard B. Kreider, Tim Ziegenfuss, Paul La Bounty, Mike Roberts, Darren Burke,
Jamie Landis, Hector Lopez, and Jose Antonio. "International Society of Sports Nutrition position
stand: protein and exercise." Journal of the International Society of Sports Nutrition 4 (2007). Journal
 of the International Society of Sports Nutrition. 26 Sept. 2007. BioMed Central Ltd. 25 Mar. 2009
<http://www.jissn.com/content/4/1/8>.
13. ^ Jump up to:a b c Lawrence, Marvin E., and Donald F. Kirby. "Nutrition and Sports Supplements Fact
or Fiction." Journal of Clinical Gastroenterology 35 (2002): 299-306. Journal of Clinical
Gastroenterology. 2002. Lippincott Williams & Wilkins. 25 Mar. 2009 <journals.lww.com/jcge/>.
14. ^ Nordqvist, Christian. "What Are Electrolytes? What Causes Electrolyte Imbalance?" Medical News
Today. MediLexicon International, 24 May 2016. Web. 07 Nov. 2016.
15. ^ Busch, Sandi. "Does Milk Contain Electrolytes?". LIVESTRONG.COM. Retrieved 2017-05-18.
16. ^ Stager, Joel M., et al. "Chocolate Milk as a Post-Exercise Recovery Aid." International Journal of
Sport Nutrition and Exercise Metabolism.
2006.<https://www.researchgate.net/publication/7103747_Chocolate_Milk_as_a_Post-
Exercise_Recovery_Aid>.
17. ^ Jenkinson, David M., DO, and Allison J. Harbert, MD. "Supplements and Sports." American Family
Physician. N.p., 1 Nov. 2008. Web. 4 Nov. 2016.
18. ^ Jump up to:a b Gleeson, Michael. "Dosing and Efficacy of Glutamine Supplementation." The Journal
of Nutrition (2008): 2045S-049S. Nov. 2008. 25 Mar. 2009 <jn.nutrition.org>.
19. ^ Eberle, S. G. "Endurance sports nutrition". Fitness Magazine. 24 (6): 25.
20. ^ Jurek, Scott (2012). Eat and Run. London: Bloomsbury.
21. ^ Lemon P. "Do athletes need more dietary protein and amino acids?". International Journal of Sports
Nutrition. 5: 39–61.
22. ^ Spada R. "Endurance sports nutrition". Journal of Sports Medicine and Physical Fitness. 40 (4):
381–382.
23. ^ Delamere, Nicholas, and Claudia Stanescu. "Muscle Energetics." Physiology 201. University of
Arizona, Tucson. 25, 27, 29 Mar. 2009.
24. ^ Rokitzki L. "Alpha-tocopherol supplementation in racing cyclist during extreme endurance
training". International Journal of Sports Nutrition. 4 (3): 253–64. doi:10.1123/ijsn.4.3.253.

External links[edit]
Wikimedia Commons has
media related to Sports
nutrition.

 The International Society of Sports Nutrition

 Journal of Sports Nutrition
 Tips to good hydration during physical activity
 Nutrition for Athletes of all ages, contains many good links.
 Energy bar
From Wikipedia, the free encyclopedia
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For similar types of cereal bars, see granola bar.

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This article possibly contains original research. (March 2011)

A HOOAH! energy bar provided by the United States Army in its MREs

Energy bars are supplemental bars containing cereals and other high energy foods targeted at
people who require quick energy but do not have time for a meal.

Contents

 1Nutrition
 2Usage
 3See also
 4References

Nutrition[edit]
Energy in food comes from three sources: fat, protein, and carbohydrates. A typical energy bar
weighs between 45 and 80 g and is likely to supply about 200–300 Cal (840–1,300 kJ), 3–9 g of fat,
7–15 g of protein, and 20–40 g of carbohydrates.[1] In order to provide energy quickly, most of the
carbohydrates are various types of sugars like fructose, glucose, maltodextrin and others in various
ratios, combined with complex carbohydrate sources like oats and barley. Proteins come mostly in
the form of fast digesting whey protein. Energy bars generally don't contain sugar alcohols, since
these bars, due to type of carbohydrate content, don't require low calorie sweeteners to improve
their taste. Fats in energy bars are kept to minimum and their main sources are often cocoa
butter and dark chocolate.[citation needed]

Usage[edit]
Energy bars are used as energy source during athletic events like marathon, triathlon and other
events and outdoor activities, where energy expenditure is high, for longer period of time.
Protein
From Wikipedia, the free encyclopedia
Jump to navigationJump to search
This article is about a class of molecules. For protein as a nutrient, see protein (nutrient). For other
uses, see protein (disambiguation).

A representation of the 3D structure of the protein myoglobin showing turquoise α-helices. This protein was the
first to have its structure solved by X-ray crystallography. Towards the right-center among the coils, a prosthetic
group called a heme group(shown in gray) with a bound oxygen molecule (red).

Proteins are large biomolecules, or macromolecules, consisting of one or more long chains
of amino acid residues. Proteins perform a vast array of functions within organisms,
including catalysing metabolic reactions, DNA replication, responding to stimuli, providing structure
to cells and organisms, and transporting molecules from one location to another. Proteins differ from
one another primarily in their sequence of amino acids, which is dictated by the nucleotide
sequence of their genes, and which usually results in protein foldinginto a specific three-dimensional
structure that determines its activity.
A linear chain of amino acid residues is called a polypeptide. A protein contains at least one long
polypeptide. Short polypeptides, containing less than 20–30 residues, are rarely considered to be
proteins and are commonly called peptides, or sometimes oligopeptides. The individual amino acid
residues are bonded together by peptide bonds and adjacent amino acid residues. The sequence of
amino acid residues in a protein is defined by the sequence of a gene, which is encoded in
the genetic code. In general, the genetic code specifies 20 standard amino acids; however, in certain
organisms the genetic code can include selenocysteine and—in certain archaea—pyrrolysine.
Shortly after or even during synthesis, the residues in a protein are often chemically modified
by post-translational modification, which alters the physical and chemical properties, folding, stability,
activity, and ultimately, the function of the proteins. Sometimes proteins have non-peptide groups
attached, which can be called prosthetic groups or cofactors. Proteins can also work together to
achieve a particular function, and they often associate to form stable protein complexes.
Once formed, proteins only exist for a certain period and are then degraded and recycled by the
cell's machinery through the process of protein turnover. A protein's lifespan is measured in terms of
its half-life and covers a wide range. They can exist for minutes or years with an average lifespan of
1–2 days in mammalian cells. Abnormal or misfolded proteins are degraded more rapidly either due
to being targeted for destruction or due to being unstable.
Like other biological macromolecules such as polysaccharides and nucleic acids, proteins are
essential parts of organisms and participate in virtually every process within cells. Many proteins
 are enzymes that catalyse biochemical reactions and are vital to metabolism. Proteins also have
structural or mechanical functions, such as actin and myosin in muscle and the proteins in
the cytoskeleton, which form a system of scaffolding that maintains cell shape. Other proteins are
important in cell signaling, immune responses, cell adhesion, and the cell cycle. In animals, proteins
are needed in the diet to provide the essential amino acids that cannot
be synthesized. Digestion breaks the proteins down for use in the metabolism.
Proteins may be purified from other cellular components using a variety of techniques such
as ultracentrifugation, precipitation, electrophoresis, and chromatography; the advent of genetic
engineering has made possible a number of methods to facilitate purification. Methods commonly
used to study protein structure and function include immunohistochemistry, site-directed
mutagenesis, X-ray crystallography, nuclear magnetic resonance and mass spectrometry.

Contents

 1Biochemistry
o 1.1Interactions
o 1.2Abundance in cells
 2Synthesis
o 2.1Biosynthesis
o 2.2Chemical synthesis
 3Structure
o 3.1Protein domains
o 3.2Sequence motif
 4Cellular functions
o 4.1Enzymes
o 4.2Cell signaling and ligand binding
o 4.3Structural proteins
 5Methods of study
o 5.1Protein purification
o 5.2Cellular localization
o 5.3Proteomics
o 5.4Bioinformatics
o 5.5Structure determination
o 5.6Structure prediction and simulation
 5.6.1Protein disorder and unstructure prediction
 6Nutrition
 7History and etymology
 8See also
 9References
 10Textbooks
 11External links
o 11.1Databases and projects
o 11.2Tutorials and educational websites

Biochemistry
Chemical structure of the peptide bond (bottom) and the three-dimensional structure of a peptide bond between
an alanine and an adjacent amino acid (top/inset). The bond itself is made of the CHONelements.

Resonance structures of the peptide bond that links individual amino acids to form a protein polymer

Main articles: Biochemistry, Amino acid, and Peptide bond

Most proteins consist of linear polymers built from series of up to 20 different L-α- amino acids.
All proteinogenic amino acids possess common structural features, including an α-carbon to which
an amino group, a carboxyl group, and a variable side chain are bonded. Only proline differs from
this basic structure as it contains an unusual ring to the N-end amine group, which forces the CO–
NH amide moiety into a fixed conformation.[1] The side chains of the standard amino acids, detailed
in the list of standard amino acids, have a great variety of chemical structures and properties; it is
the combined effect of all of the amino acid side chains in a protein that ultimately determines its
three-dimensional structure and its chemical reactivity.[2] The amino acids in a polypeptide chain are
linked by peptide bonds. Once linked in the protein chain, an individual amino acid is called
a residue, and the linked series of carbon, nitrogen, and oxygen atoms are known as the main
chain or protein backbone.[3]
The peptide bond has two resonance forms that contribute some double-bond character and inhibit
rotation around its axis, so that the alpha carbons are roughly coplanar. The other two dihedral
angles in the peptide bond determine the local shape assumed by the protein backbone.[4] The end
with a free amino group is known as the N-terminus or amino terminus, whereas the end of the
protein with a free carboxyl group is known as the C-terminus or carboxy terminus (the sequence of
the protein is written from N-terminus to C-terminus, from left to right).
The words protein, polypeptide, and peptide are a little ambiguous and can overlap in
meaning. Protein is generally used to refer to the complete biological molecule in a
stable conformation, whereas peptide is generally reserved for a short amino acid oligomers often
lacking a stable three-dimensional structure. However, the boundary between the two is not well
defined and usually lies near 20–30 residues.[5] Polypeptide can refer to any single linear chain of
amino acids, usually regardless of length, but often implies an absence of a defined conformation.
Interactions
Proteins can interact with many types of molecules, including with other proteins, with lipids, with
carboyhydrates, and with DNA.[6][7][8][9]
Abundance in cells
It has been estimated that average-sized bacteria contain about 2 million proteins per cell (e.g. E.
coli and Staphylococcus aureus). Smaller bacteria, such as Mycoplasma or spirochetes contain
fewer molecules, on the order of 50,000 to 1 million. By contrast, eukaryotic cells are larger and thus
contain much more protein. For instance, yeast cells have been estimated to contain about 50
million proteins and human cells on the order of 1 to 3 billion.[10] The concentration of individual
protein copies ranges from a few molecules per cell up to 20 million.[11] Not all genes coding proteins
are expressed in most cells and their number depends on, for example, cell type and external
stimuli. For instance, of the 20,000 or so proteins encoded by the human genome, only 6,000 are
detected in lymphoblastoid cells.[12] Moreover, the number of proteins the genomeencodes correlates
well with the organism complexity. Eukaryotes have 15,000, bacteria have 3,200, archaea have
2,400, and viruses have 42 proteins on average coded in their respective genomes.[13]

Synthesis
Biosynthesis

A ribosome produces a protein using mRNA as template

The DNA sequence of a gene encodes the amino acid sequence of a protein

Main article: Protein biosynthesis

Proteins are assembled from amino acids using information encoded in genes. Each protein has its
own unique amino acid sequence that is specified by the nucleotide sequence of the gene encoding
this protein. The genetic code is a set of three-nucleotide sets called codons and each three-
nucleotide combination designates an amino acid, for example AUG (adenine-uracil-guanine) is the
code for methionine. Because DNA contains four nucleotides, the total number of possible codons is
64; hence, there is some redundancy in the genetic code, with some amino acids specified by more
than one codon.[14] Genes encoded in DNA are first transcribed into pre-messenger RNA (mRNA) by
proteins such as RNA polymerase. Most organisms then process the pre-mRNA (also known as
a primary transcript) using various forms of Post-transcriptional modification to form the mature
mRNA, which is then used as a template for protein synthesis by the ribosome. In prokaryotes the
mRNA may either be used as soon as it is produced, or be bound by a ribosome after having moved
away from the nucleoid. In contrast, eukaryotes make mRNA in the cell nucleus and
then translocate it across the nuclear membrane into the cytoplasm, where protein synthesis then
takes place. The rate of protein synthesis is higher in prokaryotes than eukaryotes and can reach up
to 20 amino acids per second.[15]
The process of synthesizing a protein from an mRNA template is known as translation. The mRNA is
loaded onto the ribosome and is read three nucleotides at a time by matching each codon to its base
pairing anticodon located on a transfer RNA molecule, which carries the amino acid corresponding
to the codon it recognizes. The enzyme aminoacyl tRNA synthetase "charges" the tRNA molecules
with the correct amino acids. The growing polypeptide is often termed the nascent chain. Proteins
are always biosynthesized from N-terminus to C-terminus.[14]
The size of a synthesized protein can be measured by the number of amino acids it contains and by
its total molecular mass, which is normally reported in units of daltons (synonymous with atomic
mass units), or the derivative unit kilodalton (kDa). The average size of a protein increases from
Archaea to Bacteria to Eukaryote (283, 311, 438 residues and 31, 34, 49 kDa respecitvely) due to a
bigger number of protein domains constituting proteins in higher organisms.[13] For
instance, yeast proteins are on average 466 amino acids long and 53 kDa in mass.[5] The largest
known proteins are the titins, a component of the muscle sarcomere, with a molecular mass of
almost 3,000 kDa and a total length of almost 27,000 amino acids.[16]
Chemical synthesis
Main article: Peptide synthesis
Short proteins can also be synthesized chemically by a family of methods known as peptide
synthesis, which rely on organic synthesis techniques such as chemical ligation to produce peptides
in high yield.[17] Chemical synthesis allows for the introduction of non-natural amino acids into
polypeptide chains, such as attachment of fluorescent probes to amino acid side chains.[18] These
methods are useful in laboratory biochemistry and cell biology, though generally not for commercial
applications. Chemical synthesis is inefficient for polypeptides longer than about 300 amino acids,
and the synthesized proteins may not readily assume their native tertiary structure. Most chemical
synthesis methods proceed from C-terminus to N-terminus, opposite the biological reaction.[19]

Structure

The crystal structure of the chaperonin, a huge protein complex. A single protein subunit is highlighted.
Chaperonins assist protein folding.

Three possible representations of the three-dimensional structure of the protein triose phosphate
isomerase. Left: All-atom representation colored by atom type. Middle: Simplified representation illustrating the
backbone conformation, colored by secondary structure. Right: Solvent-accessible surface representation
colored by residue type (acidic residues red, basic residues blue, polar residues green, nonpolar residues
white).

Main article: Protein structure

Further information: Protein structure prediction
Most proteins fold into unique 3-dimensional structures. The shape into which a protein naturally
folds is known as its native conformation.[20] Although many proteins can fold unassisted, simply
through the chemical properties of their amino acids, others require the aid of
molecular chaperones to fold into their native states.[21] Biochemists often refer to four distinct
aspects of a protein's structure:[22]

 Primary structure: the amino acid sequence. A protein is a polyamide.

 Secondary structure: regularly repeating local structures stabilized by hydrogen bonds. The
most common examples are the α-helix, β-sheet and turns. Because secondary structures are
local, many regions of different secondary structure can be present in the same protein
molecule.
 Tertiary structure: the overall shape of a single protein molecule; the spatial relationship of the
secondary structures to one another. Tertiary structure is generally stabilized by nonlocal
interactions, most commonly the formation of a hydrophobic core, but also through salt bridges,
hydrogen bonds, disulfide bonds, and even posttranslational modifications. The term "tertiary
structure" is often used as synonymous with the term fold. The tertiary structure is what controls
the basic function of the protein.
 Quaternary structure: the structure formed by several protein molecules (polypeptide chains),
usually called protein subunits in this context, which function as a single protein complex.
Proteins are not entirely rigid molecules. In addition to these levels of structure, proteins may shift
between several related structures while they perform their functions. In the context of these
functional rearrangements, these tertiary or quaternary structures are usually referred to as
"conformations", and transitions between them are called conformational changes. Such changes
are often induced by the binding of a substrate molecule to an enzyme's active site, or the physical
region of the protein that participates in chemical catalysis. In solution proteins also undergo
variation in structure through thermal vibration and the collision with other molecules.[23]

Molecular surface of several proteins showing their comparative sizes. From left to right are: immunoglobulin
G (IgG, an antibody), hemoglobin, insulin (a hormone), adenylate kinase (an enzyme), and glutamine
synthetase (an enzyme).

Proteins can be informally divided into three main classes, which correlate with typical tertiary
structures: globular proteins, fibrous proteins, and membrane proteins. Almost all globular proteins
are soluble and many are enzymes. Fibrous proteins are often structural, such as collagen, the
major component of connective tissue, or keratin, the protein component of hair and nails.
Membrane proteins often serve as receptors or provide channels for polar or charged molecules to
pass through the cell membrane.[24]
A special case of intramolecular hydrogen bonds within proteins, poorly shielded from water attack
and hence promoting their own dehydration, are called dehydrons.[25]
Protein domains
Main article: Protein domain
Many proteins are composed of several protein domains, i.e. segments of a protein that fold into
distinct structural units. Domains usually also have specific functions, such as enzymatic activities
(e.g. kinase) or they serve as binding modules (e.g. the SH3 domain binds to proline-rich sequences
in other proteins).
Sequence motif
Short amino acid sequences within proteins often act as recognition sites for other proteins.[26] For
instance, SH3 domains typically bind to short PxxP motifs (i.e. 2 prolines[P], separated by 2
unspecified amino acids [x], although the surrounding amino acids may determine the exact binding
specificity). A large number of such motifs has been collected in the Eukaryotic Linear Motif (ELM)
database.

Cellular functions
Proteins are the chief actors within the cell, said to be carrying out the duties specified by the
information encoded in genes.[5] With the exception of certain types of RNA, most other biological
molecules are relatively inert elements upon which proteins act. Proteins make up half the dry weight
of an Escherichia coli cell, whereas other macromolecules such as DNA and RNA make up only 3%
and 20%, respectively.[27] The set of proteins expressed in a particular cell or cell type is known as
its proteome.

The enzyme hexokinase is shown as a conventional ball-and-stick molecular model. To scale in the top right-
hand corner are two of its substrates, ATP and glucose.

The chief characteristic of proteins that also allows their diverse set of functions is their ability to bind
other molecules specifically and tightly. The region of the protein responsible for binding another
molecule is known as the binding site and is often a depression or "pocket" on the molecular surface.
This binding ability is mediated by the tertiary structure of the protein, which defines the binding site
pocket, and by the chemical properties of the surrounding amino acids' side chains. Protein binding
can be extraordinarily tight and specific; for example, the ribonuclease inhibitor protein binds to
human angiogenin with a sub-femtomolar dissociation constant(<10−15 M) but does not bind at all to
its amphibian homolog onconase (>1 M). Extremely minor chemical changes such as the addition of
a single methyl group to a binding partner can sometimes suffice to nearly eliminate binding; for
example, the aminoacyl tRNA synthetase specific to the amino acid valine discriminates against the
very similar side chain of the amino acid isoleucine.[28]
Proteins can bind to other proteins as well as to small-molecule substrates. When proteins bind
specifically to other copies of the same molecule, they can oligomerize to form fibrils; this process
occurs often in structural proteins that consist of globular monomers that self-associate to form rigid
fibers. Protein–protein interactions also regulate enzymatic activity, control progression through
the cell cycle, and allow the assembly of large protein complexes that carry out many closely related
reactions with a common biological function. Proteins can also bind to, or even be integrated into,
cell membranes. The ability of binding partners to induce conformational changes in proteins allows
the construction of enormously complex signaling networks.[29] As interactions between proteins are
reversible, and depend heavily on the availability of different groups of partner proteins to form
aggregates that are capable to carry out discrete sets of function, study of the interactions between
specific proteins is a key to understand important aspects of cellular function, and ultimately the
properties that distinguish particular cell types.[30][31]
Enzymes
Main article: Enzyme
The best-known role of proteins in the cell is as enzymes, which catalyse chemical reactions.
Enzymes are usually highly specific and accelerate only one or a few chemical reactions. Enzymes
carry out most of the reactions involved in metabolism, as well as manipulating DNA in processes
such as DNA replication, DNA repair, and transcription. Some enzymes act on other proteins to add
or remove chemical groups in a process known as posttranslational modification. About 4,000
reactions are known to be catalysed by enzymes.[32] The rate acceleration conferred by enzymatic
catalysis is often enormous—as much as 1017-fold increase in rate over the uncatalysed reaction in
the case of orotate decarboxylase (78 million years without the enzyme, 18 milliseconds with the
enzyme).[33]
The molecules bound and acted upon by enzymes are called substrates. Although enzymes can
consist of hundreds of amino acids, it is usually only a small fraction of the residues that come in
contact with the substrate, and an even smaller fraction—three to four residues on average—that
are directly involved in catalysis.[34] The region of the enzyme that binds the substrate and contains
the catalytic residues is known as the active site.
Dirigent proteins are members of a class of proteins that dictate the stereochemistry of a compound
synthesized by other enzymes.[35]
Cell signaling and ligand binding

Ribbon diagram of a mouse antibody against cholera that binds a carbohydrate antigen

Many proteins are involved in the process of cell signaling and signal transduction. Some proteins,
such as insulin, are extracellular proteins that transmit a signal from the cell in which they were
synthesized to other cells in distant tissues. Others are membrane proteins that act
as receptors whose main function is to bind a signaling molecule and induce a biochemical response
in the cell. Many receptors have a binding site exposed on the cell surface and an effector domain
within the cell, which may have enzymatic activity or may undergo a conformational change detected
by other proteins within the cell.[36]
Antibodies are protein components of an adaptive immune system whose main function is to
bind antigens, or foreign substances in the body, and target them for destruction. Antibodies can
be secreted into the extracellular environment or anchored in the membranes of specialized B
cells known as plasma cells. Whereas enzymes are limited in their binding affinity for their substrates
by the necessity of conducting their reaction, antibodies have no such constraints. An antibody's
binding affinity to its target is extraordinarily high.[37]
Many ligand transport proteins bind particular small biomolecules and transport them to other
locations in the body of a multicellular organism. These proteins must have a high binding affinity
when their ligand is present in high concentrations, but must also release the ligand when it is
present at low concentrations in the target tissues. The canonical example of a ligand-binding
protein is haemoglobin, which transports oxygenfrom the lungs to other organs and tissues in
all vertebrates and has close homologs in every biological kingdom.[38] Lectins are sugar-binding
proteins which are highly specific for their sugar moieties. Lectins typically play a role in
biological recognition phenomena involving cells and proteins.[39] Receptors and hormones are highly
specific binding proteins.
Transmembrane proteins can also serve as ligand transport proteins that alter the permeability of the
cell membrane to small molecules and ions. The membrane alone has a hydrophobic core through
which polar or charged molecules cannot diffuse. Membrane proteins contain internal channels that
allow such molecules to enter and exit the cell. Many ion channel proteins are specialized to select
for only a particular ion; for example, potassium and sodium channels often discriminate for only one
of the two ions.[40]
Structural proteins
Structural proteins confer stiffness and rigidity to otherwise-fluid biological components. Most
structural proteins are fibrous proteins; for example, collagen and elastin are critical components
of connective tissue such as cartilage, and keratin is found in hard or filamentous structures such
as hair, nails, feathers, hooves, and some animal shells.[41] Some globular proteins can also play
structural functions, for example, actin and tubulin are globular and soluble as monomers,
but polymerize to form long, stiff fibers that make up the cytoskeleton, which allows the cell to
maintain its shape and size.
Other proteins that serve structural functions are motor proteins such as myosin, kinesin,
and dynein, which are capable of generating mechanical forces. These proteins are crucial for
cellular motility of single celled organisms and the sperm of many multicellular organisms which
reproduce sexually. They also generate the forces exerted by contracting muscles[42] and play
essential roles in intracellular transport.

Methods of study
Main article: Protein methods
The activities and structures of proteins may be examined in vitro, in vivo, and in silico. In
vitro studies of purified proteins in controlled environments are useful for learning how a protein
carries out its function: for example, enzyme kinetics studies explore the chemical mechanism of an
enzyme's catalytic activity and its relative affinity for various possible substrate molecules. By
contrast, in vivo experiments can provide information about the physiological role of a protein in the
context of a cell or even a whole organism. In silico studies use computational methods to study
proteins.
Protein purification
Main article: Protein purification
To perform in vitro analysis, a protein must be purified away from other cellular components. This
process usually begins with cell lysis, in which a cell's membrane is disrupted and its internal
contents released into a solution known as a crude lysate. The resulting mixture can be purified
using ultracentrifugation, which fractionates the various cellular components into fractions containing
soluble proteins; membrane lipids and proteins; cellular organelles, and nucleic
acids. Precipitation by a method known as salting out can concentrate the proteins from this lysate.
Various types of chromatography are then used to isolate the protein or proteins of interest based on
properties such as molecular weight, net charge and binding affinity.[43] The level of purification can
be monitored using various types of gel electrophoresis if the desired protein's molecular weight
and isoelectric point are known, by spectroscopy if the protein has distinguishable spectroscopic
features, or by enzyme assays if the protein has enzymatic activity. Additionally, proteins can be
isolated according to their charge using electrofocusing.[44]
For natural proteins, a series of purification steps may be necessary to obtain protein sufficiently
pure for laboratory applications. To simplify this process, genetic engineeringis often used to add
chemical features to proteins that make them easier to purify without affecting their structure or
activity. Here, a "tag" consisting of a specific amino acid sequence, often a series
of histidine residues (a "His-tag"), is attached to one terminus of the protein. As a result, when the
lysate is passed over a chromatography column containing nickel, the histidine residues ligate the
nickel and attach to the column while the untagged components of the lysate pass unimpeded. A
number of different tags have been developed to help researchers purify specific proteins from
complex mixtures.[45]
Cellular localization

Proteins in different cellular compartments and structures tagged with green fluorescent protein(here, white)

The study of proteins in vivo is often concerned with the synthesis and localization of the protein
within the cell. Although many intracellular proteins are synthesized in the cytoplasm and
membrane-bound or secreted proteins in the endoplasmic reticulum, the specifics of how proteins
are targeted to specific organelles or cellular structures is often unclear. A useful technique for
assessing cellular localization uses genetic engineering to express in a cell a fusion
protein or chimera consisting of the natural protein of interest linked to a "reporter" such as green
fluorescent protein(GFP).[46] The fused protein's position within the cell can be cleanly and efficiently
visualized using microscopy,[47] as shown in the figure opposite.
Other methods for elucidating the cellular location of proteins requires the use of known
compartmental markers for regions such as the ER, the Golgi, lysosomes or vacuoles, mitochondria,
chloroplasts, plasma membrane, etc. With the use of fluorescently tagged versions of these markers
or of antibodies to known markers, it becomes much simpler to identify the localization of a protein of
interest. For example, indirect immunofluorescence will allow for fluorescence colocalization and
demonstration of location. Fluorescent dyes are used to label cellular compartments for a similar
purpose.[48]
Other possibilities exist, as well. For example, immunohistochemistry usually utilizes an antibody to
one or more proteins of interest that are conjugated to enzymes yielding either luminescent or
chromogenic signals that can be compared between samples, allowing for localization information.
Another applicable technique is cofractionation in sucrose (or other material) gradients
using isopycnic centrifugation.[49] While this technique does not prove colocalization of a
compartment of known density and the protein of interest, it does increase the likelihood, and is
more amenable to large-scale studies.
Finally, the gold-standard method of cellular localization is immunoelectron microscopy. This
technique also uses an antibody to the protein of interest, along with classical electron microscopy
techniques. The sample is prepared for normal electron microscopic examination, and then treated
with an antibody to the protein of interest that is conjugated to an extremely electro-dense material,
usually gold. This allows for the localization of both ultrastructural details as well as the protein of
interest.[50]
Through another genetic engineering application known as site-directed mutagenesis, researchers
can alter the protein sequence and hence its structure, cellular localization, and susceptibility to
regulation. This technique even allows the incorporation of unnatural amino acids into proteins, using
modified tRNAs,[51] and may allow the rational design of new proteins with novel properties.[52]
Proteomics
Main article: Proteomics
The total complement of proteins present at a time in a cell or cell type is known as its proteome,
and the study of such large-scale data sets defines the field of proteomics, named by analogy to the
related field of genomics. Key experimental techniques in proteomics include 2D
electrophoresis,[53] which allows the separation of a large number of proteins, mass
spectrometry,[54] which allows rapid high-throughput identification of proteins and sequencing of
peptides (most often after in-gel digestion), protein microarrays, which allow the detection of the
relative levels of a large number of proteins present in a cell, and two-hybrid screening, which allows
the systematic exploration of protein–protein interactions.[55] The total complement of biologically
possible such interactions is known as the interactome.[56] A systematic attempt to determine the
structures of proteins representing every possible fold is known as structural genomics.[57]
Bioinformatics
Main article: Bioinformatics
A vast array of computational methods have been developed to analyze the structure, function, and
evolution of proteins.
The development of such tools has been driven by the large amount of genomic and proteomic data
available for a variety of organisms, including the human genome. It is simply impossible to study all
proteins experimentally, hence only a few are subjected to laboratory experiments while
computational tools are used to extrapolate to similar proteins. Such homologous proteins can be
efficiently identified in distantly related organisms by sequence alignment. Genome and gene
sequences can be searched by a variety of tools for certain properties. Sequence profiling tools can
find restriction enzyme sites, open reading frames in nucleotide sequences, and predict secondary
structures. Phylogenetic trees can be constructed and evolutionary hypotheses developed using
special software like ClustalW regarding the ancestry of modern organisms and the genes they
express. The field of bioinformatics is now indispensable for the analysis of genes and proteins.
Structure determination
Discovering the tertiary structure of a protein, or the quaternary structure of its complexes, can
provide important clues about how the protein performs its function and how it can be affected, i.e.
in drug design. As proteins are too small to be seen under a light microscope, other methods have to
be employed to determine their structure. Common experimental methods include X-ray
crystallography and NMR spectroscopy, both of which can produce structural information
at atomic resolution. However, NMR experiments are able to provide information from which a
subset of distances between pairs of atoms can be estimated, and the final possible conformations
for a protein are determined by solving a distance geometry problem. Dual polarisation
interferometry is a quantitative analytical method for measuring the overall protein
conformation and conformational changes due to interactions or other stimulus. Circular dichroism is
another laboratory technique for determining internal β-sheet / α-helical composition of
proteins. Cryoelectron microscopy is used to produce lower-resolution structural information about
very large protein complexes, including assembled viruses;[58] a variant known as electron
crystallography can also produce high-resolution information in some cases, especially for two-
dimensional crystals of membrane proteins.[59] Solved structures are usually deposited in the Protein
Data Bank (PDB), a freely available resource from which structural data about thousands of proteins
can be obtained in the form of Cartesian coordinates for each atom in the protein.[60]
Many more gene sequences are known than protein structures. Further, the set of solved structures
is biased toward proteins that can be easily subjected to the conditions required in X-ray
crystallography, one of the major structure determination methods. In particular, globular proteins
are comparatively easy to crystallize in preparation for X-ray crystallography. Membrane proteins
and large protein complexes, by contrast, are difficult to crystallize and are underrepresented in the
PDB.[61] Structural genomicsinitiatives have attempted to remedy these deficiencies by systematically
solving representative structures of major fold classes. Protein structure prediction methods attempt
to provide a means of generating a plausible structure for proteins whose structures have not been
experimentally determined.[62]
Structure prediction and simulation
Constituent amino-acids can be analyzed to predict secondary, tertiary and quaternary protein structure, in this
case hemoglobin containing heme units

Main articles: Protein structure prediction and List of protein structure prediction software
Complementary to the field of structural genomics, protein structure prediction develops
efficient mathematical models of proteins to computationally predict the molecular formations in
theory, instead of detecting structures with laboratory observation.[63] The most successful type of
structure prediction, known as homology modeling, relies on the existence of a "template" structure
with sequence similarity to the protein being modeled; structural genomics' goal is to provide
sufficient representation in solved structures to model most of those that remain.[64]Although
producing accurate models remains a challenge when only distantly related template structures are
available, it has been suggested that sequence alignment is the bottleneck in this process, as quite
accurate models can be produced if a "perfect" sequence alignment is known.[65] Many structure
prediction methods have served to inform the emerging field of protein engineering, in which novel
protein folds have already been designed.[66] A more complex computational problem is the
prediction of intermolecular interactions, such as in molecular docking and protein–protein
interaction prediction.[67]
Mathematical models to simulate dynamic processes of protein folding and binding involve molecular
mechanics, in particular, molecular dynamics. Monte Carlo techniques facilitate the computations,
which exploit advances in parallel and distributed computing (for example,
the Folding@home project[68] which performs molecular modeling on GPUs). In silico simulations
discovered the folding of small α-helical protein domains such as the villin headpiece[69] and
the HIV accessory protein.[70] Hybrid methods combining standard molecular dynamics with quantum
mechanical mathematics explored the electronic states of rhodopsins.[71]
Protein disorder and unstructure prediction
Many proteins (in Eucaryota ~33%) contain large unstructured but biologically functional segments
and can be classified as intrinsically disordered proteins.[72] Predicting and analysing protein disorder
is, therefore, an important part of protein structure characterisation.[73]

Nutrition
Further information: Protein (nutrient) and Protein quality
Most microorganisms and plants can biosynthesize all 20 standard amino acids, while animals
(including humans) must obtain some of the amino acids from the diet.[27] The amino acids that an
organism cannot synthesize on its own are referred to as essential amino acids. Key enzymes that
synthesize certain amino acids are not present in animals—such as aspartokinase, which catalyses
the first step in the synthesis of lysine, methionine, and threonine from aspartate. If amino acids are
present in the environment, microorganisms can conserve energy by taking up the amino acids from
their surroundings and downregulating their biosynthetic pathways.
In animals, amino acids are obtained through the consumption of foods containing protein. Ingested
proteins are then broken down into amino acids through digestion, which typically
involves denaturation of the protein through exposure to acid and hydrolysis by enzymes
called proteases. Some ingested amino acids are used for protein biosynthesis, while others are
converted to glucose through gluconeogenesis, or fed into the citric acid cycle. This use of protein as
a fuel is particularly important under starvation conditions as it allows the body's own proteins to be
used to support life, particularly those found in muscle.[74]
In animals such as dogs and cats, protein maintains the health and quality of the skin by promoting
hair follicle growth and keratinization, and thus reducing the likelihood of skin problems producing
malodours.[75] Poor-quality proteins also have a role regarding gastrointestinal health, increasing the
potential for flatulence and odorous compounds in dogs because when proteins reach the colon in
an undigested state, they are fermented producing hydrogen sulfide gas, indole, and skatole.[76] Dogs
and cats digest animal proteins better than those from plants but products of low-quality animal
origin are poorly digested, including skin, feathers, and connective tissue.[76]

History and etymology

Further information: History of molecular biology
Proteins were recognized as a distinct class of biological molecules in the eighteenth century
by Antoine Fourcroy and others, distinguished by the molecules' ability
to coagulate or flocculate under treatments with heat or acid.[77] Noted examples at the time included
albumin from egg whites, blood serum albumin, fibrin, and wheat gluten.
Proteins were first described by the Dutch chemist Gerardus Johannes Mulder and named by the
Swedish chemist Jöns Jacob Berzelius in 1838.[78][79] Mulder carried out elemental analysis of
common proteins and found that nearly all proteins had the same empirical formula,
C400H620N100O120P1S1.[80] He came to the erroneous conclusion that they might be composed of a single
type of (very large) molecule. The term "protein" to describe these molecules was proposed by
Mulder's associate Berzelius; protein is derived from the Greek word πρώτειος (proteios), meaning
"primary",[81] "in the lead", or "standing in front",[82] + -in. Mulder went on to identify the products of
protein degradation such as the amino acid leucine for which he found a (nearly correct) molecular
weight of 131 Da.[80] Prior to "protein", other names were used, like "albumins" or "albuminous
materials" (Eiweisskörper, in German).[83]
Early nutritional scientists such as the German Carl von Voit believed that protein was the most
important nutrient for maintaining the structure of the body, because it was generally believed that
"flesh makes flesh."[84] Karl Heinrich Ritthausen extended known protein forms with the identification
of glutamic acid. At the Connecticut Agricultural Experiment Station a detailed review of the
vegetable proteins was compiled by Thomas Burr Osborne. Working with Lafayette Mendel and
applying Liebig's law of the minimum in feeding laboratory rats, the nutritionally essential amino
acids were established. The work was continued and communicated by William Cumming Rose. The
understanding of proteins as polypeptides came through the work of Franz Hofmeister and Hermann
Emil Fischer in 1902.[85][86] The central role of proteins as enzymes in living organisms was not fully
appreciated until 1926, when James B. Sumner showed that the enzyme urease was in fact a
protein.[87]
The difficulty in purifying proteins in large quantities made them very difficult for early protein
biochemists to study. Hence, early studies focused on proteins that could be purified in large
quantities, e.g., those of blood, egg white, various toxins, and digestive/metabolic enzymes obtained
from slaughterhouses. In the 1950s, the Armour Hot Dog Co. purified 1 kg of pure bovine
pancreatic ribonuclease A and made it freely available to scientists; this gesture helped ribonuclease
A become a major target for biochemical study for the following decades.[80]

John Kendrew with model of myoglobin in progress

 Linus Pauling is credited with the successful prediction of regular protein secondary structures based
on hydrogen bonding, an idea first put forth by William Astbury in 1933.[88] Later work by Walter
Kauzmann on denaturation,[89][90] based partly on previous studies by Kaj Linderstrøm-
Lang,[91] contributed an understanding of protein folding and structure mediated by hydrophobic
interactions.
The first protein to be sequenced was insulin, by Frederick Sanger, in 1949. Sanger correctly
determined the amino acid sequence of insulin, thus conclusively demonstrating that proteins
consisted of linear polymers of amino acids rather than branched chains, colloids, or cyclols.[92] He
won the Nobel Prize for this achievement in 1958.[93]
The first protein structures to be solved were hemoglobin and myoglobin, by Max Perutz and Sir
John Cowdery Kendrew, respectively, in 1958.[94][95] As of 2017, the Protein Data Bank has over
126,060 atomic-resolution structures of proteins.[96] In more recent times, cryo-electron microscopy of
large macromolecular assemblies[97] and computational protein structure prediction of small
protein domains[98] are two methods approaching atomic resolution.

See also

 Biology portal

 Biotechnology portal
 Molecular and cellular biology portal

 Medicine portal

 Chemistry portal

 Food portal

 Sharks portal

 Ecology portal

 Environment portal

 Metabolism portal

 Dentistry portal

 Technology portal

 Science portal
 Oregon portal

 Evolutionary biology portal

 Animals portal

 Deproteination
 DNA-binding protein
 Macromolecule
 Intein
 List of proteins
 Proteopathy
 Proteopedia
 Proteolysis
 Protein sequence space
 Protein superfamily

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Textbooks
Protein
From Wikipedia, the free encyclopedia
Jump to navigationJump to search
This article is about a class of molecules. For protein as a nutrient, see protein (nutrient). For other
uses, see protein (disambiguation).

A representation of the 3D structure of the protein myoglobin showing turquoise α-helices. This protein was the
first to have its structure solved by X-ray crystallography. Towards the right-center among the coils, a prosthetic
group called a heme group(shown in gray) with a bound oxygen molecule (red).

Proteins are large biomolecules, or macromolecules, consisting of one or more long chains
of amino acid residues. Proteins perform a vast array of functions within organisms,
including catalysing metabolic reactions, DNA replication, responding to stimuli, providing structure
to cells and organisms, and transporting molecules from one location to another. Proteins differ from
one another primarily in their sequence of amino acids, which is dictated by the nucleotide
sequence of their genes, and which usually results in protein foldinginto a specific three-dimensional
structure that determines its activity.
A linear chain of amino acid residues is called a polypeptide. A protein contains at least one long
polypeptide. Short polypeptides, containing less than 20–30 residues, are rarely considered to be
proteins and are commonly called peptides, or sometimes oligopeptides. The individual amino acid
residues are bonded together by peptide bonds and adjacent amino acid residues. The sequence of
amino acid residues in a protein is defined by the sequence of a gene, which is encoded in
the genetic code. In general, the genetic code specifies 20 standard amino acids; however, in certain
organisms the genetic code can include selenocysteine and—in certain archaea—pyrrolysine.
Shortly after or even during synthesis, the residues in a protein are often chemically modified
by post-translational modification, which alters the physical and chemical properties, folding, stability,
activity, and ultimately, the function of the proteins. Sometimes proteins have non-peptide groups
attached, which can be called prosthetic groups or cofactors. Proteins can also work together to
achieve a particular function, and they often associate to form stable protein complexes.
Once formed, proteins only exist for a certain period and are then degraded and recycled by the
cell's machinery through the process of protein turnover. A protein's lifespan is measured in terms of
its half-life and covers a wide range. They can exist for minutes or years with an average lifespan of
1–2 days in mammalian cells. Abnormal or misfolded proteins are degraded more rapidly either due
to being targeted for destruction or due to being unstable.
Like other biological macromolecules such as polysaccharides and nucleic acids, proteins are
essential parts of organisms and participate in virtually every process within cells. Many proteins
 are enzymes that catalyse biochemical reactions and are vital to metabolism. Proteins also have
structural or mechanical functions, such as actin and myosin in muscle and the proteins in
the cytoskeleton, which form a system of scaffolding that maintains cell shape. Other proteins are
important in cell signaling, immune responses, cell adhesion, and the cell cycle. In animals, proteins
are needed in the diet to provide the essential amino acids that cannot
be synthesized. Digestion breaks the proteins down for use in the metabolism.
Proteins may be purified from other cellular components using a variety of techniques such
as ultracentrifugation, precipitation, electrophoresis, and chromatography; the advent of genetic
engineering has made possible a number of methods to facilitate purification. Methods commonly
used to study protein structure and function include immunohistochemistry, site-directed
mutagenesis, X-ray crystallography, nuclear magnetic resonance and mass spectrometry.

Contents

 1Biochemistry
o 1.1Interactions
o 1.2Abundance in cells
 2Synthesis
o 2.1Biosynthesis
o 2.2Chemical synthesis
 3Structure
o 3.1Protein domains
o 3.2Sequence motif
 4Cellular functions
o 4.1Enzymes
o 4.2Cell signaling and ligand binding
o 4.3Structural proteins
 5Methods of study
o 5.1Protein purification
o 5.2Cellular localization
o 5.3Proteomics
o 5.4Bioinformatics
o 5.5Structure determination
o 5.6Structure prediction and simulation
 5.6.1Protein disorder and unstructure prediction
 6Nutrition
 7History and etymology
 8See also
 9References
 10Textbooks
 11External links
o 11.1Databases and projects
o 11.2Tutorials and educational websites

Biochemistry
Chemical structure of the peptide bond (bottom) and the three-dimensional structure of a peptide bond between
an alanine and an adjacent amino acid (top/inset). The bond itself is made of the CHONelements.

Resonance structures of the peptide bond that links individual amino acids to form a protein polymer

Main articles: Biochemistry, Amino acid, and Peptide bond

Most proteins consist of linear polymers built from series of up to 20 different L-α- amino acids.
All proteinogenic amino acids possess common structural features, including an α-carbon to which
an amino group, a carboxyl group, and a variable side chain are bonded. Only proline differs from
this basic structure as it contains an unusual ring to the N-end amine group, which forces the CO–
NH amide moiety into a fixed conformation.[1] The side chains of the standard amino acids, detailed
in the list of standard amino acids, have a great variety of chemical structures and properties; it is
the combined effect of all of the amino acid side chains in a protein that ultimately determines its
three-dimensional structure and its chemical reactivity.[2] The amino acids in a polypeptide chain are
linked by peptide bonds. Once linked in the protein chain, an individual amino acid is called
a residue, and the linked series of carbon, nitrogen, and oxygen atoms are known as the main
chain or protein backbone.[3]
The peptide bond has two resonance forms that contribute some double-bond character and inhibit
rotation around its axis, so that the alpha carbons are roughly coplanar. The other two dihedral
angles in the peptide bond determine the local shape assumed by the protein backbone.[4] The end
with a free amino group is known as the N-terminus or amino terminus, whereas the end of the
protein with a free carboxyl group is known as the C-terminus or carboxy terminus (the sequence of
the protein is written from N-terminus to C-terminus, from left to right).
The words protein, polypeptide, and peptide are a little ambiguous and can overlap in
meaning. Protein is generally used to refer to the complete biological molecule in a
stable conformation, whereas peptide is generally reserved for a short amino acid oligomers often
lacking a stable three-dimensional structure. However, the boundary between the two is not well
defined and usually lies near 20–30 residues.[5] Polypeptide can refer to any single linear chain of
amino acids, usually regardless of length, but often implies an absence of a defined conformation.
Interactions
Proteins can interact with many types of molecules, including with other proteins, with lipids, with
carboyhydrates, and with DNA.[6][7][8][9]
Abundance in cells
It has been estimated that average-sized bacteria contain about 2 million proteins per cell (e.g. E.
coli and Staphylococcus aureus). Smaller bacteria, such as Mycoplasma or spirochetes contain
fewer molecules, on the order of 50,000 to 1 million. By contrast, eukaryotic cells are larger and thus
contain much more protein. For instance, yeast cells have been estimated to contain about 50
million proteins and human cells on the order of 1 to 3 billion.[10] The concentration of individual
protein copies ranges from a few molecules per cell up to 20 million.[11] Not all genes coding proteins
are expressed in most cells and their number depends on, for example, cell type and external
stimuli. For instance, of the 20,000 or so proteins encoded by the human genome, only 6,000 are
detected in lymphoblastoid cells.[12] Moreover, the number of proteins the genomeencodes correlates
well with the organism complexity. Eukaryotes have 15,000, bacteria have 3,200, archaea have
2,400, and viruses have 42 proteins on average coded in their respective genomes.[13]

Synthesis
Biosynthesis

A ribosome produces a protein using mRNA as template

The DNA sequence of a gene encodes the amino acid sequence of a protein

Main article: Protein biosynthesis

Proteins are assembled from amino acids using information encoded in genes. Each protein has its
own unique amino acid sequence that is specified by the nucleotide sequence of the gene encoding
this protein. The genetic code is a set of three-nucleotide sets called codons and each three-
nucleotide combination designates an amino acid, for example AUG (adenine-uracil-guanine) is the
code for methionine. Because DNA contains four nucleotides, the total number of possible codons is
64; hence, there is some redundancy in the genetic code, with some amino acids specified by more
than one codon.[14] Genes encoded in DNA are first transcribed into pre-messenger RNA (mRNA) by
proteins such as RNA polymerase. Most organisms then process the pre-mRNA (also known as
a primary transcript) using various forms of Post-transcriptional modification to form the mature
mRNA, which is then used as a template for protein synthesis by the ribosome. In prokaryotes the
mRNA may either be used as soon as it is produced, or be bound by a ribosome after having moved
away from the nucleoid. In contrast, eukaryotes make mRNA in the cell nucleus and
then translocate it across the nuclear membrane into the cytoplasm, where protein synthesis then
takes place. The rate of protein synthesis is higher in prokaryotes than eukaryotes and can reach up
to 20 amino acids per second.[15]
The process of synthesizing a protein from an mRNA template is known as translation. The mRNA is
loaded onto the ribosome and is read three nucleotides at a time by matching each codon to its base
pairing anticodon located on a transfer RNA molecule, which carries the amino acid corresponding
to the codon it recognizes. The enzyme aminoacyl tRNA synthetase "charges" the tRNA molecules
with the correct amino acids. The growing polypeptide is often termed the nascent chain. Proteins
are always biosynthesized from N-terminus to C-terminus.[14]
The size of a synthesized protein can be measured by the number of amino acids it contains and by
its total molecular mass, which is normally reported in units of daltons (synonymous with atomic
mass units), or the derivative unit kilodalton (kDa). The average size of a protein increases from
Archaea to Bacteria to Eukaryote (283, 311, 438 residues and 31, 34, 49 kDa respecitvely) due to a
bigger number of protein domains constituting proteins in higher organisms.[13] For
instance, yeast proteins are on average 466 amino acids long and 53 kDa in mass.[5] The largest
known proteins are the titins, a component of the muscle sarcomere, with a molecular mass of
almost 3,000 kDa and a total length of almost 27,000 amino acids.[16]
Chemical synthesis
Main article: Peptide synthesis
Short proteins can also be synthesized chemically by a family of methods known as peptide
synthesis, which rely on organic synthesis techniques such as chemical ligation to produce peptides
in high yield.[17] Chemical synthesis allows for the introduction of non-natural amino acids into
polypeptide chains, such as attachment of fluorescent probes to amino acid side chains.[18] These
methods are useful in laboratory biochemistry and cell biology, though generally not for commercial
applications. Chemical synthesis is inefficient for polypeptides longer than about 300 amino acids,
and the synthesized proteins may not readily assume their native tertiary structure. Most chemical
synthesis methods proceed from C-terminus to N-terminus, opposite the biological reaction.[19]

Structure

The crystal structure of the chaperonin, a huge protein complex. A single protein subunit is highlighted.
Chaperonins assist protein folding.

Three possible representations of the three-dimensional structure of the protein triose phosphate
isomerase. Left: All-atom representation colored by atom type. Middle: Simplified representation illustrating the
backbone conformation, colored by secondary structure. Right: Solvent-accessible surface representation
colored by residue type (acidic residues red, basic residues blue, polar residues green, nonpolar residues
white).

Main article: Protein structure

Further information: Protein structure prediction
Most proteins fold into unique 3-dimensional structures. The shape into which a protein naturally
folds is known as its native conformation.[20] Although many proteins can fold unassisted, simply
through the chemical properties of their amino acids, others require the aid of
molecular chaperones to fold into their native states.[21] Biochemists often refer to four distinct
aspects of a protein's structure:[22]

 Primary structure: the amino acid sequence. A protein is a polyamide.

 Secondary structure: regularly repeating local structures stabilized by hydrogen bonds. The
most common examples are the α-helix, β-sheet and turns. Because secondary structures are
local, many regions of different secondary structure can be present in the same protein
molecule.
 Tertiary structure: the overall shape of a single protein molecule; the spatial relationship of the
secondary structures to one another. Tertiary structure is generally stabilized by nonlocal
interactions, most commonly the formation of a hydrophobic core, but also through salt bridges,
hydrogen bonds, disulfide bonds, and even posttranslational modifications. The term "tertiary
structure" is often used as synonymous with the term fold. The tertiary structure is what controls
the basic function of the protein.
 Quaternary structure: the structure formed by several protein molecules (polypeptide chains),
usually called protein subunits in this context, which function as a single protein complex.
Proteins are not entirely rigid molecules. In addition to these levels of structure, proteins may shift
between several related structures while they perform their functions. In the context of these
functional rearrangements, these tertiary or quaternary structures are usually referred to as
"conformations", and transitions between them are called conformational changes. Such changes
are often induced by the binding of a substrate molecule to an enzyme's active site, or the physical
region of the protein that participates in chemical catalysis. In solution proteins also undergo
variation in structure through thermal vibration and the collision with other molecules.[23]

Molecular surface of several proteins showing their comparative sizes. From left to right are: immunoglobulin
G (IgG, an antibody), hemoglobin, insulin (a hormone), adenylate kinase (an enzyme), and glutamine
synthetase (an enzyme).

Proteins can be informally divided into three main classes, which correlate with typical tertiary
structures: globular proteins, fibrous proteins, and membrane proteins. Almost all globular proteins
are soluble and many are enzymes. Fibrous proteins are often structural, such as collagen, the
major component of connective tissue, or keratin, the protein component of hair and nails.
Membrane proteins often serve as receptors or provide channels for polar or charged molecules to
pass through the cell membrane.[24]
A special case of intramolecular hydrogen bonds within proteins, poorly shielded from water attack
and hence promoting their own dehydration, are called dehydrons.[25]
Protein domains
Main article: Protein domain
Many proteins are composed of several protein domains, i.e. segments of a protein that fold into
distinct structural units. Domains usually also have specific functions, such as enzymatic activities
(e.g. kinase) or they serve as binding modules (e.g. the SH3 domain binds to proline-rich sequences
in other proteins).
Sequence motif
Short amino acid sequences within proteins often act as recognition sites for other proteins.[26] For
instance, SH3 domains typically bind to short PxxP motifs (i.e. 2 prolines[P], separated by 2
unspecified amino acids [x], although the surrounding amino acids may determine the exact binding
specificity). A large number of such motifs has been collected in the Eukaryotic Linear Motif (ELM)
database.

Cellular functions
Proteins are the chief actors within the cell, said to be carrying out the duties specified by the
information encoded in genes.[5] With the exception of certain types of RNA, most other biological
molecules are relatively inert elements upon which proteins act. Proteins make up half the dry weight
of an Escherichia coli cell, whereas other macromolecules such as DNA and RNA make up only 3%
and 20%, respectively.[27] The set of proteins expressed in a particular cell or cell type is known as
its proteome.

The enzyme hexokinase is shown as a conventional ball-and-stick molecular model. To scale in the top right-
hand corner are two of its substrates, ATP and glucose.

The chief characteristic of proteins that also allows their diverse set of functions is their ability to bind
other molecules specifically and tightly. The region of the protein responsible for binding another
molecule is known as the binding site and is often a depression or "pocket" on the molecular surface.
This binding ability is mediated by the tertiary structure of the protein, which defines the binding site
pocket, and by the chemical properties of the surrounding amino acids' side chains. Protein binding
can be extraordinarily tight and specific; for example, the ribonuclease inhibitor protein binds to
human angiogenin with a sub-femtomolar dissociation constant(<10−15 M) but does not bind at all to
its amphibian homolog onconase (>1 M). Extremely minor chemical changes such as the addition of
a single methyl group to a binding partner can sometimes suffice to nearly eliminate binding; for
example, the aminoacyl tRNA synthetase specific to the amino acid valine discriminates against the
very similar side chain of the amino acid isoleucine.[28]
Proteins can bind to other proteins as well as to small-molecule substrates. When proteins bind
specifically to other copies of the same molecule, they can oligomerize to form fibrils; this process
occurs often in structural proteins that consist of globular monomers that self-associate to form rigid
fibers. Protein–protein interactions also regulate enzymatic activity, control progression through
the cell cycle, and allow the assembly of large protein complexes that carry out many closely related
reactions with a common biological function. Proteins can also bind to, or even be integrated into,
cell membranes. The ability of binding partners to induce conformational changes in proteins allows
the construction of enormously complex signaling networks.[29] As interactions between proteins are
reversible, and depend heavily on the availability of different groups of partner proteins to form
aggregates that are capable to carry out discrete sets of function, study of the interactions between
specific proteins is a key to understand important aspects of cellular function, and ultimately the
properties that distinguish particular cell types.[30][31]
Enzymes
Main article: Enzyme
The best-known role of proteins in the cell is as enzymes, which catalyse chemical reactions.
Enzymes are usually highly specific and accelerate only one or a few chemical reactions. Enzymes
carry out most of the reactions involved in metabolism, as well as manipulating DNA in processes
such as DNA replication, DNA repair, and transcription. Some enzymes act on other proteins to add
or remove chemical groups in a process known as posttranslational modification. About 4,000
reactions are known to be catalysed by enzymes.[32] The rate acceleration conferred by enzymatic
catalysis is often enormous—as much as 1017-fold increase in rate over the uncatalysed reaction in
the case of orotate decarboxylase (78 million years without the enzyme, 18 milliseconds with the
enzyme).[33]
The molecules bound and acted upon by enzymes are called substrates. Although enzymes can
consist of hundreds of amino acids, it is usually only a small fraction of the residues that come in
contact with the substrate, and an even smaller fraction—three to four residues on average—that
are directly involved in catalysis.[34] The region of the enzyme that binds the substrate and contains
the catalytic residues is known as the active site.
Dirigent proteins are members of a class of proteins that dictate the stereochemistry of a compound
synthesized by other enzymes.[35]
Cell signaling and ligand binding

Ribbon diagram of a mouse antibody against cholera that binds a carbohydrate antigen

Many proteins are involved in the process of cell signaling and signal transduction. Some proteins,
such as insulin, are extracellular proteins that transmit a signal from the cell in which they were
synthesized to other cells in distant tissues. Others are membrane proteins that act
as receptors whose main function is to bind a signaling molecule and induce a biochemical response
in the cell. Many receptors have a binding site exposed on the cell surface and an effector domain
within the cell, which may have enzymatic activity or may undergo a conformational change detected
by other proteins within the cell.[36]
Antibodies are protein components of an adaptive immune system whose main function is to
bind antigens, or foreign substances in the body, and target them for destruction. Antibodies can
be secreted into the extracellular environment or anchored in the membranes of specialized B
cells known as plasma cells. Whereas enzymes are limited in their binding affinity for their substrates
by the necessity of conducting their reaction, antibodies have no such constraints. An antibody's
binding affinity to its target is extraordinarily high.[37]
Many ligand transport proteins bind particular small biomolecules and transport them to other
locations in the body of a multicellular organism. These proteins must have a high binding affinity
when their ligand is present in high concentrations, but must also release the ligand when it is
present at low concentrations in the target tissues. The canonical example of a ligand-binding
protein is haemoglobin, which transports oxygenfrom the lungs to other organs and tissues in
all vertebrates and has close homologs in every biological kingdom.[38] Lectins are sugar-binding
proteins which are highly specific for their sugar moieties. Lectins typically play a role in
biological recognition phenomena involving cells and proteins.[39] Receptors and hormones are highly
specific binding proteins.
Transmembrane proteins can also serve as ligand transport proteins that alter the permeability of the
cell membrane to small molecules and ions. The membrane alone has a hydrophobic core through
which polar or charged molecules cannot diffuse. Membrane proteins contain internal channels that
allow such molecules to enter and exit the cell. Many ion channel proteins are specialized to select
for only a particular ion; for example, potassium and sodium channels often discriminate for only one
of the two ions.[40]
Structural proteins
Structural proteins confer stiffness and rigidity to otherwise-fluid biological components. Most
structural proteins are fibrous proteins; for example, collagen and elastin are critical components
of connective tissue such as cartilage, and keratin is found in hard or filamentous structures such
as hair, nails, feathers, hooves, and some animal shells.[41] Some globular proteins can also play
structural functions, for example, actin and tubulin are globular and soluble as monomers,
but polymerize to form long, stiff fibers that make up the cytoskeleton, which allows the cell to
maintain its shape and size.
Other proteins that serve structural functions are motor proteins such as myosin, kinesin,
and dynein, which are capable of generating mechanical forces. These proteins are crucial for
cellular motility of single celled organisms and the sperm of many multicellular organisms which
reproduce sexually. They also generate the forces exerted by contracting muscles[42] and play
essential roles in intracellular transport.

Methods of study
Main article: Protein methods
The activities and structures of proteins may be examined in vitro, in vivo, and in silico. In
vitro studies of purified proteins in controlled environments are useful for learning how a protein
carries out its function: for example, enzyme kinetics studies explore the chemical mechanism of an
enzyme's catalytic activity and its relative affinity for various possible substrate molecules. By
contrast, in vivo experiments can provide information about the physiological role of a protein in the
context of a cell or even a whole organism. In silico studies use computational methods to study
proteins.
Protein purification
Main article: Protein purification
To perform in vitro analysis, a protein must be purified away from other cellular components. This
process usually begins with cell lysis, in which a cell's membrane is disrupted and its internal
contents released into a solution known as a crude lysate. The resulting mixture can be purified
using ultracentrifugation, which fractionates the various cellular components into fractions containing
soluble proteins; membrane lipids and proteins; cellular organelles, and nucleic
acids. Precipitation by a method known as salting out can concentrate the proteins from this lysate.
Various types of chromatography are then used to isolate the protein or proteins of interest based on
properties such as molecular weight, net charge and binding affinity.[43] The level of purification can
be monitored using various types of gel electrophoresis if the desired protein's molecular weight
and isoelectric point are known, by spectroscopy if the protein has distinguishable spectroscopic
features, or by enzyme assays if the protein has enzymatic activity. Additionally, proteins can be
isolated according to their charge using electrofocusing.[44]
For natural proteins, a series of purification steps may be necessary to obtain protein sufficiently
pure for laboratory applications. To simplify this process, genetic engineeringis often used to add
chemical features to proteins that make them easier to purify without affecting their structure or
activity. Here, a "tag" consisting of a specific amino acid sequence, often a series
of histidine residues (a "His-tag"), is attached to one terminus of the protein. As a result, when the
lysate is passed over a chromatography column containing nickel, the histidine residues ligate the
nickel and attach to the column while the untagged components of the lysate pass unimpeded. A
number of different tags have been developed to help researchers purify specific proteins from
complex mixtures.[45]
Cellular localization

Proteins in different cellular compartments and structures tagged with green fluorescent protein(here, white)

The study of proteins in vivo is often concerned with the synthesis and localization of the protein
within the cell. Although many intracellular proteins are synthesized in the cytoplasm and
membrane-bound or secreted proteins in the endoplasmic reticulum, the specifics of how proteins
are targeted to specific organelles or cellular structures is often unclear. A useful technique for
assessing cellular localization uses genetic engineering to express in a cell a fusion
protein or chimera consisting of the natural protein of interest linked to a "reporter" such as green
fluorescent protein(GFP).[46] The fused protein's position within the cell can be cleanly and efficiently
visualized using microscopy,[47] as shown in the figure opposite.
Other methods for elucidating the cellular location of proteins requires the use of known
compartmental markers for regions such as the ER, the Golgi, lysosomes or vacuoles, mitochondria,
chloroplasts, plasma membrane, etc. With the use of fluorescently tagged versions of these markers
or of antibodies to known markers, it becomes much simpler to identify the localization of a protein of
interest. For example, indirect immunofluorescence will allow for fluorescence colocalization and
demonstration of location. Fluorescent dyes are used to label cellular compartments for a similar
purpose.[48]
Other possibilities exist, as well. For example, immunohistochemistry usually utilizes an antibody to
one or more proteins of interest that are conjugated to enzymes yielding either luminescent or
chromogenic signals that can be compared between samples, allowing for localization information.
Another applicable technique is cofractionation in sucrose (or other material) gradients
using isopycnic centrifugation.[49] While this technique does not prove colocalization of a
compartment of known density and the protein of interest, it does increase the likelihood, and is
more amenable to large-scale studies.
Finally, the gold-standard method of cellular localization is immunoelectron microscopy. This
technique also uses an antibody to the protein of interest, along with classical electron microscopy
techniques. The sample is prepared for normal electron microscopic examination, and then treated
with an antibody to the protein of interest that is conjugated to an extremely electro-dense material,
usually gold. This allows for the localization of both ultrastructural details as well as the protein of
interest.[50]
Through another genetic engineering application known as site-directed mutagenesis, researchers
can alter the protein sequence and hence its structure, cellular localization, and susceptibility to
regulation. This technique even allows the incorporation of unnatural amino acids into proteins, using
modified tRNAs,[51] and may allow the rational design of new proteins with novel properties.[52]
Proteomics
Main article: Proteomics
The total complement of proteins present at a time in a cell or cell type is known as its proteome,
and the study of such large-scale data sets defines the field of proteomics, named by analogy to the
related field of genomics. Key experimental techniques in proteomics include 2D
electrophoresis,[53] which allows the separation of a large number of proteins, mass
spectrometry,[54] which allows rapid high-throughput identification of proteins and sequencing of
peptides (most often after in-gel digestion), protein microarrays, which allow the detection of the
relative levels of a large number of proteins present in a cell, and two-hybrid screening, which allows
the systematic exploration of protein–protein interactions.[55] The total complement of biologically
possible such interactions is known as the interactome.[56] A systematic attempt to determine the
structures of proteins representing every possible fold is known as structural genomics.[57]
Bioinformatics
Main article: Bioinformatics
A vast array of computational methods have been developed to analyze the structure, function, and
evolution of proteins.
The development of such tools has been driven by the large amount of genomic and proteomic data
available for a variety of organisms, including the human genome. It is simply impossible to study all
proteins experimentally, hence only a few are subjected to laboratory experiments while
computational tools are used to extrapolate to similar proteins. Such homologous proteins can be
efficiently identified in distantly related organisms by sequence alignment. Genome and gene
sequences can be searched by a variety of tools for certain properties. Sequence profiling tools can
find restriction enzyme sites, open reading frames in nucleotide sequences, and predict secondary
structures. Phylogenetic trees can be constructed and evolutionary hypotheses developed using
special software like ClustalW regarding the ancestry of modern organisms and the genes they
express. The field of bioinformatics is now indispensable for the analysis of genes and proteins.
Structure determination
Discovering the tertiary structure of a protein, or the quaternary structure of its complexes, can
provide important clues about how the protein performs its function and how it can be affected, i.e.
in drug design. As proteins are too small to be seen under a light microscope, other methods have to
be employed to determine their structure. Common experimental methods include X-ray
crystallography and NMR spectroscopy, both of which can produce structural information
at atomic resolution. However, NMR experiments are able to provide information from which a
subset of distances between pairs of atoms can be estimated, and the final possible conformations
for a protein are determined by solving a distance geometry problem. Dual polarisation
interferometry is a quantitative analytical method for measuring the overall protein
conformation and conformational changes due to interactions or other stimulus. Circular dichroism is
another laboratory technique for determining internal β-sheet / α-helical composition of
proteins. Cryoelectron microscopy is used to produce lower-resolution structural information about
very large protein complexes, including assembled viruses;[58] a variant known as electron
crystallography can also produce high-resolution information in some cases, especially for two-
dimensional crystals of membrane proteins.[59] Solved structures are usually deposited in the Protein
Data Bank (PDB), a freely available resource from which structural data about thousands of proteins
can be obtained in the form of Cartesian coordinates for each atom in the protein.[60]
Many more gene sequences are known than protein structures. Further, the set of solved structures
is biased toward proteins that can be easily subjected to the conditions required in X-ray
crystallography, one of the major structure determination methods. In particular, globular proteins
are comparatively easy to crystallize in preparation for X-ray crystallography. Membrane proteins
and large protein complexes, by contrast, are difficult to crystallize and are underrepresented in the
PDB.[61] Structural genomicsinitiatives have attempted to remedy these deficiencies by systematically
solving representative structures of major fold classes. Protein structure prediction methods attempt
to provide a means of generating a plausible structure for proteins whose structures have not been
experimentally determined.[62]
Structure prediction and simulation
Constituent amino-acids can be analyzed to predict secondary, tertiary and quaternary protein structure, in this
case hemoglobin containing heme units

Main articles: Protein structure prediction and List of protein structure prediction software
Complementary to the field of structural genomics, protein structure prediction develops
efficient mathematical models of proteins to computationally predict the molecular formations in
theory, instead of detecting structures with laboratory observation.[63] The most successful type of
structure prediction, known as homology modeling, relies on the existence of a "template" structure
with sequence similarity to the protein being modeled; structural genomics' goal is to provide
sufficient representation in solved structures to model most of those that remain.[64]Although
producing accurate models remains a challenge when only distantly related template structures are
available, it has been suggested that sequence alignment is the bottleneck in this process, as quite
accurate models can be produced if a "perfect" sequence alignment is known.[65] Many structure
prediction methods have served to inform the emerging field of protein engineering, in which novel
protein folds have already been designed.[66] A more complex computational problem is the
prediction of intermolecular interactions, such as in molecular docking and protein–protein
interaction prediction.[67]
Mathematical models to simulate dynamic processes of protein folding and binding involve molecular
mechanics, in particular, molecular dynamics. Monte Carlo techniques facilitate the computations,
which exploit advances in parallel and distributed computing (for example,
the Folding@home project[68] which performs molecular modeling on GPUs). In silico simulations
discovered the folding of small α-helical protein domains such as the villin headpiece[69] and
the HIV accessory protein.[70] Hybrid methods combining standard molecular dynamics with quantum
mechanical mathematics explored the electronic states of rhodopsins.[71]
Protein disorder and unstructure prediction
Many proteins (in Eucaryota ~33%) contain large unstructured but biologically functional segments
and can be classified as intrinsically disordered proteins.[72] Predicting and analysing protein disorder
is, therefore, an important part of protein structure characterisation.[73]

Nutrition
Further information: Protein (nutrient) and Protein quality
Most microorganisms and plants can biosynthesize all 20 standard amino acids, while animals
(including humans) must obtain some of the amino acids from the diet.[27] The amino acids that an
organism cannot synthesize on its own are referred to as essential amino acids. Key enzymes that
synthesize certain amino acids are not present in animals—such as aspartokinase, which catalyses
the first step in the synthesis of lysine, methionine, and threonine from aspartate. If amino acids are
present in the environment, microorganisms can conserve energy by taking up the amino acids from
their surroundings and downregulating their biosynthetic pathways.
In animals, amino acids are obtained through the consumption of foods containing protein. Ingested
proteins are then broken down into amino acids through digestion, which typically
involves denaturation of the protein through exposure to acid and hydrolysis by enzymes
called proteases. Some ingested amino acids are used for protein biosynthesis, while others are
converted to glucose through gluconeogenesis, or fed into the citric acid cycle. This use of protein as
a fuel is particularly important under starvation conditions as it allows the body's own proteins to be
used to support life, particularly those found in muscle.[74]
In animals such as dogs and cats, protein maintains the health and quality of the skin by promoting
hair follicle growth and keratinization, and thus reducing the likelihood of skin problems producing
malodours.[75] Poor-quality proteins also have a role regarding gastrointestinal health, increasing the
potential for flatulence and odorous compounds in dogs because when proteins reach the colon in
an undigested state, they are fermented producing hydrogen sulfide gas, indole, and skatole.[76] Dogs
and cats digest animal proteins better than those from plants but products of low-quality animal
origin are poorly digested, including skin, feathers, and connective tissue.[76]

History and etymology

Further information: History of molecular biology
Proteins were recognized as a distinct class of biological molecules in the eighteenth century
by Antoine Fourcroy and others, distinguished by the molecules' ability
to coagulate or flocculate under treatments with heat or acid.[77] Noted examples at the time included
albumin from egg whites, blood serum albumin, fibrin, and wheat gluten.
Proteins were first described by the Dutch chemist Gerardus Johannes Mulder and named by the
Swedish chemist Jöns Jacob Berzelius in 1838.[78][79] Mulder carried out elemental analysis of
common proteins and found that nearly all proteins had the same empirical formula,
C400H620N100O120P1S1.[80] He came to the erroneous conclusion that they might be composed of a single
type of (very large) molecule. The term "protein" to describe these molecules was proposed by
Mulder's associate Berzelius; protein is derived from the Greek word πρώτειος (proteios), meaning
"primary",[81] "in the lead", or "standing in front",[82] + -in. Mulder went on to identify the products of
protein degradation such as the amino acid leucine for which he found a (nearly correct) molecular
weight of 131 Da.[80] Prior to "protein", other names were used, like "albumins" or "albuminous
materials" (Eiweisskörper, in German).[83]
Early nutritional scientists such as the German Carl von Voit believed that protein was the most
important nutrient for maintaining the structure of the body, because it was generally believed that
"flesh makes flesh."[84] Karl Heinrich Ritthausen extended known protein forms with the identification
of glutamic acid. At the Connecticut Agricultural Experiment Station a detailed review of the
vegetable proteins was compiled by Thomas Burr Osborne. Working with Lafayette Mendel and
applying Liebig's law of the minimum in feeding laboratory rats, the nutritionally essential amino
acids were established. The work was continued and communicated by William Cumming Rose. The
understanding of proteins as polypeptides came through the work of Franz Hofmeister and Hermann
Emil Fischer in 1902.[85][86] The central role of proteins as enzymes in living organisms was not fully
appreciated until 1926, when James B. Sumner showed that the enzyme urease was in fact a
protein.[87]
The difficulty in purifying proteins in large quantities made them very difficult for early protein
biochemists to study. Hence, early studies focused on proteins that could be purified in large
quantities, e.g., those of blood, egg white, various toxins, and digestive/metabolic enzymes obtained
from slaughterhouses. In the 1950s, the Armour Hot Dog Co. purified 1 kg of pure bovine
pancreatic ribonuclease A and made it freely available to scientists; this gesture helped ribonuclease
A become a major target for biochemical study for the following decades.[80]

John Kendrew with model of myoglobin in progress

 Linus Pauling is credited with the successful prediction of regular protein secondary structures based
on hydrogen bonding, an idea first put forth by William Astbury in 1933.[88] Later work by Walter
Kauzmann on denaturation,[89][90] based partly on previous studies by Kaj Linderstrøm-
Lang,[91] contributed an understanding of protein folding and structure mediated by hydrophobic
interactions.
The first protein to be sequenced was insulin, by Frederick Sanger, in 1949. Sanger correctly
determined the amino acid sequence of insulin, thus conclusively demonstrating that proteins
consisted of linear polymers of amino acids rather than branched chains, colloids, or cyclols.[92] He
won the Nobel Prize for this achievement in 1958.[93]
The first protein structures to be solved were hemoglobin and myoglobin, by Max Perutz and Sir
John Cowdery Kendrew, respectively, in 1958.[94][95] As of 2017, the Protein Data Bank has over
126,060 atomic-resolution structures of proteins.[96] In more recent times, cryo-electron microscopy of
large macromolecular assemblies[97] and computational protein structure prediction of small
protein domains[98] are two methods approaching atomic resolution.

See also

 Biology portal

 Biotechnology portal
 Molecular and cellular biology portal

 Medicine portal

 Chemistry portal

 Food portal

 Sharks portal

 Ecology portal

 Environment portal

 Metabolism portal

 Dentistry portal

 Technology portal

 Science portal
 Oregon portal

 Evolutionary biology portal

 Animals portal

 Deproteination
 DNA-binding protein
 Macromolecule
 Intein
 List of proteins
 Proteopathy
 Proteopedia
 Proteolysis
 Protein sequence space
 Protein superfamily

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Textbooks
What Is Sports Nutrition?
Sports nutrition is the foundation of athletic success. It is a well-designed nutrition plan that
allows active adults and athletes to perform at their best. It supplies the right food type, energy,
nutrients, and fluids to keep the body well hydrated and functioning at peak levels. A sports
nutrition diet may vary day to day, depending on specific energy demands.

Sports nutrition is unique to each person and is planned according to individual goals.

Sports Nutrition Basics: Macronutrients

The energy required for living and physical activity comes from the food we eat and fluid intake.
Macronutrients in the following food groups supply the energy essential to optimal body
function:

 Carbohydrates are either simple or complex, and the most important energy source for
the human body. Simple carbs include sugars naturally occurring in foods like fruits,
vegetables, and milk. Whole grain bread, potatoes, most vegetables, and oats are
examples of healthy complex carbs. Your digestive system breaks
down carbohydrates into glucose or blood sugar which feeds energy to your cells, tissues,
and organs.
 Proteins are made up of a chain of amino acids and are essential to every cell of the
human body. Protein can either be complete or incomplete. A complete protein contains
all the amino acids needed by the body, and include animal sources like meat, fish,
poultry, and milk. Incomplete protein sources (typically plant-based proteins) often lack
one or more of the essential amino acids. Essential amino acids can't be made by the body
and must be supplied by food. Protein plays an important role in muscle recovery and
growth.
 Fats can be saturated or unsaturated, and they play a vital role in the human body.
Unsaturated fats are considered healthy and come from plant sources like olive oil and
nuts. Saturated fats are found in animal products like red meats and high-fat dairy, which
are indicated to increase the risk of disease. Healthy fats provide energy, help with body
development, protect our organs, and maintain cell membranes.

The Goal of Sports Nutrition

Active adults and competitive athletes turn to sports nutrition to help them achieve their goals.
Examples of individual goals could include gaining lean mass, improving body composition, or
enhancing athletic performance. These sport-specific scenarios require differing nutritional
programs. Research findings indicate the right food type, caloric intake, nutrient timing, fluids,
and supplementation are essential and specific to each individual. The following are different
states of training and competitive sport benefiting from sports nutrition:

Eating for Exercise/Athletic Performance

Training programs require a well-designed diet for active adults and competitive athletes.
Research shows a balanced nutrition plan should include sufficient calories and healthy
macronutrients to optimize athletic performance. The body will use carbohydrates or fats as the
main energy source, depending on exercise intensity and duration. Inadequate caloric intake can
impede athletic training and performance.

Active adults exercising three to four times weekly can usually meet nutritional needs through a
normal healthy diet. Moderate to elite athletes performing intense training five to six times
weekly will require significantly more nutrients to support energy demands.

For example, and according to research, energy expenditure for extreme cyclists competing in
the Tour de France is approximately 12,000 calories per day.

 Carbohydrates are the main fuel source for an active adult or competitive athlete.
General guidelines for carbohydrate intake are based on body size and training
characteristics. Carbohydrate needs in a daily diet can range from 45 to 65 percent of
total food intake depending on physical demands.
 Proteins are responsible for muscle growth and recovery in the active adult or
athlete. Sufficient amounts of protein per individual help maintain a positive nitrogen
balance in the body, which is vital to muscle tissue. Protein requirements can vary
significantly ranging from .8g to 2g per kilogram of body weight per day.
 Fats help maintain energy balance, regulate hormones, and restore muscle tissue. Omega-
3 and omega-6 are essential fatty acids that are especially important to a sports nutrition
diet. Research findings recommend an athlete consume approximately 30 percent of their
total daily caloric intake as a healthy fat.

Eating for Endurance

Endurance programs are defined as one to three hours per day of moderate to high-intensity
exercise. High-energy intake in the form of carbohydrates is essential. According to research,
target carbohydrate consumption for endurance athletes ranges from 6g to 10g per kilogram of
body weight per day. Fat is a secondary source of energy used during long-duration training
sessions. Endurance athletes are more at risk for dehydration. Replacing fluids and electrolytes
lost through sweat are necessary for peak performance.

Marathon Training and Race Day Diet and Fluids

Eating for Strength

Resistance training programs are designed to gradually build the strength of skeletal muscle.
Strength training is high-intensity work. It requires sufficient amounts of all macronutrients
for muscle development. Protein intake is especially vital to increase and maintain lean body
mass. Research indicates protein requirements can vary from 1.2g to 3.1g per kilogram of body
weight per day.
How to Eat to Gain Muscle

Eating for Competition

Preparing for a competitive sport will vary in sports nutrition requirements. For example,
strength athletes strive to increase lean mass and body size for their sport. Endurance runners
focus on reduced body weight/fat for peak body function during their event. Athletic goals will
determine the best sports nutrition strategy. Pre and post-workout meal planning are unique for
each athlete and essential for optimal performance.

Hydration and Sports Performance

Adequate hydration and electrolytes are essential for health and athletic performance. We all lose
water throughout the day, but active adults and athletes lose additional body water (and a
significant amount of sodium) sweating during intense workouts.

Dehydration is the process of losing body water, and fluid deficits greater than 2 percent of body
weight can compromise athletic performance and cognitive function. Athletes are recommended
to use fluid replacement strategies as part of their sports nutrition to maintain optimal body
functioning. Rehydration with water and sports drinks containing sodiumare often consumed
depending on the athlete and sporting event. Lack of sufficient hydration for athletes may lead to
the following:

 Hypohydration (dehydration)
 Hypovolemia (decreased plasma/blood volume)
 Hyponatremia (low blood sodium levels/water intoxication)

Supplements in Sports Nutrition

Sports supplements and foods are unregulated products marketed to enhance athletic
performance. According to the Academy of Sports Medicine, “the ethical use of sports
supplements is a personal choice and remains controversial.” There are limited
supplements backed by clinical research. The Australian Institute of Sport has provided a general
guide ranking sports performance supplements and foods according to the significance of
scientific evidence:

 Sports food: sports drinks, bars, and gels, electrolyte supplements, protein supplements,
liquid meal supplements
 Medical supplements: iron, calcium, vitamin D, multi-vitamin/mineral, omega-3 fatty
acids
 Performance supplements: creatine, caffeine, sodium bicarbonate, beta-alanine, nitrate

Sports Nutrition for Special Populations and Environments

Sports nutrition covers a wide spectrum of needs for athletes. Certain populations and
environments require additional guidelines and information to enhance athletic performance.

 Vegetarian athlete: A vegetarian diet contains high intakes of plant proteins, fruits,
vegetables, whole grains, and nuts. It can be nutritionally adequate, but insufficient
evidence exists on long-term vegetarianism and athletic performance. Dietary
assessments are recommended to avoid deficiencies and to ensure adequate nutrients to
support athletic demands.
 High altitude: Specialized training and nutrition are required for athletes training at high
altitude. Increasing red blood cells to carry more oxygen is essential. Iron-rich foods are
an important component for this athlete as well. Increased risk of illness is indicated with
chronic high altitude exposure. Foods high in antioxidants and protein are essential. Fluid
requirements will vary per athlete, and hydration status should be individually monitored.
 Hot environments: Athletes competing in hot conditions are at greater risk of heat
illness. Heat illness can have adverse health complications. Fluid and electrolyte balance
is crucial for these athletes. Hydration strategies are required to maintain peak
performance while exercising in the heat.

 Cold environments: Primary concerns for athletes exercising in the coldare adequate
hydration and body temperature. Leaner athletes are at higher risk of hypothermia.
Modifying caloric and carbohydrate intake are important for this athlete. Appropriate
foods and fluids that withstand cold temperatures will promote optimal athletic
performance.

Special Topics in Sports Nutrition

Eating disorders in athletes are not uncommon. Many athletes are required to maintain lean
bodies and low body weight and exhibit muscular development. Chronic competitive pressure
can create psychological and physical stress of the athlete leading to disordered eating habits.
Without proper counseling, adverse health effects may eventually develop. The most
common eating disorders among athletes may include:

 Anorexia nervosa
 Bulimia
 Compulsive exercise disorder
 Orthorexia

Obviously, the nutritional needs of these individuals greatly differ from that of other active
adults or athletes. Until someone with an eating disorder is considered well again, the primary
focus should be put on treating and managing the eating disorder and consuming the nutrition
needed to achieve and maintain good health, rather than athletic performance.

Micronutrient deficiencies are a concern for active adults and athletes. Exercise stresses
important body functions where micronutrients are required. Additionally, athletes often restrict
calories and certain food groups, which may potentially lead to deficiencies of essential
micronutrients. Research indicates the most common micronutrient deficiencies include:
  Iron deficiency: can impair muscle function and compromise athletic performance
 Vitamin D deficiency: can result in decreased bone strength and reduced muscle
metabolic function
 Calcium deficiency: can impair the repair of bone tissue, decrease regulation of muscle
contraction, and reduce nerve conduction

Roles of a Sports Dietitian

Athletes and active adults are seeking guidance from sports professionals to enhance their
athletic performance. Sports dietitians are increasingly hired to develop nutrition and fluid
programs catered to the individual athlete or teams. A unique credential has been created for
sports nutrition professionals: Board Certified Specialist in Sports Dietetics (CSSD). Sports
dietitians should have knowledge in the following areas:

 Clinical nutrition
 Nutrition science
 Exercise physiology
 Evidence-based research
 Safe and effective nutrition assessments
 Sports nutrition guidance
 Counseling for health and athletic performance
 Medical nutrition therapy
 Design and management of effective nutrition strategies
 Effective nutrition programming for health, fitness, and optimal physical performance
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STAYING HEALTHY
Sports Nutrition
Athletes who want a winning edge need the right nutrition. When you give your body the
right fuel by drinking enough water and eating a balanced diet, you will make the most
of your athletic talents and gain more strength, power, and endurance when you train.

This article contains some general sports nutrition guidelines. To achieve top
performance, your diet should be based on a variety of factors including your age,
weight, physical condition, and the type of exercise you are doing. Consult your doctor
for individualized sports nutrition advice.

Hydration
Water is the most important nutrient for athletes. Water comprises about 60% of body
weight and is essential for almost every bodily function. Because your body cannot make
or store water, you must replace the water that you lose in your urine and sweat.
Stay hydrated by drinking plenty of fluids before, during, and after exercise.
© Thinkstock, 2014

Everyone should drink at least two quarts (64 oz.) of water each day—and athletes need
even more. To stay hydrated and avoid overheating, drink plenty of fluids before,
during, and after sports or exercise. When you work out or compete, especially in hot
weather, try to replace the amount of water you lose in sweat by drinking the same
amount of fluid.

Drinking cool water is the best way to keep hydrated during workouts or events that last
an hour or less. Sports drinks made up of 6% to 10% carbohydrates can help you stay
hydrated during longer events. Most sports drinks should be diluted with approximately
50% water.

Because thirst is not a reliable way to tell if you need water, be sure to drink even if you
are not thirsty. You will not start feeling thirsty until you have already lost about 2% of
your body weight—enough to hurt performance. Also, if you stop drinking water as soon
as your thirst is satisfied, you will get only about half the amount you really need.

The following tips will help you stay hydrated:

 Drink small amounts of water frequently rather than large amounts less
often.
 Drink cool beverages to lower your core body temperature and reduce
sweating.
 Track your sweat loss by weighing yourself both before and after exercise.
For every pound lost through sweat, drink 16 to 24 oz. of water. Your body
weight should be back to normal before your next workout.
 Pay attention to the amount and color of your urine. A large volume of clear
urine is a sign that you are well-hydrated. Smaller amounts of urine, or dark
or concentrated-appearing yellow urine can indicate dehydration. If your
urine turns brown, it may be a sign of a more serious problem and you
should get medical attention immediately.
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Fuel Sources
A balanced diet is another key to sports nutrition. Eating the right combination of fuel
(calories) from carbohydrates, proteins, and fats will give you energy for top
performance.

Carbohydrates

Carbohydrates—the most important source of fuel—should provide about 60% to 70% of

your daily calories. Carbohydrates are found in many foods, including:
 Fruits
 Vegetables
 Pasta
 Bread
 Cereal
 Rice
Your body converts the sugars and starches in carbohydrates into energy (glucose) or
stores it in your liver and muscle tissues (glycogen). This gives you endurance and
power for high-intensity, short-duration activities.

If your body runs out of carbohydrate fuel during exercise it will burn fat and protein for
energy—causing your performance level to drop. This may happen if you start exercising
without enough stored muscle glycogen or if you exercise intensely for longer than an
hour without eating more carbohydrates. It may also happen if you do multiple
repetitions of high-intensity, short-duration exercises or if you participate in multiple
events or training sessions in a single day.
Eating fruit, or another food high in carbohydrates, will help you maintain energy during
competition.
© Thinkstock, 2014

The following tips will help you maintain carbohydrate fuel so that you can stay
energized and perform at your best:
 Start your exercise or competition with glycogen-loaded muscles by eating
carbohydrates for at least several days before the event.
 To replenish energy and delay fatigue, eat additional carbohydrates when
you exercise or compete for longer than one hour.

Proteins

Proteins should provide about 12% to 15% of your daily calories. Proteins are found in
many foods, including:
 Meat
 Fish
 Poultry
 Eggs
 Beans
 Nuts
 Dairy products
Good sources of protein include meat, cheese, eggs, and nuts
© Thinkstock, 2014

Proteins give your body the power to build new tissues and fluids among other
functions. Your body cannot store extra protein so it burns it for energy or converts it to
fat. The amount of protein you need depends, in part, on your:
 Level of fitness. Physically active people need more protein than those who
do not exercise. You also need more protein when you start an exercise
program.
 Exercise type, intensity, and duration. Endurance athletes often burn
protein for fuel, as do bodybuilders and other athletes who perform intense
strength-building activities.
 Total daily calories. Your body burns more protein if you do not consume
enough calories to maintain your body weight. This can happen if you eat
too little or exercise too much.
 Carbohydrate intake. Your body may use protein for energy if you exercise
with low levels of muscle glycogen or if you do repeated training sessions
without eating more carbohydrates. When you start with enough muscle
glycogen, protein supplies about 5% of your energy; otherwise, it may
supply up to 10%.

Fats

Fats should provide no more than 20% to 30% of your daily calories. Saturated fats
come from animal-based foods, such as meats, eggs, milk, and cheese. Unsaturated fats
are found in vegetable products such as corn oil.

Your body needs small amounts of fat for certain critical functions and as an alternative
energy source to glucose. Eating too much fat, however, is associated with heart disease,
some cancers, and other major health problems. Also, if you are eating too much fat, it
probably means that you are not eating enough carbohydrates.

How your body uses fat for energy depends on the intensity and duration of exercise.
For example, when you rest or exercise at low to moderate intensity, fat is the primary
fuel source. As you increase the intensity of your exercise your body uses more
carbohydrates for fuel. If your body uses up its glycogen supply and you continue
exercising you will burn fat for energy, decreasing the intensity of your exercise.

Nutrition before Competition

What you eat several days before an endurance activity affects performance. The food
you eat on the morning of a sports competition can ward off hunger, keep blood sugar
levels adequate, and aid hydration. Try to avoid eating high-protein or high-fat foods on
the day of an event.

To perform at your highest level, follow these general nutrition guidelines before an
event:
  Eat a meal high in carbohydrates.
 Eat solid foods 3 to 4 hours before an event. Drink liquids 2 to 3 hours
before an event.
 Choose easily digestible foods, rather than fried or high-fat foods.
 Avoid sugary foods and drinks within one hour of the event.
 Drink enough fluids to ensure hydration. A good guideline to follow is:
Drink 20 oz. of water 1 to 2 hours before exercise and an additional 10 to 15
oz. within 15 to 30 minutes of the event. Replenishing fluids lost to sweat is
the primary concern during an athletic event. Drink 3 to 6 ounces of water
or diluted sports drink every 10 to 20 minutes throughout competition.

Carbohydrate Loading

To avoid running out of carbohydrates for energy, some endurance athletes—including

long-distance runners, swimmers, and bicyclists—load their muscles with glycogen. To
do this, they eat extra carbohydrates and exercise to energy depletion several days
before an event. To "carbohydrate load" before an event:
 First, exercise to muscle fatigue. Your workout must be identical to the
upcoming event to deplete the right muscles.
 Next, eat a high-carbohydrate diet (70% to 80% carbohydrates, 10% to 15%
protein, and 10% to15% fat), and do little or no exercise for three days
before the event.
Some endurance athletes believe that following this carbohydrate-loading regimen will
ensure that muscles loaded with unused glycogen will be available to work for longer
periods of time during competition. You should always consult with your doctor for
advice before trying a carbohydrate-loading diet.
Most people need between 1,500 and 2,000 calories a day. For athletes, this number can
increase by 500 to 1,000 more calories. Talk to your doctor about your or your child's nutrition
needs. They can help you determine a healthy daily caloriecount

As an athlete, your physical health is key to an active lifestyle. You depend on

strength, skill, and endurance, whether you’re going for the ball or making that
final push across the finish line. Being your best takes time, training, and
patience, but that’s not all. Like a car, your body won’t run without the right
fuel. You must take special care to get enough of the calories, vitamins, and
other nutrients that provide energy.

Path to well being

Every person’s needs are different. The amount of food you need depends on
your age, height, weight, and sport or activity level. In general, you need to
replace the number of calories you burn each day. Calories measure the
energy you get from food. Most people need between 1,500 and 2,000
calories a day. For athletes, this number can increase by 500 to 1,000 more
calories.

Talk to your doctor about your or your child’s nutrition needs. They can help
you determine a healthy daily calorie count. Over time, you will learn how to
balance your intake and outtake to avoid extreme weight gain or loss.

Calories come in different forms. The main types are carbohydrates, fats, and
proteins.

 Carbohydrates (carbs) are your body’s biggest source of calories.

Simple carbs are easier for your body to break down. They provide quick
bursts of energy. Complex carbs take longer for your body to break down.
 They are a better source of energy over time. Complex carbs in whole
grain products are the most nutritious. Examples include: whole-grain
bread, potatoes, brown rice, oatmeal, and kidney beans. Doctors
recommend that 55% to 60% of your daily calories come from
carbohydrates.

 Fat is another important source of calories. In small amounts, fat is a key

fuel source. It serves other functions, such as supporting good skin and
hair. Do not replace carbs in your diet with fats. This can slow you down,
because your body has to work harder to burn fat for energy. Fats should
make up no more than 30% of your daily calories. When you can, choose
unsaturated fats, like olive oil and nuts. These are better for your health
than saturated and trans fats. Too much fat or the wrong kinds can cause
health problems. It can raise your bad (LDL) cholesterol level and increase
your risk of heart disease and type 2 diabetes.

 Protein should make up the remaining 10% to 15% of your daily calories.
Protein is found in foods like meat, eggs, milk, beans, and nuts. Some
athletes think they should consume large amounts of protein. While
protein does help build muscle, high doses won’t help you bulk up. Over
time, too much protein can be harmful to your health. The digestion
process can put strain on your liver and kidneys.

Athletes need the same vitamins and minerals as everyone else. There are
no guidelines for additional nutrients or supplements. To stay healthy, eat a
balanced, nutrient-rich diet. It should include foods full of calcium, iron,
potassium, and fiber. You also need key vitamins, such as A, C, and E. Try
not to be tempted by junk foods, which are an empty source of calories.
Instead, focus on lean meats, whole grains, and a mixture of fruits and
vegetables to fuel your body.

Know when to eat and rehydrate

For athletes, knowing when to eat is as important as knowing what to eat. Try
to eat a pre-game meal 2 to 4 hours before your event. For a race, this could
be dinner the night before. A good pre-game meal is high in complex carbs
and low in protein and sugar. Avoid rich and greasy foods. These can be
harder for you to digest and can cause an upset stomach. You may find it
helpful to avoid food the hour before a sporting event. This is because
digestion uses up energy.

Staying hydrated is the most important thing athletes can do. This is
especially true on game day. Your body is made up of nearly 60% water.
During a workout, you quickly lose fluid when you sweat. Thirst is a sign of
dehydration. Don’t wait until you are thirsty to drink. A good rule of thumb is to
take a drink at least every 15 to 20 minutes. But, don’t drink so much that you
feel full.

Water is the best way to rehydrate. For short events (under an hour), water
can replace what you lose from sweating. For longer events, you may benefit
from sports drinks. They provide electrolytes and carbohydrates. Many
experts now recommend drinking chocolate milk after exercise. The protein in
milk helps with muscle recovery. It can have less sugar than sports or energy
drinks, and contains many vitamins and minerals. Avoid drinks that contain
caffeine. They can dehydrate you more and cause you to feel anxious or
jittery.
Things to consider
Athletes require a lot of energy and nutrients to stay in shape. Because of this,
strict diet plans can hurt your ability and be harmful to your health. Without the
calories from by carbs, fat, and protein, you may not have enough strength.
Not eating enough also can lead to malnutrition. Female athletes can have
abnormal menstrual cycles. You increase your risk of osteoporosis, a fragile
bone condition caused in part from a lack of calcium. Get medical help if you
and your coach think you need to lose weight. Be sure to talk to your doctor
before making major nutrition changes.

Questions to ask your doctor

 How many calories does my child need to eat each day?
 Are there any supplements they should take?
The Academy of Nutrition and Dietetics, Dietitians of Canada and the American College
of Sports Medicine recommend 1.2 to 2.0 grams of protein per kilogram of body weight per
day for athletes, depending on training. Protein intake should be spaced throughout the day
and after workouts.
The recommended dietary allowance for the average, sedentary or lightly active adult is 0.8
grams per kilogram of body weight per day. For most people, this is more than enough.
However, protein needs for athletes may range from 1.2 to 1.7 grams per kilogram of body
weight per day.
Eating for Peak Athletic Performance

Every athlete strives for an edge over the competition. Daily training and recovery require a comprehensive
eating plan that matches these physical demands. The keys to peak nutrition performance aimed to
complement your training and competition are reviewed below.

Food Energy

The energy needs of athletes exceed those of the average person. It’s not uncommon for male and female
athletes, especially those still growing, to have caloric needs exceeding 2,400-3,000 kcal and 2,200-2,700
kcal per day, respectively. The amount of energy found within a given food is dependent on the
macronutrient (carbohydrate, protein and fat) content of the item.

Macro-nutrient Energy Content

Carbohydrates 4 kcal/gram

Protein 4 kcal/gram

Alcohol* 7 kcal/gram

Fat 9 kcal/gram

*Although alcohol is not considered a macronutrient, it’s important for athletes to realize that it is higher in
calories and can contribute to undesirable weight gain.

 Carbohydrates serve as the primary source of energy during activities of higher intensity. Healthy
carbohydrate food sources include fruits, vegetables, whole-grain cereals, breads and pastas.
 Dietary fat also plays a key role in helping individuals meet their energy needs as well as supporting
healthy hormone levels. Healthy sources of fat include nuts, nut butters, avocados, olive and
coconut oils. Limit use of vegetable oils such as corn, cottonseed or soybean oil.
 Dietary protein plays a key role in muscle repair and growth. Preferred sources of protein include
lean meats, eggs, dairy (yogurt, milk, cottage cheese) and legumes.

UW Health Sports Performance

The sports performance coaches, physical therapists and athletic trainers in the UW Health Sports
Performance program develop comprehensive programs accessible to athletes of all ages and ability levels,
with an emphasis on long-term athlete development.

View our program

Tips to Excel with Proper Sports Nutrition

1. Make a plan to eat a variety of fruits and vegetables daily. The goal is to eat at least five servings
per day, and include varieties of fruit and vegetable color. One serving is approximately the size of
a baseball. Fruits and vegetables are filled with the energy and nutrients necessary for training and
recovery. Plus, these antioxidant-rich foods will help you combat illness like a cold or the flu.
2. Choose whole grain carbohydrates sources such as whole-wheat bread or pasta, and fiber-rich
cereals as power-packed energy sources. Limit the refined grains and sugars such as sugary
cereals, white breads and bagels. You'll benefit more from whole-grain products.
3. Choose healthy sources of protein such as chicken, turkey, fish, peanut butter, eggs, nuts and
legumes.
4. Stay hydrated with beverages, as a two percent drop in hydration levels can negatively impact
performance. Options include milk, water, 100 percent fruit juice and sport drinks. However, realize
that sport drinks and 100 percent fruit juice tend to be higher in overall sugar content and, in the
case of fruit juice, lack many of the health benefits present in its whole food counterpart. Also, be
sure not to confuse sports drinks such as Gatorade with "energy" drinks such as Red Bull and
similar beverages.
5. Stick with whole food options as much as possible as opposed to highly processed foods.

Planning a Nutritious Meal

Without adequate calories from the healthiest food sources, you will struggle to achieve your performance
goals. Plan a nutritious meal by choosing at least one food from each category.

Carbohydrates Protein Healthy Fat

Fruit Whole eggs ( white and yolk) Avocado
Oatmeal Greek yogurt Peanut butter
Starchy vegetables Milk Nuts and seeds
(sweet/white potatoes, squash)
Non-starchy vegetables String cheese Olive or canola oil (the latter,
(broccoli, leafy greens) if baking)
Whole-grain bread or crackers Lean red meats Coconut oil
High-fiber, non-sugary cereals Poultry Flax seed (add to baking or
cooking)
Quinoa Fish
Brown or wild rice Hummus

Hydration

Adequate hydration is a key element in sports performance. Most athletes benefit from developing a
personal hydration plan. A general rule for training is to consume a minimum:

 Two cups of fluid prior to training

 Four to six ounces of fluid every 15 minutes of exercise

Your post event/training hydration needs are impacted by your overall pre- to post-fluid losses. To properly
assess, weigh yourself immediately prior to and after a workout. For every pound of weight lost, replace
with 16 ounces of fluid. Best hydration choices include water, low-fat milk or 100 percent juice. Sports
beverages are best reserved for competition, where quick hydration and electrolyte replacement are
necessary.

Game Day Nutrition

There are a few golden rules when it comes to eating on game day:

 Remember, proper nutrition for the "big tournament/race/meet" does not happen on the day of the
event alone. It happens the days, weeks, and months leading up to the competition
 Never experiment with a new dietary/supplement protocol on game day. First, try it out prior to a
practice/training session to make sure you tolerate it well.
 As you get closer to the game/competition, make your meals smaller. Additionally, you may want to
limit dairy, fat and fibrous carbohydrate sources during the last one to one and one-half hours pre-
event/practice, as these may cause GI issues.

On-the-go Eating

Peak performance during competition means eating nutritious food while traveling. Relying on the
concession stand for food during competition is an almost certain failure. Players (and parents) should
prepare by packing a variety of food and beverages.

Choose energy-packed foods such as whole grain crackers with low-fat cheese, tortilla wraps with veggies
and lean meat, hard-boiled eggs, vegetable or bean soups, small boxes of non-sugary cereal, fresh fruit,
mini-whole wheat bagels with peanut butter, pita bread with hummus or pasta with grilled chicken. Pair any
of these options with fruit/vegetable and milk and you’ve got a great meal.
Healthy Food Choices Not-so-healthy Food Choices
Grilled chicken, turkey or fish Fried chicken and fish
Lean beef or pork Burgers, sausage, bacon
Fruits, vegetables, salads, French fries, fried rice, alfredo or cheese sauce
veggie-based soups
Nuts, trail mix, seeds or peanut Chips, cheese curls, pork rinds
butter
Eggs or egg substitutes Omelets loaded with cheese, hash browns and
sausage
Whole grain breads, rice and Highly-processed white bread, rice and pasta
pasta
Dairy products Dairy products with excessive added sugars, like
ice cream

 As you get closer to the game/competition, make your meals smaller, removing fats and dairy
products. Fibrous carbohydrates can be beneficial as these tend to cause GI disturbances.
 The key thing with “pre-event” nutrition is making sure that you’ve tested it out before game day.
Try the pre-meal/snack protocol in advance to make sure you tolerate it well.
Food as Fuel Before, During and After
Workouts

Your body is your vehicle, so you have to keep your engine running when you work out.
That means fueling up your body by eating the right foods and drinking the right fluids,
in the right amounts at the right times.
The American College of Sports Medicine says, “Adequate food and fluid should be
consumed before, during, and after exercise to help maintain blood glucose
concentration during exercise, maximize exercise performance, and improve recovery
time. Athletes should be well hydrated before exercise and drink enough fluid during
and after exercise to balance fluid losses.”

“You don’t have to adhere to a rigid schedule and there are no hard-fast rules,” said
Riska Platt, M.S., R.D., a nutrition consultant for the Cardiac Rehabilitation Center at
Mount Sinai Medical Center in New York. “But there are some things you should do
before, during and after you work out.”

Here is what Ms. Platt recommends:

Before: Fuel Up!

Not fueling up before you work out is like “driving a car on empty,” said Platt, an
American Heart Association volunteer. You also won’t have enough energy to maximize
your workout and you limit your ability to burn calories.

Ideally, fuel up two hours before you exercise by:

 Hydrating with water.

 Eating healthy carbohydrates such as whole-grain cereals (with low-fat or skim milk),
whole-wheat toast, low-fat or fat-free yogurt, whole grain pasta, brown rice, fruits and
vegetables.
 Avoiding saturated fats and even a lot of healthy protein — because these types of fuels
digest slower in your stomach and take away oxygen and energy-delivering blood from
your muscles.

If you only have 5-10 minutes before you exercise, eat a piece of fruit such as an apple
or banana.

“The key is to consume easily digested carbohydrates, so you don’t feel sluggish,” Platt
said.

During: Make a Pit Stop.

Whether you’re a professional athlete who trains for several hours or you have a low to
moderate routine, keep your body hydrated with small, frequent sips of water.

Platt notes that you don’t need to eat during a workout that’s an hour or less. But, for
longer, high-intensity vigorous workouts, she recommends eating 50-100 calories every
half hour of carbohydrates such as low-fat yogurt, raisins, or banana.

After: Refuel Your Tank.

After your workout, Ms. Platt recommends refueling with:

 Fluids. Drink water, of course. Blend your water with 100% juice such as orange juice
which provides fluids, carbohydrates.

 Carbohydrates. You burn a lot of carbohydrates — the main fuel for your muscles —
when you exercise. In the 20-60 minutes after your workout, your muscles can store
carbohydrates and protein as energy and help in recovery.

 Protein. Eat things with protein to help repair and grow your muscles.

It’s important to realize that these are general guidelines. We have different digestive
systems and “a lot depends on what kind of workout you’re doing,” Platt said.

So do what works best for you. Know that what you put in your body (nutrition) is as
important as you what you do with you

Your body is your vehicle, so you have to keep your engine — your heart — running when you work out.

That means fueling up your tank with the right foods and your radiator with the right fluids, using with right amounts at
the right times. The American College of Sports Medicine says, “Adequate food and fluid should be consumed before,
during, and after exercise to help maintain blood glucose concentration during exercise, maximize exercise
performance, and improve recovery time. Athletes should be well hydrated before exercise and drink enough fluid
during and after exercise to balance fluid losses.”

“You don’t have to adhere to a rigid schedule and there are no hard-fast rules,” said Riska Platt, M.S., R.D., a
nutrition consultant for the Cardiac Rehabilitation Center at Mount Sinai Medical Center in New York. “But there are
some things you should do before, during and after you work out.”

Here is what Ms. Platt recommends:

Before: Fuel Up!

Not fueling up before you work out is like “driving a car on empty,” said Platt, an American Heart Association
volunteer. You also won’t have enough energy to maximize your workout and you limit your ability to burn calories.

Ideally, fuel up two hours before you exercise by:

 Hydrating with water.

 Eating healthy carbohydrates such as whole-grain cereals (with low-fat or skim milk), whole-wheat toast
(without the fatty cream cheese), low-fat or fat-free yogurt, whole grain pasta, brown rice, fruits and
vegetables.
 Avoiding saturated fats and even a lot of healthy protein — because these types of fuels digest slower in
your stomach and take away oxygen and energy-delivering blood from your muscles.

If you only have 5-10 minutes before you exercise, eat a piece of fruit such as an apple or banana.

“The key is to consume easily digested carbohydrates, so you don’t feel sluggish,” Platt said.

During: Make a Pit Stop

Whether you’re a professional athlete who trains for several hours or you have a low to moderate routine, keep your
body hydrated with small, frequent sips of water.

Platt notes that you don’t need to eat during a workout that’s an hour or less. But, for longer, high intensity vigorous
workouts, she recommends eating 50-100 calories every half hour of carbohydrates such as raisins, an energy bar or
banana.

After: Refuel Your Tank

After your workout, Ms. Platt recommends refueling with:

 Fluids. Drink water, of course. Blend your water with 100% juice such as orange juice which provides fluids,
carbohydrates.

 Carbohydrates. You burn a lot of carbohydrates — the main fuel for your muscles — when you exercise. In
the 20-60 minutes after your workout, your muscles can store carbohydrates and protein as energy and help
in recovery.

 Protein. Eat things with protein to help repair and grow your muscles. It’s important to realize that these are
general guidelines. We have different digestive systems and “a lot depends on what kind of workout you’re
doing,” Platt said.

So do what works best for you. Know that what you put in your body (nutrition) is as important as you what
you do with your body (exercise). Both are crucial to keeping your engine performing at its best.

Learn more:

 Learn the American Heart Association's Recommendations for Physical Activity in Adults
 5 Steps to Loving Exercise ... Or At Least Not Hating It
 Getting Physically Active After a Cardiac Event