Gen.

Bio
Biomolecules

Biological Molecule Monomer Polymer Chemical Bond

Carbohydrate Monosaccharides Polysaccharides Glycosidic Bond

Lipid Fatty Acids and Ester

Glycerol

Nucleic Acid Nucleotides Polynucleotides Hydrogen Bond

Phosphodiester Bond

Protein Amino Acid Polypeptide Peptide Bond

Carbohydrates

• Carbohydrates are also known as “Saccharides”, from “Sakcharon” meaning sugar.

• “Optically active polyhydroxy aldehydes or polyhydroxy ketones or substances which give
these on hydrolysis are termed as carbohydrates”.
• The body breaks them down into glucose, which provides energy.
o Carbohydrates are mainly found in plant foods. They also occur in dairy products
in the form of a milk sugar called lactose. Foods high in carbohydrates include
bread, pasta, beans, potatoes, rice, and cereals.
• Carbohydrates play several roles in living organisms, including providing energy. By
products of carbohydrates are involved in the immune system, the development of
disease, blood clotting, and reproduction.
• Consists of 2 carbonyl group, being:
o Aldose (aldehyde group) – the group connected to the last carbon, having a
carbon single bonded with hydrogen and double bonded to an oxygen.
o Ketose (ketone group) – the group connected near the last carbon, double
bonded to an oxygen atom.
Classification of Carbohydrates

The main classification of carbohydrate is done on the basis of hydrolysis. This classification is
as follow:

• Monosaccharides (C6H12O6): These are the simplest form of carbohydrate that cannot
be hydrolyzed any further. Some common examples are glucose, Ribose etc.
o Glucose (Blood Sugar): The most common form of sugar in plants. Glucose is
the type of sugar that our bodies use for fuel. No matter what forms of sugar we
eat, our bodies break most of them down into glucose. Glucose pairs with other
simple sugars to form the disaccharides.
o Galactose (Brain Sugar): These made up of the same elements as glucose, but
they are arranged differently. Galactose is mainly found as a monosaccharide in
peas.
o Fructose (Fruit Sugar): A type of sugar that is found in fruits, honey, and some
root vegetables. Fructose is the sweetest of all naturally occurring sugars. Fructose
can only be metabolized in your liver.
• Disaccharides (C12H22O11): The term disaccharide etymologically means two
saccharides. A saccharide refers to the unit structure of carbohydrates. Thus, a
disaccharide is a carbohydrate comprised of two saccharides (or two monosaccharide
units).
o Maltose (Malt Sugar): These are made of two glucose molecules bound together.
It naturally occurs as the byproduct of breaking down carbohydrates. It's found in
sprouted grains. Grains produce it when they break down starch to sprout.
▪ 1 carbon of glucose is bonded to the 4 carbon of glucose, a 1-4
glycosidic linkage. (not bonded to 4 carbon numerically, 4 in position)
o Lactose (Milk Sugar): The sugar naturally found in milk and dairy products.
Lactose is made up of glucose and galactose. Lactose produces lactic acid, which
is needed for fermentation to make yogurt and cheese. You need a specific
enzyme known as lactase to break down lactose into glucose and galactose so
that your body can absorb it. If you don't have that enzyme, you may be lactose-
intolerant.
▪ 1 carbon of glucose is bonded to the 4 carbon of galactose, a 1-4
glycosidic linkage. (not bonded to 4 carbon numerically, 4 in position)
o Sucrose (Table Sugar): These are made of one part glucose and one part
fructose joined together. Sucrose is naturally found in plants. Table sugar is
sucrose. It's usually made from sugarcane or sugar beets.
▪ 1 carbon of glucose is bonded to the 2 carbon of fructose, a 1-2
glycosidic linkage. (not bonded to 2 carbon numerically, 2 in position)

• Polysaccharides [(C6H10O5)n]: The final category of carbohydrates. These give a

large number of monosaccharides when they undergo hydrolysis, these carbohydrates
are not sweet in taste and are also known as non-sugars. Some common examples are
starch, glycogen etc.
o Starch (Plant Starch):
 o Glycogen (Animal Starch):
o Cellulose (Plant Fiber or Dietary Fiber):

Lipids

• Lipids are organic compounds that contain hydrogen, carbon, and oxygen atoms which
form the framework for the structure and function of living cells.
• These are biological molecules that tend to be nonpolar and are made up mostly of
hydrocarbon chains. Lipids store energy, provide insulation, make up cell membranes,
and provide building blocks for hormones.
• Composed of carbon, hydrogen, and oxygen with no definite ratio, the number of oxygen
atoms is very much less compared to hydrogen atoms.
• A lipid molecule is composed of 1 glycerol and 3 fatty acids through the process of
dehydration synthesis. Storage of energy and important component of the cell membrane.

• In foods, lipids are mainly found in the form of triacylglycerols (triacylglycerides) (TAG),
which make up to 99% of lipids of plant and animal origin.
 • These organic compounds are nonpolar molecules, which are soluble only in nonpolar
solvents and insoluble in water because water is a polar molecule. In the human body,
these molecules can be synthesized in the liver and are found in oil, butter, whole milk,
cheese, fried foods and also in some red meats.
• Lipids are fatty, waxy, or oily compounds that are essential to many body functions and
serve as the building blocks for all living cells. Lipids help regulate hormones, transmit
nerve impulses, cushion organs, and store energy in the form of body fat.

Properties of Lipids

Lipids are a family of organic compounds, composed of fats and oils. These molecules yield high
energy and are responsible for different functions within the human body. Listed below are some
important characteristics of Lipids.

1. Lipids are oily or greasy nonpolar molecules, stored in the adipose tissue of the body.

2. Lipids are a heterogeneous group of compounds, mainly composed of hydrocarbon

chains.

3. Lipids are energy-rich organic molecules, which provide energy for different life processes.

4. Lipids are a class of compounds characterized by their solubility in nonpolar solvents and
insolubility in water.

5. Lipids are significant in biological systems as they form a mechanical barrier dividing a
cell from the external environment known as the cell membrane.
Fatty Acids

Fatty acids are a defining feature of lipids. A fatty acid is a long hydrocarbon (alkyl) chain with an
acidic head. The acidic head is more correctly known as a ‘carboxylic acid’ and has the chemical
structure -COOH, the same structure that makes vinegar acidic.
A fatty acid can be saturated or unsaturated. If two carbon atoms of the hydrocarbon chain share
a double bond then a fatty acid is known as ‘unsaturated’.

Fats and Oil

A fat molecule consists of two kinds of parts: a glycerol backbone and three fatty acid tails.
Glycerol is a small organic molecule with three hydroxyl (OH) groups, while a fatty acid consists
of a long hydrocarbon chain attached to a carboxyl group. A typical fatty acid contains 12–18
carbons, though some may have as few as 4 or as many as 36.

To make a fat molecule, the hydroxyl groups on the glycerol backbone react with the carboxyl
groups of fatty acids in a dehydration synthesis reaction. This yields a fat molecule with three fatty
acid tails bound to the glycerol backbone via ester linkages (linkages containing an oxygen atom
next to a carbonyl, or C=O, group). Triglycerides may contain three identical fatty acid tails, or
three different fatty acid tails (with different lengths or patterns of double bonds).

Fat molecules are also called triacylglycerols, or, in bloodwork done by your
doctor, triglycerides. In the human body, triglycerides are primarily stored in specialized fat cells,
called adipocytes, which make up a tissue known as adipose tissue. While many fatty acids are
found in fat molecules, some are also free in the body, and they are considered a type of lipid in
their own right.

Phospholipids
Phospholipids are less well-known than fats and oils but are essential to life on Earth. They are
the molecules used to build the membranes found around and inside cells. Without a plasma
membrane, a cell would not be able to survive.

A phospholipid is similar in structure to a triacylglycerol. It contains TWO fatty acids plus a

phosphate group bonded to the three carbons of a glycerol molecule. The sole difference between
a phospholipid and a fat is the replacement of one fatty acid with a phosphate group.

Phospholipids (PL) are important structural lipids in foods and cell membranes. Most of
the PL are removed by degumming in the refining of vegetable and fish oils and these oils
therefore mainly consist of triacylglycerols, but in foods such as egg, meat and
fish, phospholipids can constitute a larger part of the lipids (e.g. cod phospholipids constitute 87%
of the total lipids).

Phosphatidylcholine (PC),

• a major constituent of cell membranes and pulmonary surfactant, and is more commonly
found in the exoplasmic or outer leaflet of a cell membrane.
• it is thought to be transported between membranes within the cell by phosphatidylcholine
transfer protein (PCTP).

Phosphatidylethanolamine (PE),

• are found particularly in nervous tissue such as the white matter of brain, nerves, neural
tissue, and in spinal cord
• play a role in membrane fusion and in disassembly of the contractile ring during cytokinesis
in cell division
• it is thought that phosphatidylethanolamine regulates membrane curvature.

Phosphatidylglycerol (PG),

• are crucial components of biological membranes. These membranes are found in cells
and organelles, and they serve as barriers that separate the interior of these structures
from the external environment.

Phosphatidylinositol (PI),

• this modulates the function of membrane proteins.

• helps in lipid signaling, cell signaling and membrane trafficking.

Phosphatidylserine (PS).

• a phospholipid that protects the cells in your brain.

• transmits messages in your brain to help your memory and cognitive function.
Steroids

• Steroids are a particular type of lipid with a unique chemical structure. They are
characterized by having carbon atoms arranged into four adjacent rings three rings made
from 6 carbon atoms and the final ring made from 5 carbon atoms. Steroids are produced
naturally in the body. Examples include cholesterol and the sex hormones testosterone,
progesterone and estrogen. Cholesterol is the most abundant steroid in the body and is
produced in the brain, blood and nerve tissue.
• Steroid hormones are divided into mineralocorticoids, glucocorticoids, androgens,
estrogens, and progestogens.
• They can also be made in a lab and used as treatments for certain health conditions, such
as arthritis, asthma, and some skin conditions. These drugs are known as corticosteroids,
or steroids for short.
• Cholesterol is a type of steroid in the sense that it belongs to the sterols, a subgroup of
steroids due to their similar chemical structure. However, cholesterol is also the main
precursor in steroid synthesis. This means that all naturally occurring steroid hormones
are derived from cholesterol.

10 Natural Steroids

• Spinach
• Banana
• Asparagus
• Figs
 • Eggs
• Oysters
• Quinoa
• Avocado
• Fava beans
• Wild oats

What role does cholesterol play in the body?

The right amount of cholesterol helps the body function properly. It’s a major building block for cell
membranes and plays a key role in metabolism and digestion.

While too much cholesterol can pose health risks, the right amount has numerous benefits.
Here are some of the functions of cholesterol in the body:

• Helps in making certain hormones that facilitate the body’s normal functioning, like sex
hormones and cortisol

• Plays a key role in digestion as the liver uses it to make bile acids, which help break down
fats

• Helps build the body’s cells

• Helps in vitamin D synthesis

• Facilitates normal functioning of the cell membranes

Cholesterol is a precursor to vitamins and hormones like vitamin D, estrogen, and cortisol. It is
also one of the main components of the cell membrane. Approximately 65–80% of the cellular
cholesterol in your body is found in the cells’ plasma membranes.

• HDL (Good Cholesterol): This helps remove bad cholesterol from the body.
• LDL (Bad Cholesterol): This can cause plaque that clog arteries.
Nucleic Acid (omfg I hate the slides in SB)

Are large biomolecules that play essential roles in all cells and viruses. A major function of nucleic acids
involves the storage and expression of genomic information. Deoxyribonucleic acid, or DNA, encodes the
information cells need to make proteins.

Nucleoside = nitrogenous base + sugar

Nucleotide = nucleoside + phosphate group

Gene

• A segment of DNA that codes for a protein, which in turn codes for a trait (skin tone, eye
color, etc.)

• A gene is a stretch of DNA.

Deoxyribonucleic Acid

• It is a nucleic acid that contains the genetic information for the development and function
of organism.

Structure of DNA

DNA is made up of a series of monomers called nucleotides. DNA is a twisted-ladder called a

DOUBLE HELIX DNA Nucleotide.
DNA Nucleotide structure:

1. Phosphate group
2. 5–carbon sugar: Deoxyribose/Ribose
3. Nitrogenous base

Nitrogenous Bases

There are two families of nitrogenous bases;

• Pyrimidines (cytosine, thymine, and uracil) have a single six-membered ring

• Purines (adenine and guanine) have a six-membered ring fused to a five-membered ring

Erwin Chargaff discovered the base pairing rules and ratios for different species. Wilkins has
become a historical footnote and Watson & Crick are remembered as the Fathers of DNA.

Chargaff’s (Base Pairing) Rule

• Adenine (A) must always pair with Thymine (T) due to their 2 hydrogen bonds.
• Cytosine (C) must always pair with Guanine (G) due to their 3 hydrogen bonds.
o Hydrogen bonds is used for the nitrogenous bases.

3 differences OF RNA from DNA

1. Single strand instead of double strand

2. Ribose instead of deoxyribose

3. Uracil instead of thymine

3 Types of RNA

RNA is used to obtain information from the DNA and synthesize protein.

• Messenger RNA (mRNA)

o Brings information from the DNA in the nucleus to the protein manufacturing
area, the CYTOPLASM.
• Transfer RNA (tRNA)
o Supplies amino acids to the ribosome to be assembled as protein.
o Anticodon-a sequence of 3 bases that are complementary base pairs to a codon
in the mRNA
• Ribosomal RNA (rRNA)
o is the structural component of ribosomes. It directs the translation of mRNA into
proteins.

Amino Acids

• These are the building blocks of protein.

• At least one kind of tRNA is present for each of the 20 amino acids used in protein
synthesis.

• Are created using codons, a 3 base pairs that code for a single amino acid

CENTRAL DOGMA OF MOLECULAR BIOLOGY

The central dogma of molecular biology is a theory stating that genetic information flows only in
one direction, from DNA, to RNA, to protein, or RNA directly to protein. This explains how DNA
codes for RNA, which codes for proteins.

Process of Central Dogma of Molecular Biology

DNA REPLICATION

DNA replication occurs before the cell divides so that each cell has a complete copy of DNA.
This is the process of making two identical copies of DNA from the original DNA molecule. The
process is semi-conservative, meaning that you conserve part of the original structure in the
new one.

• The 2 strands of DNA are complementary. (fit together like puzzle pieces)

• Each strand can serve as a pattern, to put together the sequence of bases on the other
half.
DNA TRANSCRIPTION

DNA transcription is the process by which the information in a strand of DNA is copied into a
new molecule of messenger RNA (mRNA).

Transcription is the first step in gene expression. It involves copying a gene's DNA sequence to
make an RNA molecule. Transcription is performed by enzymes called RNA polymerases, which
link nucleotides to form an RNA strand (using a DNA strand as a template).

DNA TRANSLATION

DNA translation is the process of translating the base sequence of an mRNA molecule to a
sequence of amino acid during protein synthesis.

• Initiation
o For translation to begin, the start codon (5’AUG) must be recognised. This codon
is specific to the amino acid methionine, which is nearly always the first amino
acid in a polypeptide chain.
o At the 5’ cap of mRNA, the small 40s subunit of the ribosome binds.
Subsequently, the larger 60s subunit binds to complete the initiation complex.
The next step (elongation) can now commence.
• Elongation
o The ribosome has two tRNA binding sites; the P site which holds the peptide
chain and the A site which accepts the tRNA.
o While Methionine-tRNA occupies the P site, the aminoacyl-tRNA that is
complementary to the next codon binds to the A site, using energy yielded from
the hydrolysis of GTP.
o Methionine moves from the P site to the A site to bond to a new amino acid there,
starting the growth of the peptide. The tRNA molecule in the P site no longer has
an attached amino acid, so leaves the ribosome.
o The ribosome then translocates along the mRNA molecule to the next codon,
again using energy yielded from the hydrolysis of GTP. Now, the growing peptide
lies at the P site and the A site is open for the binding of the next aminoacyl-
tRNA, and the cycle continues.
o The polypeptide chain is built up in the direction from the N terminal (methionine)
to the C terminal (the final amino acid).
• Termination
o One of the three stop codons enters the A site. No tRNA molecules bind to these
codons, so the peptide and tRNA in the P site become hydrolysed, therefore
releasing the polypeptide into the cytoplasm. The small and large subunits of the
ribosome then dissociate, ready for the next round of translation.

Protein
 • Proteins are large biomolecules made of one or multiple long chains of amino acids.
Amino acids are the building blocks of proteins.
o Amino acids are molecules that contain amine (-NH2) and carboxyl (-COOH)
groups. There are 22 kinds of amino acids known to be associated with living
things. For now, I won’t require you to memorize all 22 of them, but in college,
you will be required to. The thing that makes amino acids different from one
another is the side chain (R group). So, an amino acid is composed of an amino
group, a carboxyl group, and a side chain.

• The “R” symbol means “radical” which originated from Latin “radix” which means “root”.
Here are some representative amino acids. Notice the amino group, the carboxyl group,
and the R group.
• Amino acids bond with each other to form long chains. The type of chemical bond that
they have are called peptide bonds, hence the name of its polymer (polypeptide). A
polypeptide chain is unbranched and is approximately made up of 50 amino acids.
• These chains would form spirals, the loops would bond with other loops, and polypeptide
chains would bond with other polypeptide chains to form that whole complex protein
molecule.

Four Types of Protein Structure

1. Primary Structure

• The Primary structure of proteins is the exact ordering of amino acids forming
their chains.
• The exact sequence of the proteins is very important as it determines the final
fold and therefore the function of the protein.
• The number of polypeptide chains together form proteins. These chains have
amino acids arranged in a particular sequence which is characteristic of the
specific protein. Any change in the sequence changes the entire protein.

2. Secondary Structure
• Secondary structure of proteins refers to local folded structures formed by
interactions between atoms of the polypeptide backbone.
• Polypeptide chains fold due to interactions between amine and carboxyl groups
of peptide bonds.
• The structure results from regular folding due to hydrogen bonding between the -
CO and -NH groups.
• These local folds include spirals (alpha helices), extended shapes (beta sheets),
or loops.
• These folds are known as secondary elements and define the protein's
secondary structure.

o (a) α – Helix:
▪ α – Helix is one of the most common ways in which a polypeptide
chain forms all possible hydrogen bonds by twisting into a right-
handed screw with the -NH group of each amino acid residue
hydrogen-bonded to the -CO of the adjacent turn of the helix. The
polypeptide chains twisted into a right-handed screw.
o (b) β – pleated sheet:
▪ In this arrangement, the polypeptide chains are stretched out
beside one another and then bonded by intermolecular H-bonds.
In this structure, all peptide chains are stretched out to nearly
maximum extension and then laid side by side which is held
together by intermolecular hydrogen bonds. The structure
resembles the pleated folds of drapery and therefore is known as
β – pleated sheet.
 3. Tertiary Structure
• This structure arises from further folding of the secondary structure of the protein.
• H-bonds, electrostatic forces, disulphide linkages, and Vander Waals forces stabilize this
structure.
• The tertiary structure of proteins represents overall folding of the polypeptide chains,
further folding of the secondary structure.
• It gives rise to two major molecular shapes called fibrous and globular.
• The main forces which stabilize the secondary and tertiary structures of proteins are
hydrogen bonds, disulphide linkages, van der Waals and electrostatic forces of
attraction.

4. Quaternary Structure
• The spatial arrangement of various tertiary structures gives rise to the quaternary
structure. Some of the proteins are composed of two or more polypeptide chains
referred to as sub-units. The spatial arrangement of these subunits with respect to each
other is known as quaternary structure.
• The exact amino acid sequence of each protein drives it to fold into its own unique and
biologically active three-dimensional fold also known as the tertiary structure. Proteins
consist of different combinations of secondary elements some of which are simple
whereas others are more complex. Parts of the protein chain, which have their own
three-dimensional fold and can be attributed to some functions are called “domains”.
These are considered today as the evolutionary and functional building blocks of
proteins.
• Many proteins, most of which are enzymes contain organic or elemental components
needed for their activity and stability. Thus, the study of protein evolution not only gives
structural insight but also connects proteins of quite different parts of the metabolism.

Enzymes

These are proteins that act upon substrate molecules and decrease the activation energy
necessary for a chemical reaction to occur by stabilizing the transition state. This stabilization
speeds up reaction rates and makes them happen at physiologically significant rates. Enzymes
bind substrates at key locations in their structure called active sites. They are typically highly
specific and only bind certain substrates for certain reactions. Without enzymes, most metabolic
reactions would take much longer and would not be fast enough to sustain life.

Process of Enzyme and Substrate

The initial step occurs when an enzyme binds to a substrate to form an enzyme-substrate
complex. Increasing the concentration of a substrate will, increase the rate of reaction until it
reaches maximum velocity. After forming the enzyme-substrate complex, a product forms that
dissociates from the enzyme, and the enzyme is then ready to repeat the catalysis steps.

Models of Enzyme-Substrate Complex

1. The lock and key model - proposes that the shape and chemistry of the substrate are
complementary to the shape and chemistry of the active site on the enzyme. This means when
the substrate enters the active site, it fits perfectly, and the two binds together, forming the
enzyme-substrate complex.

2. The induced fit model - and it hypothesizes that the enzyme and the substrate don’t initially
have the precise complementary shape/chemistry or alignment, but rather, this alignment
becomes induced at the active site by substrate binding. Substrate binding to an enzyme is
generally stabilized by local molecular interactions with the amino acid residues on the
polypeptide chain.

There are four common mechanisms by which most of these interactions are formed and alter
the active site to create the enzyme-substrate complex: covalent catalysis, general acid-base
catalysis, catalysis by approximation, and metal ion catalysis.

• Covalent catalysis occurs when one or multiple amino acids in the active site transiently
form a covalent bond with the substrate. This reaction usually takes the form of an
intermediate through a nucleophilic attack of the catalytic residues, which helps stabilize
later transition states.

• General acid-base catalysis takes place when a molecule other than water acts as a
proton donor or acceptor. Water can be one of the proton donors or acceptors in the
reaction, but it cannot be the only one. This characteristic can sometimes help make
catalytic residues better nucleophiles, so they will more easily attack substrate amino
acids.

• Catalysis by approximation happens when two different substrates work together in the
active site to form the enzyme-substrate complex. A common example of this involves
water entering the active site to donate or receive a proton after a substrate has already
bound to form better nucleophiles that can form and break bonds easier.

• Metal ion catalysis involves the participation of a metal ion at the active site of the
enzyme, which can help make the attacking residue a better nucleophile and stabilize any
negative charge in the active site.

Inhibitors are regulators that bind to an enzyme and inhibit its functionality. There are three types
of models in which an inhibitor can bind to an enzyme: competitive, non-competitive, and
uncompetitive inhibition.

• Competitive inhibition occurs when the inhibitor binds to the active site of an enzyme
where the substrate would usually bind, thereby preventing the substrate from binding.
For enzymes obeying Michaelis-Menten kinetics, this results in the reaction having the
same max velocity but less affinity for the binding substrate.
 • Non-competitive inhibition occurs when the inhibitor binds to a site on the enzyme other
than the active site but results in a decreased ability of the substrate to bind to the active
site. The substrate is still able to bind in this model, but the active site functions less
effectively. The max velocity under non-competitive inhibition decreases, but the affinity
for substrate stays the same.

• Uncompetitive inhibition (also called anti-competitive inhibition) occurs when an

inhibitor binds only to the enzyme-substrate. This reaction usually occurs when there are
two or more substrates or products in a reaction. In uncompetitive inhibition, the max
velocity and binding affinity both decreases.

Factors affecting Enzyme Activity

 • The temperature: Each enzyme has an optimum temperature at which it works best. A
higher temperature generally results in an increase in enzyme activity. As the temperature
increases, molecular motion increases resulting in more molecular collisions. If, however,
the temperature rises above a certain point, the heat will denature the enzyme, causing it
to lose its three-dimensional functional shape by denaturing its hydrogen bonds. Cold
temperature, on the other hand, slows down enzyme activity by decreasing molecular
motion.

• The pH: Each enzyme has an optimal pH that helps maintain its three-dimensional
shape. Changes in pH may denature enzymes by altering the enzyme's charge. This
alters the ionic bonds of the enzyme that contribute to its functional shape.
• The concentration of enzyme: Assuming a sufficient concentration of substrate is
available, increasing enzyme concentration will increase the enzyme reaction rate.
• The concentration of substrate: At a constant enzyme concentration and at lower
concentrations of substrates, the substrate concentration is the limiting factor. As the
substrate concentration increases, the enzyme reaction rate increases. However, at very
high substrate concentrations, the enzymes become saturated with substrate and a
higher concentration of substrate does not increase the reaction rate.
• Cofactors and Coenzymes: Inorganic substances (zinc, iron) and vitamins
(respectively) are sometimes needed for proper enzymatic activity.

Redox Reactions of Enzymes

Oxidation and Reduction in Metabolism

• The transfer of electrons between molecules is important because most of the energy
stored in atoms and used to fuel cell functions is in the form of high-energy electrons.
The transfer of energy in the form of electrons allows the cell to transfer and use energy
incrementally; that is, in small packages rather than a single, destructive burst.
• Reactions that remove electrons from donor molecules, leaving them oxidized, are
oxidation reactions; those that add electrons to acceptor molecules, leaving them
reduced, are reduction reactions. Because electrons can move from one molecule to
another, oxidation and reduction occur in tandem. These pairs of reactions are called
oxidation-reduction reactions, or redox reactions.

Energy Transformation
ss from online meeting

Photosynthesis

• Jan Ingenhousz – The first man to discover photosynthesis

o In 1779, he observed that in the presence of light plants give off bubbles from
their green parts while, in the shade, the bubbles eventually stop. He identified
the gas as oxygen. He also observed that, in the dark, plants give off carbon
dioxide.
• “Photos” meaning light and “synthesis” meaning “putting together”
• 6CO2 + 6H20 --> C6H12O6 + 6O2 (Light Dependent Reaction)
• C6H12O6 + 6O2 --> 6CO2 + 6H20 + ATP (Light Independent Reaction)
• Takes place in the chloroplasts of a cell

Light Dependent Reaction

• Converts light energy into chemical energy

• Located in the thylakoid
• Uses sunlight, H2O, NADP+ and ADP
• Produces NADP, ATP and O2 (waste product)
• Utilizes Electron Transport Chain
o In photosystem II, the excited electron travels along a series of proteins. This
electron transport system uses the energy from the electron to pump hydrogen
ions into the interior of the thylakoid. A pigment molecule in photosystem I
accepts the electron.

Light Independent Reaction

 • Use stored chemical energy to “fix” CO2 and create a product that can be converted into
glucose
• Located in the Stroma
• Uses CO2, NADPH and ATP
• Produces NADP+, ADP, G3P (two G3P can be made into glucose; C6H12O6)
o The Calvin cycle has three stages.
▪ In stage 1 (Carbon Fixation), the enzyme RuBisCO incorporates carbon
dioxide into an organic molecule.
• 6 ATP → 6 ADP
▪ In stage 2 (Reduction), the organic molecule is reduced.
• 6 NADPH → 6 NADP+
▪ In stage 3 (Regeneration of RuBP), RuBP, the molecule that starts the
cycle, is regenerated so that the cycle can continue.
• 3 ATP → 3 ADP

Cellular Respiration

Glycolysis

• Glucose is converted into pyruvate with help of ATP

• C6H12O6 + 2 NAD+ + 2 Pi + 2 ADP → 2 Pyruvate + 2 NADPH + ATP
• Located in the Cytosol
• Uses glucose(C6H12O6), nicotinamide adenine dinucleotide (NAD+), phosphoglucose
isomerase (Pi) and adenosine diphosphate (ADP)
• Produces pyruvate, NADPH and ATP
o Step 1: breaks 1 molecule of glucose in half, producing 2 molecules of pyruvic
acid (a 3-carbon compound) NAD+ (nicotinamide adenine dinucleotide)
o Step 2: 2 NAD+; electron carrier accepts 4 high-energy electrons transfers them
to 2 NADH molecules and 2 H+ thus passing the energy stored in the glucose
o Step 3: 4 ADP added producing 4 ATP
o Step 4: 2 remaining pyruvic acids enter Krebs Cycle in presence of oxygen; IF no
oxygen another pathway is followed
• Glycolysis is a fast process
• Cells produce thousands of ATP molecules in a few milliseconds
• Glycolysis alone DOES NOT require oxygen

Kreb’s Cycle (Aerobic Respiration)

• Located in the Mitochondria

• 2nd stage of cellular respiration
• Named after Hans Krebs, British biochemist in 1937
• Here pyruvic acid is broken down into carbon dioxide in a series of energy-extracting
reactions
 • Citric acid is the 1st compound formed in this series of reactions, so Krebs is sometimes
called the Citric or Citric Acid Cycle.’
o Pyruvic acid enters from glycolysis; One carbon removed = CO2 formed
o NAD+ again changed to NADH
o CoA joins remaining 2 carbons = Acetyl-CoA
o Acetyl-CoA added to 4 carbon Compound = Citric acid (6-C)
o Citric acid broken down to 5-carbon then 4 carbon; more CO2 released
o Along the way more NADH and FADH2 formed
o One molecule of ATP also made
o 2 turns & 2 pyruvic acid (from glycolysis)
o Total Yield: 8 NADH, 2 FADH2, 2 ATP
• Carbon dioxide is exhaled (waste product)
• ATP can be used for cellular activities
• High-energy electrons (stored in NADH & FADH2) can be used to make huge amounts
of ATP in the presence of oxygen

Electron Transport Chain (Aerobic Respiration)

• Located in the Mitochondria Matrix

o Electrons from Krebs cycle is passed to electron transport chain by NADH &
FADH2
o At end of the chain an enzyme combines electrons from the electron chain with
H+ ions and oxygen to form water
o Each time 2 high-energy electrons transport down the electron chain, their
energy is used to transport H+ ions across the membrane
o H+ ions build up in intermembrane space it is now positively charged, other side
of membrane negatively charged
o Electrochemical gradient (chemiosmotic gradient) created for ATP synthase to
work
o ATP synthase converts ADP into ATP

Total Yield of Aerobic Cellular Respiration: 38 ATP

Fermentation (Anaerobic Respiration)

• Fermentation releases energy from food molecules in absence of oxygen

• In this process cells convert NADH to NAD+ by passing high-energy electrons back to
pyruvic acid
• Now glycolysis has NAD+ and can continue producing ATP
• There are 2 types of fermentation:
o Alcoholic fermentation
o Lactic acid fermentation

Alcoholic Fermentation
 • Yeast and a few other microorganisms use alcoholic fermentation, forming ethyl alcohol
and carbon dioxide as wastes
• pyruvic acid + NADH →ethyl alcohol + CO2 + NAD+

Lactic Acid Fermentation

• Many cells convert accumulated pyruvic acid from gycolysis to lactic acid; lactic acid
fermentation regenerates NAD+ so glycolysis can continue
• pyruvic acid + NADH →lactic acid + NAD+
• When your body cannot supply enough oxygen to muscle tissues during exercise, this is
produced
• Without oxygen the body is unable to produce all the ATP it requires, so lactic acid
fermentation takes over

Quick Energy

• ATP in muscles only lasts a few seconds

• ATP from lactic acid fermentation lasts about 90 seconds
o this then creates a by-product (lactic acid) which the body must get rid of, the
body releases it by panting heavily (intake of oxygen)

Long-Term

• Energy-exercise lasting longer than 90 seconds utilizes cellular respiration to generate a

continuous supply of ATP
• Cellular respiration releases energy slower than fermentation, thus athletes can pace
themselves
• body stores energy in muscles and tissues in the form of glycogen(carbohydrate)
o stores of glycogen usually last for 15-20 minutes of activity, then the body starts
to break down other molecules like fat for energy

AEROBIC VS. ANAEROBIC RESPIRATION: A COMPARISON

• Advantages of Aerobic Respiration

o Major advantage →more energy released
o Enough energy to produce up to 38 ATP
• Advantages of Anaerobic Respiration
o Let organisms live in places where there is little or no oxygen
o Quickly produces ATP

RELATIONSHIP BETWEEN CELLULAR RESPIRATION AND PHOTOSYNTHESIS

Equation for Cellular Respiration: 6O2 + C6H12O6→6CO2 + 6H2O + energy (ATP)
Equation for Photosynthesis: 6CO2 + 6H2O + energy (sunlight) →6O2 + C6H12O6