BIOMOLECULES

BIOMOLECULES
• It is a chemical compound found in living organisms.

• Building blocks of life, essential for the functioning of living

organisms.

• It is composed of carbon, hydrogen, oxygen, nitrogen, sulphur and

phosphorus
Types of Biomolecules

• Carbohydrates

• Proteins

• Nucleic acids

• Lipids
PROPERIES AND FUNCTION
OF CARBOHYDRATES
CARBOHYDRATES
• Components that make up
carbohydrate biomolecules
• Empirical formula for
carbohydrates-(CH2O)n .
• Energy for our body.
 Foods That have Carbohydrates
• Grains, such as bread, noodles, pasta, cereals, and rice
• Fruits, such as apples, bananas, berries, mangoes, melons, and oranges
• Dairy products, such as milk and yogurt
• Legumes, including dried beans, lentils, and peas
• Snack foods and sweets, such as cakes, cookies, candy, and other desserts
• Juices, regular sodas, fruit drinks, sports drinks, and energy drinks that contain
sugar
• Starchy vegetables, such as potatoes, corn, and peas
Classification of Carbohydrates
Monosaccharides
• Simple sugars with a free ketone
or aldehyde group.
• can’t be hydrolyzed anymore.
• CnH2nOn or Cn (H2O) n is their
chemical formula.
• Ex-Glucose, fructose, galactose,
glycerose, ribose, and ribulose.
Disaccharides
• Hydrolyze into two molecules of the same or distinct
monosaccharides.
• Oxide bond- Glycosidic linkage.
• Examples:
1. Sucrose: Glucose and Fructose
2. Lactose: Galactose & Glucose
3. Maltose: Glucose & Glucose
Oligosaccharides
• Hydrolyzed, they break down into two to ten molecules of
monosaccharides.
• Oligosaccharides that break down into three or four monosaccharide
molecules.
• Disaccharides have the chemical formula Cn (H2O)n-1,
• Trisaccharides have the chemical formula Cn (H2O)n-2, and so on.
• Examples:Sucrose, maltose, lactose, raffinose, and stachyose .
Polysaccharides
• Long monosaccharide molecules are linked together by a glycosidic
linkage.
• Examples: Cellulose & starch
• It is made up of β-D-glucose units linked together by a glycosidic
bond between C1 of one glucose unit and C4 of the next.
• Starch: Amylose and amylopectin are two forms of polymeric chains
found in them.
• Amylose has a linear structure
with α1–4 glycosidic links.

• Amylopectin has a branching

structure with α1–4 and α1–6
glycosidic linkages
Functions of Carbohydrates

• Carbohydrates are the major or principal energy sources in our

bodies.
• They have a role in fat metabolism as well.
• Carbohydrates keep you out of ketosis.
• This is a kind of connective tissue.
• Carbohydrates keep the body’s digestive system running smoothly.
• Carbohydrate fibres can help reduce blood cholesterol levels.
• Because carbohydrates prevent protein from being burnt, they are needed to
construct and repair.
• Carbohydrates provide the central nervous system with energy.
• They come in a variety of forms, including sugar, glucose, starch, and fibre.
Sources of Carbohydrates
• Many fruits contain simple sugars in the form of fructose.
• All dairy products include galactose.
• Lactose may be found in large quantities in milk and other dairy
products.
• Maltose may be found in a variety of foods, including cereal, beer,
potatoes, processed cheese, and pasta.
• Sucrose is derived from sugar and honey, both of which include trace
quantities of vitamins and minerals.
 Importance of Carbohydrates
• Carbohydrates aid in metabolism
• Plant cellulose is also utilised in the production of papers, textiles, and wood
for building.
• Photosynthesis
• Main sources of energy.
• Plants store starch, which includes thousands of glucose units, as an energy
source.
• Glycogen breaks down into simple glucose molecules during stress and
muscle exercise.
• Arthropods’ exoskeletons are composed of chitin, a complex carbohydrate
Importance of Carbohydrates in all Living
Organisms
• Carbohydrates are necessary for all living things in our environment to survive.
• Sugar molecules such as ribose and deoxyribose make up the majority of genetic materials (DNA and
RNA) in living organisms.
• ATP (Adenosine Triphosphate), the most important energy-transfer molecule in living beings.
• Green plants convert carbon dioxide into organic substances such as sugars, which supply energy to the
plants.
• In the soil, certain carbohydrates enhance seed germination and root elongation.
• Some rare sugars are employed in the pharmaceutical sector to make blood sugar controlling
medications.
• Anti-inflammatory properties of some complex oligosaccharides and oligonucleotides aid in the
treatment of cancer.
• Antiviral medicines containing nucleoside analogues of uncommon sugars are used to treat HIV and
HCV.
NUCLEIC ACID
Nucleic acid

• Nucleic acids are macromolecules that are found in every living cell,

• End-to-end polymerisation of a vast number of units called nucleotides

linked by phosphodiester linkages forms these lengthy strands.

• The word “nucleic acid” is used to describe specific big molecules

found in cells.
 Properties of Nucleic Acid
• Nucleotides
• Two forms of nucleic acids.
• A nucleotide - heterocyclic base, or nitrogenous base, is one, a monosaccharide pentose sugar is another, and
phosphoric acid, or phosphate group, is the third.
• The nitrogenous bases are made up of one or two heterocyclic rings that include nitrogen atoms. Adenine (A),
guanine (G), uracil (U), cytosine (C), and thymine (5-methyl uracil) are the five bases (T).
• Adenine and guanine are substituted purines with two heterocyclic rings, whereas uracil, cytosine, and thymine
are substituted pyrimidines with three heterocyclic rings (1 heterocyclic ring).
• DNA has the nitrogenous bases A, T, G, and C, whereas RNA has the nitrogenous bases A, U, G, and C.
• Polynucleotides either include beta-ribose sugar (in RNA) or beta 2′ deoxyribose sugar (in DNA) (in DNA).
• Nucleosides: Sugar + Base
• Nucleotides are made up of three parts: base, sugar, and phosphate.
• The backbone of DNA strands is made up of phosphodiester linkages, which are sugar and phosphate residues.
• Due to the presence of phosphate groups, they are acidic and negatively charged
Functions of Nucleic Acids
• Nucleic acids are genetic material for all living cells, meaning they
pass on hereditary characteristics from one generation to the next.
• Nucleic acid can also determine an organism’s phenotypic.
• Some nucleic acids, such as ribozymes, may have enzymatic activity.
• Nucleic acids play a role in protein production, either directly or
indirectly.
Structure of Nucleic Acid
• The nucleotide is a tiny unitary structure made up of phosphodiester
links that connect nucleic acids.
Each nucleotide comprises:
• A Nitrogen base
• A Pentose sugar
• Phosphoric acid
• An N-glycosidic linkage connects a pentose sugar to a nitrogenous
base to form a nucleoside
Bonds between Different Units of Nucleotides

• N–glycosidic linkage: To generate a nucleoside, a nitrogenous base is

attached to the pentose sugar via a N– glycosidic linkage. Purine
nucleosides feature a 1’–9′ glycosidic bond (sugar carbon 1′, A/G
nitrogen 9′). The 1’–1′ linkage (sugar carbon 1′ and 1′ nitrogen of T/C)
is found in pyrimidine nucleosides.
• Phosphodiester linkage: A matching nucleotide is generated when a
phosphate group is attached to the 5′–OH of a pentose sugar of a
nucleoside via phosphodiester linkage. A dinucleotide is made up of
two nucleotides joined together by a 3′–5′ phosphodiester bond.
Types of Nucleic Acids

• Deoxyribonucleic acid (DNA)

• Ribonucleic Acid (RNA)

DNA
• Occurrence: DNA is mostly present in the chromosomes of plant and
animal cells’ nuclei.
• It’s found in mitochondria and chloroplasts as well.
• It’s found in circular and supercoiled chromosomes in prokaryotes’
cytoplasm.
• Eukaryotes with proteins such as histones and protamine
Structure of DNA( Double Helical Model)

• Rosalind Franklin
• Maurice Wilkins
• Watson & Crick
Model of DNA
• In 1953
• A right-handed helical spiral is formed
by each chain of DNA
• Phosphodiester bond
• Antiparallel Direction 5’→3′ direction
and the other coming from the 3’→5′
direction.
• The nitrogenous bases
• chains are complementary
• DNA has a 2nm consistent thickness.
• The pitch of the helix is 3.4nm for each
round of the double helix
• Each turn comprises around 10 base
pairs
• The helix’s backbone is made up of
sugar and phosphate, with bases aligned
along the axis
• The 5' and 3' mean "five prime"
and "three prime", which indicate
the carbon numbers in the DNA's
sugar backbone.
• The 5' carbon has a phosphate
group attached to it and the 3'
carbon a hydroxyl (-OH) group.
• This asymmetry gives a DNA
strand a "direction".
RNA
• RNA is a single-stranded nucleic acid found in a few viruses, such as
retroviruses and viroids, as genetic material.

• Occurrence: The majority of RNA is located in the cytoplasm of

cells. The nucleolus and nucleoplasm both contain it.
 Structure of RNA
• The single RNA strand is folded back on itself,
generating hairpin-like structures fully or in parts.
• In some plant viruses, the genetic material is double-
stranded but non-helical RNA.
• Each strand of RNA is made up of a large number of
ribonucleotides that are bonded together by
phosphodiester linkages.
• Adenine and uracil (A-U) form a pair, and guanine
and cytosine form a pair (G-C).
• Messenger RNA, ribosomal RNA, and transfer RNA
are the three kinds of RNA.
Types of RNA
 Difference between DNA and RNA
DNA RNA

It contains deoxyribose sugar. It contains ribose sugar.

It is related to chromosomes and can be found in the cytoplasm, nucleolus,

It can be present in the nucleus, mitochondria, and chloroplast chromosomes.
and nucleoplasm.

Double-stranded structure. Single-stranded structures generally except a few viruses.

Adenine, guanine, cytosine, and thymine are the nitrogenous bases found. Adenine, guanine, cytosine, and uracil are the nitrogenous bases found.

A long molecule with high molecular weight. A relatively short molecule with low molecular weight.

Purines and pyrimidines occur in equal proportion Purines and pyrimidines do not occur in equal proportion.

DNA is the hereditary material. Only a few viruses and viroids have RNA as their genetic material.
 PROTEINS
• Proteins are large-sized
heteropolymeric
macromolecules having one
or more polypeptides (chains
of amino acids).
• Proteins are body builders of
organisms.
 Types of Proteins
On the Basis of Shape:
1. Fibrous Proteins
• They are thread like proteins which may
occur singly or in groups.
• They are tough, nonenzymatic and structural
proteins. Fibrous proteins generally possess
secondary structure.
• They are insoluble in water. Keratin of skin
and hair is such a fibrous protein.
• Ex: myosin of muscles and elastin of
connective tissue.
2. Globular Proteins
• They are rounded in outline.
• Contractibility is absent.
• Final structure is tertiary or quaternary.
• Globular proteins may be enzymatic or
non-enzymatic.
• Smaller globular proteins are mostly
soluble in water.
• They are not coagulated by heat, e.g.,
histones
b) On the Basis of Function:

1. Enzymatic Proteins: They are proteins which function as enzymes, either

directly (e.g., amylase, pepsin) or in conjunction with a non-protein part called
cofactor (e.g., dehydrogenases). Enzymatic proteins are usually globular in
shape.
2. Structural or Protoplasmic Proteins: They form part of cellular structures
and their products, e.g., colloidal complex of protoplasm, cell membranes,
contractile proteins, structural proteins of hair and nails. In shape, structural
proteins can be globular or fibrous.
3. Reserve or Storage Proteins: They occur as food reserve mostly in seeds, eggs
or milk. Storage proteins are usually globular. Depending upon their solubility,
reserve pro-teins are of four types— albumins, globulins, prolamines and
glutelins.
Structure of Proteins:
• A polypeptide chain is synthesized on the ribosome as a linear
sequence of amino acids.
• Just after the synthesis, the newly synthesized (nascent) polypeptide
folds into a specific three dimensional shape called conformation.
• The conformation adopted by polypeptide to perform the biological
activity is called native conformation
Four levels of organizations

• Primary

• Secondary

• Tertiary

• Quaternary
A. Primary (1°) Structure
• Primary structure of a protein means the
sequences amino acid residues of its
polypeptide chain (s) which read in N-
terminus → C-terminus direction.
• It is the 1st level of organization of
protein determined by the codons of
mRNA or cistron of DNA.
• The 1° structure is stabilized by the
peptide bonds as well as and disulfide
bonds between cysteine residues
Secondary (2°) structure
• Protein 2° structure refers to the spatial
arrangement of backbone atoms of
polypeptides without considering the
conformations of side chains.
• The common types of secondary structures
are α-helix and β-pleated sheet.
• The α-helix formation is favoured by
alanine, leucine, glutamate and methionine
residues, whereas
• β- sheet is favoured by valine, isoleucine
and tyrosine residues.
(i) α-Helix
• The backbone atoms of a polypeptide
chain tightly coiled in a right-handed
manner to form many rod-like structures
at intervals called a-helices.
• The length of each helix usually varies
from 1.7-4.0 nm.
• In a α-helix, 3.6 amino acid residues
present per turn covering a distance
(pitch) of 0.54 nm (5.4A)
(ii) β- pleated sheet
• About 2-15 polypeptide chains come together to form a β-pleated
sheet.
• The β-pleated sheet is stabilized by hydrogen bonds between CO- and
NH groups in different polypeptide chains;

β- pleated sheet is of 2 types –

1. Parallel β-sheet – Adjacent chains run in the same direction e.g. β-
keratin.
2. Antiparallel β-sheet – Adjacent chains own in opposite direction
e.g. silk fibroin
Tertiary (3°) Structures
• Protein tertiary structure refers to
the 3-D structure of an entire
polypeptide showing the folding
of secondary and super secondary
structures to form a compact
globular structure.
• The 3° structure is stabilized by
hydrogen bonds, ionic bonds,
hydrophobic interactions, Vander
Walls force, and London
dispersion forces
D. Quaternary (4°) Structure
• It is the fourth level of structural
organization exhibited only in
oligomeric proteins.
• A protein’s quaternary structure refers
to the spatial arrangement of its
polypeptide subunits or protomers.
• In a 4° structure the subunits may or
may not be identical, and stabilized by
non covalent bonds, e.g.,
Haemoglobin.
FUNCTION OF PROTEINS
• Proteins are essential biomolecules that are critical to life and to perform various activities.
• Many proteins act as catalysts that enhance the rate of chemical reactions in various metabolic pathways.
• The fibrous proteins are a component of various tissues holding the skeletal elements together like
collagen, which is a structural unit of connective tissues.
• The nucleoproteins serve as carriers of genetic characters and hence govern the inheritance of traits.
• Proteins also perform transport functions that regulate the transport of many compounds in and out of the
cells and accumulate inside at much higher concentrations than expected from diffusion alone.
• Various protein hormones regulate the growth of plants and animals, besides controlling many other
physiological functions.
• Blood plasma has multiple soluble proteins that can be used for the treatment of shock produced by severe
injuries and operations.
• Interferons are regulatory glycoproteins produced by many eukaryotic cells in response to virus infection,
endotoxins, antigenic stimuli, and many parasitic organisms.
• Peptides from humans called defensins are antibiotic in nature.
 LIPIDS
• Lipids are heterogeneous group of water
insoluble compounds which are oily or
greasy in consistency but soluble in non-
polar solvents like ether, chloroform,
benzene etc.
• Lipids are composed of C, H, O, like
carbohydrates but poor in oxygen and
therefore require more oxygen for
oxidation to release energy
Characteristics of Lipids
• Lipids consist of fats, oils, hormones, and certain components of membranes that
are grouped together because of their hydrophobic interactions.
• The lipids are essential constituents of the diet because of their high energy value.
• These are also essential for the fat-soluble vitamins and the essential fatty acids
found with the fat of the natural foodstuffs.
• Fats combined with proteins (lipoproteins) are essential constituents of the cell
membranes and mitochondria of the cell.
• Lipids occur naturally in living beings like plants, animals, and microorganisms
that form various components like cell membranes, hormones, and energy storage
molecules.
• Lipids exist in either liquid or non-crystalline solids at room temperatures and are
colorless, odorless, and tasteless.
• These are composed of fatty acids and glycerol.
 LIPIDS STRUCTURE
• Lipid monomers are glycerol and fatty acids.
• Fatty acids are a type of lipids that consists of long
hydrocarbon chains with a carboxyl group (COOH) at one
end.
• In lipids, such as triglycerides, the glycerol molecule
function as a backbone. Glycerol molecule consists of three
carbon atoms with a hydroxyl group attached to them.
• Glycerol are linked to the fatty acid through ester bonds,
that forms triglycerides.
• The hydrocarbon chains of fatty acids are hydrophobic, that
is repelling water.
• In lipids like phospholipids, a hydrophilic phosphate group
is attached to the glycerol, while the fatty acid chains remain
hydrophobic, resulting in an amphipathic molecule.
 Classification of Lipids
1. Nonsaponifable Lipids
• These lipids cannot be hydrolyzed or saponified using alkaline hydrolysis.

• They are often complex and structurally diverse.

• Examples of nonsaponifiable lipids include cholesterol (a steroid) and carotenoids (found in pigments like
beta-carotene).

2. Saponifiable Lipids
• Saponifiable lipids can be hydrolyzed or saponified using alkaline hydrolysis.
• They consist of fatty acids and other components that can be broken down into simpler compounds.

• The most common saponifiable lipids are triglycerides (fats and oils), which consist of glycerol and fatty
acids esterified together.
• When saponified, these lipids break down into glycerol and fatty acids.
• Saponifiable are further divided into Polar and non-Polar lipids.
• Polar Lipids: Polar lipids are also known as
amphipathic lipids because they have both hydrophilic
(water-attracting) and hydrophobic (water-repellent)
regions within their molecular structure. Examples of
polar lipids include phospholipids and glycolipids.

• Non- Polar Lipids: Non-polar lipids are hydrophobic

and do not have a significant hydrophilic component in
their structure. They are primarily involved in energy
storage and insulation. For example, Triglycerides (fats
and oils).
Types of Lipids
• Simple Lipids: Simple lipids are triglycerides, esters of fatty acids, and wax esters.
The hydrolysis of these lipids gives glycerol and fatty acids.

• Complex Lipids: Complex or compound lipids are the esters of fatty acids with
groups along with alcohol and fatty acids. Examples are Phospholipids and
Glycolipids.

• Derived lipids: Derived lipids are the hydrolyzed compounds of simple and
complex lipids. Examples are fatty acids, steroids, fatty aldehydes, ketone bodies,
lipid-soluble vitamins, and hormones.
 Simple Lipids
Simple lipids are classified into Triglycerides and Waxes.
1. Fats: Fatty acids join with glycerol via ester bonds.
2. Waxes: Fatty acid jig with a large molecular weight monohydric alcohol
with an ester bond.

Triglycerides
1. Triglycerides are the most common type of simple lipids.
2. They consist of glycerol molecules linked to three fatty acid chains through
ester bonds.
3. Triglycerides are found in adipose tissue (body fat) and serve as a long-term
energy reserve.
4. They are the constituents of fats and oils. Lipids that are solid at room
temperature are fats, and lipids that are liquid at room temperature are oils.
Glycerol
• It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic.
The glycerol backbone is found in those lipids known as glycerides. It is a
simple polyol compound.
 Precursor Lipids

• Precursor lipids are the building blocks from which other lipid molecules are synthesized
or derived. They serve as starting points for the biosynthesis of more complex lipids.
Some examples are- Fatty acids, Glycerol, and alcohol.

• Fatty Lipids: Fatty acids are carboxylic acids; they are long chains of hydrocarbons with
a carboxylic group at the end. Fatty acids are an important component of lipids, they are
the building blocks of fat in the body.

There are two types of fatty acids,

1. Saturated fatty acids and

2. Unsaturated fatty acids.

Saturated Fatty Acids
• It consists of single C-C single bonds. These
molecules fit closely together in a regular pattern and
have strong attractions between fatty acid chains.
These fatty acids have high melting points, which
makes them solid at room temperature.
• Examples of saturated fatty acids are palmitic acid
and stearic acid.
Unsaturated Fatty Acids
• Unsaturated fatty acids are fatty acids that consist of
one or more C=C double bonds. An unsaturated fatty
acid is divided into two types.
1. Mono polyunsaturated fatty acids: Example:
oleic acid.
2. Polyunsaturated fatty acids: Example: linoleic
acid.
 Complex Lipids
• They contain additional molecules, such as phosphates,
carbohydrates, proteins, fatty acids and glycerol.
• Complex lipids are involved in various biological functions, including cell
structure, energy storage, and cell signalling.
• Examples of complex lipids are Phospholipids and glycolipids.

Phospholipids
• These are constituents of cellular membranes.

• An ester is formed when a hydroxyl reacts with a carboxylic acid and loses
H2O.

• Phospholipids, also known as phosphatides, are classes of lipids whose

molecule has a hydrophilic head and two hydrophobic tails. A head
containing a phosphate group and tails derived from fatty acids joined by a
glycerol molecule. They serve as emulsifiers.
 Types of phospholipids
• Glycerophospholipids: Glycerophospholipids are the class of phospholipids
containing glycerol as alcohol, two fatty acids, and phosphate. It is the most
abundant lipid in the cell membrane.

• Sphingophospholipids: Sphingophospholipids are the class of phospholipids

containing sphingosine as alcohol. It produces ceramide by an amide linkage to a
fatty acid. Ceramide is an important component of skin. It acts as a second
messenger to regulate programmed cell death.
Glycolipid
• It is a structural lipid, an essential part of the cell membrane.
• They are lipids with a carbohydrate attached by a glycosidic bond.
• They act as receptors at the surface of the red blood cell. It helps in the
determination of an individual blood group.
• It has an important role in maintaining of the stability of the cell membrane.
• It kills pathogens to help the immune system of the body.
• Cerebrosides and Gangliosides are the two types of Glycolipids.
 Derived Lipids
Derived lipids are the hydrolyzed compounds of simple and complex lipids.

Examples are fatty acids, steroids, fatty aldehydes, ketone bodies, lipid-soluble vitamins, and hormones.

• Steroids
1. Steroids are found in the cell membrane and have fused ring structures.

2. Many steroids have -OH functional groups, they are also hydrophobic and insoluble in water.

3. All the steroids have 4 linked carbon rings and most of them have a short tail. Steroids also act as hormones in the body.

• Sterols
1. Sterols are solid steroid alcohols that are widely present in plants and animals such as cholesterol and ergosterol.

2. They are the subgroup of steroids, which naturally occur in most eukaryotes

3. They are found in animal products. They are used to make bile for digestion in the body.

4. Sterols can have greater than half of the membrane lipid content in cells and they are known to alter membrane structure and fluidity.
• Carotenoids
1. Carotenoids are lipid-soluble compounds.
2. They are pigments that are mainly responsible for the yellow and red colors
of plant and animal products.
3. Carotenoids consist of carotenes and xanthophylls.
4. A class of hydrocarbons is carotenes and its oxygenated derivatives are
xanthophylls.
5. They give color to many fruits and vegetables.
6. They have antioxidant and anti-inflammatory properties for humans.
7. Carotenoids are important for the health of the human eye.
 Role of Fats
Fats play an essential role in the body, including:
• Fats help our body by absorbing and transporting important fat-soluble vitamins.

• They are an important source of essential fatty acids.

• They insulate and protect our vital body organs.
• Fats produce energy in the form of carbohydrates.

• Fats are the structural component of cells.

• They help the body produce and regulate hormones.
• Fats support cell growth.
• They maintain our core temperature.
• Maintains blood pressure and cholesterol.
 Lipids Function
Functions of lipids are mentioned below:

• Lipids, like adipose tissue, act as insulators and help to maintain body temperature by reducing heat loss.

• Lipids, especially triglycerides, act as energy storage in organisms, providing a reserve of metabolic fuel.

• Phospholipids form the lipid bilayers of cell membranes and regulate the passage of molecules in and out of cells.

• Protecting the plant leaves from direct heat and drying.

• Steroid hormones, derived from cholesterol, play vital roles in regulating various physiological processes, including
metabolism, growth, and reproduction.

• It acts as the structural component of the body and also acts as the hydrophobic barrier.

• In plants, lipids can be stored as oils in seeds, providing a source of energy for germination and early growth.

• Lipids form waterproofing structures, such as the waxy cuticle on plant leaves or the oil on the feathers of water birds.

• It provides color to many fruits and vegetables with the presence of carotenoid pigment.
ENZYMES
 ENZYMES
• An enzyme is a protein biomolecule that acts
as a biocatalyst by regulating the rate of
various metabolic reactions without itself
being altered in the process.

• Enzymes are biological catalysts

• Enzymes are proteins that are prone to

damage and inactivation.

• Enzymes are also highly specific and usually

act on a specific substrate of specific reactions
 Structure of Enzymes

• All enzymes are proteins composed of amino acid chains linked together by
peptide bonds. This is the primary structure of enzymes.

• All enzymes have a highly specific binding site or active site to which their
substrate binds to produce an enzyme-substrate complex.

• The three-dimensional structures of many proteins have been observed by x-ray

crystallography
 Active site of enzymes
• Enzymes are much larger than the substrate
• Specific regions or sites on the enzyme for binding with the substrate.
Active site present in their molecule possesses some common features ;
1. The active site of an enzyme is a relatively small portion within an
enzyme molecule.

2. The active site is a 3-dimensional entity made up of groups that come

from different parts of the linear amino acid sequence.

3. The arrangement and orientation of atoms in the active site are well
defined and highly specific, which is the cause of the marked
specificity of the enzymes. However, in some cases, the active site
changes its configuration in order to bind a substance.

4. The interactions or forces between the active site and the substrate
molecule are relatively weak.

5. The active sites in the enzyme molecules are mostly present in

grooves or crevices from where large quantities of water are excluded.
 1. Ribonuclease (RNase)
• Ribonuclease is a small globular protein secreted by the pancreas into
the small intestine, where it is involved in the catalysis of the
hydrolysis of certain bonds in ribonucleic acids present in ingested
food.

• This enzyme protein consists of a single polypeptide chain of 124

amino acid residues with lysine at the N-terminal and valine at the C-
terminal.

• About 25% of the segments are in α-helix structure while the rest are
β-sheets.

• Besides, there are eight cysteine residues, thus apparently forming

four disulfide linkages that support the tertiary structure of the
protein.

• The active site is present in the depression at the middle of the chain
and the residues forming the active site are 6-8, 11, 12, 41, 42, 46-48,
and 117-119.
 2. Lysozyme
• Lysozyme is another small globular protein that is present in tears,
nasal mucus, gastric secretions, milk, and egg white.
• The enzyme lysozyme is consists of 129 amino acids linked together
to form the primary structure, and the first amino acid is lysine.
• The enzyme has about 12% β-conformation and 40%-α helical
segments.
• Lysozyme has a compactly-folded conformation with most of its
hydrophobic R groups inside the globular structure, away from
water, and its hydrophilic R groups outside, facing the aqueous
medium.
• The active site has six subsites that bind various substrates or
inhibitors, and the amino acid residues located at the active sites are
35, 52, 59, 62, 63, and 107.
 3. Chymotrypsin
• Chymotrypsin is a mammalian digestive enzyme produced in the
small intestine that catalyzes the hydrolysis of proteins.

• Chymotrypsin is highly selective in its action as it catalyzes the

hydrolysis of only those peptide bonds that are present on the
carboxyl side of amino acids with aromatic or bulky hydrophobic R
groups.

• A molecule of chymotrypsin consists of 3 short polypeptide chains of

13, 131, and 97 amino acid residues respectively, supported by two
interchain disulfide bonds.

• The secondary structure of chymotrypsin consists of several

antiparallel β pleated sheet regions and a little α helical structure.
 Enzyme-substrate complex
• The enzyme-substrate complex is a transitional molecule formed after the substrate
binds with the enzyme.

• The formation of the enzyme-substrate complex is important for several reasons.

The most important and notable reason is that the substrate binds with the enzyme
temporarily and the enzyme is set free once the reaction is complete.

• This allows a single enzyme molecule to be used millions of times, and thus, only a
small amount of enzyme is required in each cell.

• Another advantage of an enzyme-substrate complex is the reduction in the free

energy (activation energy) required for the substrate to rise into the high-energy
transition state.
 Enzyme specificity
1. Absolute specificity

• Some enzymes are capable of acting on only one substrate, and an example of this is
the enzyme urease that acts only on urea to produce ammonia and carbon dioxide.

2. Group specificity

• Other enzymes catalyze all reactions of a structurally related group of compounds.

• It is observed in lactic dehydrogenase (LDH) that catalyzes the interconversion of

pyruvic acid and lactic acid along with a number of other structurally related
compounds.
• 3. Optical specificity
• Another important form of specificity is seen in some enzymes where a certain
enzyme will react with only one of the two optical isomers of a compound.
• The oxidation of the D-amino acids to the corresponding keto acids by amino acid
oxidase is an example of optical specificity.
• Among the enzymes that exhibit optical specificity, some might interconvert the
two optical isomers of a compound. An example of this is alanine
racemase that catalyzes the interconversion between L- and D-alanine.
• 4. Geometrical specificity
• Geometrical specificity is observed in some enzymes exhibit specificity towards
the cis and trans forms.
• An example of this is the enzyme fumarase that catalyzes the interconversion of
fumaric and malic acids.
 Factors affecting enzyme activity

• Temperature: Raising temperature generally

speeds up a reaction, and lowering
temperature slows down a reaction.
However, extreme high temperatures can
cause an enzyme to lose its shape (denature)
and stop working.
• pH: Each enzyme has an optimum pH
range. Changing the pH outside of
this range will slow enzyme activity.
Extreme pH values can cause
enzymes to denature.
• Enzyme concentration: Increasing
enzyme concentration will speed up the
reaction, as long as there is substrate
available to bind to. Once all of the
substrate is bound, the reaction will no
longer speed up, since there will be
nothing for additional enzymes to bind to.
• Substrate concentration: Increasing
substrate concentration also increases
the rate of reaction to a certain point.
Once all of the enzymes have bound,
any substrate increase will have no
effect on the rate of reaction, as the
available enzymes will be saturated
and working at their maximum rate.
 Properties of Enzymes
• Enzyme molecules are large, and because of their large size, the enzyme molecules possess meager rates of
diffusion. As a result, enzymes form colloidal systems in water.

• Enzymes act catalytically and accelerate the rate of chemical reactions occurring in biological systems and
involving biological substrate.

• Most enzymes also do not participate in the reactions they catalyze. Similarly, some enzymes that are involved in
the reaction are recovered without undergoing any qualitative or quantitative change at the end of the reaction.

• Most enzymes are highly specific in their action.

• Being proteinaceous in nature, the enzymes are susceptible to heat. The rate of an enzyme action increases with
the rise in temperature; the rate being frequently increased 2 to 3 times for a rise in temperature of 10ºC.

• The enzymes catalyze the reversion of the reactions they catalyze.

• Enzymes are also pH sensitive as the pH of a medium will affect the efficiency of an enzyme and their activity is
maximum at a specific pH.
 Classification of Enzymes
1. Oxidoreductases

• Catalyze oxidation-reduction reactions where electrons are transferred.

• These electrons are usually in the form of hydride ions or hydrogen atoms.

• The most common name used is a dehydrogenase and sometimes reductase is used.

• An oxidase is referred to when the oxygen atom is the acceptor.

• e.g. pyruvate dehydrogenase, catalysing the oxidation of pyruvate to acetyl coenzyme

A.
2. Transferases
• Catalyze group transfer reactions.
• The transfer occurs from one molecule that will be the donor to another molecule
that will be the acceptor.
• Most of the time, the donor is a cofactor that is charged with the group about to be
transferred.
• Example: 1)Hexokinase used in glycolysis.

• Transaminase, which transfers an amino group from one molecule to another.

3. Hydrolases

• Catalyze reactions that involve hydrolysis.

• It usually involves the transfer of functional groups to water.

• When the hydrolase acts on amide, glycosyl, peptide, ester, or other bonds, they
not only catalyze the hydrolytic removal of a group from the substrate but also a
transfer of the group to an acceptor compound

• For example: Chymotrypsin.

• For example, the enzyme pepsin hydrolyzes peptide bonds in proteins

4. Lyases

• Catalyze reactions where functional groups are added to break double bonds in
molecules or the reverse where double bonds are formed by the removal of
functional groups.

• e.g. Aldolase (an enzyme in glycolysis) catalyzes the splitting of fructose-1, 6-

bisphosphate to glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.
5. Isomerases

• Catalyze reactions that transfer functional groups within a molecule so that

isomeric forms are produced.

• These enzymes allow for structural or geometric changes within a compound.

• For example: phosphoglucose isomerase for converting glucose 6-phosphate to

fructose 6-phosphate. Moving chemical group inside same substrate.
6. Ligases

• They are involved in catalysis where two substrates are ligated and the formation
of carbon-carbon, carbon-sulfide, carbon-nitrogen, and carbon-oxygen bonds due
to condensation reactions.

• These reactions are coupled to the cleavage of ATP.

• For example, DNA ligase catalyzes the joining of two fragments of DNA by
forming a phosphodiester bond.
 Functions/ Biological roles of Enzymes
1. Enzymes like kinases and phosphatases are important for cell regulation and signal transmission.
2. Different enzymes are produced throughout the body for the regulation of reactions involved in various
metabolic pathways.
3. The activation and inhibition of enzymes resulting in a negative feedback mechanism adjust the rate of synthesis
of intermediate metabolites according to the demands of the cells.
4. They also catalyze Post-translational modifications involving phosphorylation, glycosylation, and cleavage of
the polypeptide chain.
5. Some enzymes are also involved in the regulation of enzyme levels by changing the rate of enzyme degradation.
6. Since a tight regulation of enzymes is essential for homeostasis, any changes in the enzyme structure and
production might result in diseases.
7. Enzymes synthesized in various organisms are also utilized in various industries for wine production, cheese
production, bread whitening, and designing fabrics.
 Enzyme-catalyzed reactions
1. Inversion of cane sugar

• Invertase converts cane sugar into glucose and fructose.

invertase
C12H22O11 + H2O → C6H12O6 + C6H12O6
(sucrose/ cane sugar) (glucose) (fructose)

2. Degradation of urea

• Urease catalyzes the degradation of urea into ammonia and carbon dioxide.

urease
(NH2)2CO + H2O → 2NH3 + CO2
(urea) (ammonia) (carbon dioxide)
3. Isomerization reaction
• Isomerase enzyme catalyzes the conversion of glyceraldehydes-3-phosphate into
dihydroxy-acetone phosphate.

4. Protein digestion
• Pepsin converts proteins into shorter polypeptides.
pepsin
Proteins → polypeptides
 VITAMINS
• Vitamins are a group of organic
compounds that are extremely necessary
and essential for normal growth and
functioning of the human body.

• They are required in very small

quantities but cannot be synthesized by the
body itself, and can only be sourced from
outside.
 Types of Vitamins

Fat Soluble Vitamins

• Soluble in lipids i.e. in fats & are insoluble in water.

• Their absorption into the bloodstream happens in the intestines.

• They are stored in human bodies as adipose tissues in the liver.

• The fat-soluble vitamins are Vitamin A, D, E and K.

Water soluble Vitamins

• These are readily dissolvable in water.

• Excess water-soluble vitamin in your body passes out through urine.

• Since they are excreted so easily they also need to be replaced regularly.

• These vitamins must be supplied to our bodies with regular diets.

• Water Soluble Vitamins are Vitamin B and Vitamin C.

 Functions of Vitamins
• Vitamins are essential nutrients for our body because they perform hundreds of
functions.

• Right from promoting growth to absorption of calcium and blood clotting, they are
everywhere.

• They are also responsible for providing cofactors or coenzymes to aminoacids for
them to carry out their catalyzing functions
 Sources & Functions Of Vitamins
• Vitamin A:
• Found in potato, carrots, pumpkins, spinach, beef and eggs.
• Required to enable night vision in humans. Cells need for
transfusion of light require Vitamin A
• Vitamin D:
• Found in fortified milk and other dairy products.
• Formation of RNA needs Vitamin D. Also helps bones absorb
calcium to stay healthy and strong and reduce the risk of fractures
• Vitamin E:

• Found in fortified cereals, leafy green vegetables, seeds, and nuts.

• Has antioxidant properties that help our bodies get rid of free radicals and assists in
formation of red blood cells

• Vitamin K:

• Found in dark green leafy vegetables and in turnip or beet green.

• Essential in creating some important proteins.

Vitamin B1 or Thiamine:
• Found in pork chops, ham, enriched grains and seeds.
• Part of an enzyme needed for energy metabolism; important for nerve function.

Vitamin B2 or Riboflavin:
• Found in whole grains, enriched grains and dairy products.
• Part of an enzyme needed for energy metabolism; important for normal vision and skin
health.
Vitamin B3 or Niacin:

• Found in mushrooms, fish, poultry, and whole grains.

• Part of an enzyme needed for energy metabolism; important for nervous system,
digestive system, and skin health.

Vitamin B5 or Pantothenic Acid:

• Found in chicken, broccoli, legumes and whole grains.

• Part of an enzyme needed for energy metabolism.

Vitamin B6 or Pyridoxine:

• Found in fortified cereals and soy products.

• Part of an enzyme needed for protein metabolism; helps make red blood cells.

Vitamin B7 or Biotin:

• Found in many fruits like fruits and meats.

• Part of an enzyme needed for energy metabolism.

Vitamin B9 or Folic Acid:

• Found in leafy vegetables.

• Part of an enzyme needed for making DNA and new cells, especially red blood cells.

Vitamin B12(Cobalamin):

• Found in fish, poultry, meat and dairy products.

• Part of an enzyme needed for making new cells; important for nerve function.
• Vitamin C(Ascorbic acid):

• Found in citrus fruits and juices, such as oranges and grapefruits.

• Antioxidant, part of an enzyme needed for protein metabolism; important for immune
system health; aids in iron absorption.
 Deficiencies of Vitamins
1. Vitamin A – Hardening of the cornea in the eye, night blindness.
2. Vitamin B1 – Deficiency may cause beriberi and dwarfism.
3. Vitamin B2 – Deficiency can cause disorders in the digestive system, skin burning sensations, and cheilosis.
4. Vitamin B6 – Deficiency of B6 causes convulsions, conjunctivitis, and sometimes neurological disorders.
5. Vitamin B12 – Its deficiency can cause pernicious anaemia and a decrease in red blood cells in haemoglobin.
6. Vitamin C – It is a water-soluble vitamin, its deficiency causes bleeding in gums and scurvy.
7. Vitamin D – It is obtained by our body when exposed to sunlight. Its deficiency causes improper growth of bones,
soft bones in kids, and rickets.
8. Vitamin E – Deficiency of vitamin E leads to weakness in muscles and increases the fragility of red blood cells.
9. Vitamin K – It plays an important role in blood clotting. The deficiency of vitamin K increases the time taken by
the blood to clot. Severe deficiency may cause death due to excessive blood loss in case of a cut or an injury.
 HORMONES
• Hormones are the chemical
messenger produced in small amount
by endocrine glands, secreted into
blood stream to control metabolism
and biological activities in target cell
or organs.
 Characteristics or properties of hormone:
▪ Low molecular weight

▪ Small soluble organic molecules

▪ Rate of diffusion is very high and are readily oxidized but the effect does not remains constant

▪ It is effective in low concentration

▪ Travels in blood

▪ It has its target site different from where it is produce and is specific to a particular target

▪ Hormones are non-specific for organisms and may influences body process of other individuals
 Functions of hormones

▪ Regulatory and homeostasis functions

▪ Maintain consistency of interior of cell

▪ Permissive functions; movement of substance in and out of cell

▪ Integrative function; usually balance two system

▪ Developmental function; helps in development of foetus

Classification of hormone

• Hormones are classified

• On the basis of chemical nature
• On the basis of mechanism of hormone action
• Group I hormone
• Group II hormone
A. On the basis of chemical nature:

• Protein hormones: insulin, glucagon

• Steroid hormone: sex hormones, glucocorticoids
• Aminoacids derivatives hormones: epinephrine, nor epinephrine
etc
On the basis of mechanism of hormone action

1. Group I hormone (lipophilic hormone):

▪ These hormones are lipophilic in nature.
▪ They are mostly derivatives of cholesterol.
▪ These hormones binds to intracellular receptors
▪ Example: Steroid hormones, Estrogen, androgen, glucocorticoids, cholcalciferol, thyroxine etc

2. Group II hormones (water soluble hormone):

▪ These hormones binds to cell surface receptors and stimulates the release of certain molecules
(secondary messengers) to perform biochemical functions
On the basis of secondary messengers group II hormones are of 3 types;

i. Secondary messenger is cAMP:

▪ eg. Adrenocorticotropic hormone, FSH, LH, PTH,ADH, calcitonin, glucagon,

ii. Secondary messenger is phosphotidylinocitol/calcium or both:

▪ eg. Acetylcholine, vasopressin, cholecystokinin, gastrin, gonadotropin releasing hormone, thyrotropin
releasing hormone,
▪ Insulin, chorynoic somato mamotropin, epidermal growth factors, fibroblast growth factors, GH, prolactin

iii. Secondary messenger is cGMP:

▪ Atrial natriuretic peptide (ANP)
Hormones Released by Endocrine system
• Refers to tissue that makes and release hormones that travel in the blood stream
and control the actions of other cells or organs.

• The endocrine system is a complex network of glands and organs. It uses

hormones to control and coordinate your body's metabolism, energy level,
reproduction, growth and development, and response to injury, stress, and mood.
Endocrine system consists of the following glands:
• Hypothalamus.
• Pituitary gland
• Pineal gland.
• Thyroid.
• Parathyroid glands.
• Adrenal glands.
• Pancreas.
• Ovaries.
• Testes.
Other body tissues that release hormones include:
• Adipose tissue(fat tissue).
• Kidneys.
• Liver.
• Gut (gastrointestinal tract).
• Placenta.
Hypothalamus
• It is a small region of your brain that connects to pituitary
gland through the pituitary stalk.

• It releases several hormones that control pituitary gland.

• Corticotrophin-releasing hormone.

• Dopamine

• Gonadotrophin-releasing hormone.

• Growth hormone-releasing hormone.

• Oxytoxcin ( hypothalamus makes oxytocin, but your

pituitary gland stores and releases it).

• Somatostatin

• Thyrotropin-releasing hormone.
• Pituitary gland
• It is a pea-sized gland at the base of brain, behind the bridge of nose and directly below hypothalamus.

• The anterior pituitary makes and releases the following six hormones:

• Adrenocorticotropic hormone(ACTH or corticotropin)

• Follicle- stimulating hormone(FSH)

• Growth hormone (GH).

• Luteinizing hormone(LH).

• Prolactin.

• Thyroid-stimulating hormone (TSH).

• The posterior pituitary releases the following hormones:

• Antidiuretic hormone (ADH, or vasopressin).

• Oxytocin.
• Pineal gland
• It is a tiny gland in brain that’s located beneath the back
part of the corpus callosum (nerve fibers that connect
the two parts of your brain).

• It releases the hormone melatonin, which helps control

your sleep-wake cycle.
• Thyroid gland
• It is a small, butterfly-shaped gland located at the front of
your neck under skin.
• Thyroid’s main job is to control the speed of your
metabolism (metabolic rate), which is the process of how
your body transforms the food consume into energy.
• Your thyroid releases the following hormones:
• Thyroxine (T4).
• Triiodothyronine (T3).
• Reverse triiodothyronine (RT3).
• Calcitonin.
• Thyroxine and triiodothyronine are often collectively
called “thyroid hormone”.
• Parathyroid glands

• Have four pea-sized parathyroid glands located

behind their thyroid gland (the butterfly-shaped
gland in your neck).

• Sometimes, parathyroid glands are located along

your esophagus or in chest.

• These are known as ectopic (in an abnormal place)

parathyroid glands.

• The main job of your parathyroid glands is to

release Parathyroid hormone(PTH), which is
responsible for the calcium balance in your blood
and bone health.
• Adrenal glands
• These also known as suprarenal glands, are
small, triangle-shaped glands that are located
on top of each of two kidneys.
• Adrenal glands make the following
hormones:
1. Cortisol
2. Aldosterone.
3. DHEA and androgens.
4. Adrenaline (epinephrine).
5. Noradrenaline (norepinephrine).
• Pancreas

• Your pancreas is an organ in the back of

abdomen (belly). It’s part of digestive
system and endocrine system.

• The islet cells (endocrine cells) in pancreas

make the following hormones:

• Insulin.

• Glucagon.
Ovaries
• Have two ovaries — each located on both sides of their uterus below the opening of
the fallopian tubes.

• In addition to containing the egg cells necessary for reproduction, the ovaries produce
the following hormones:

• Estrogen.

• Progesterone.

• Testosterone.
• Testes
The testes are part of the male reproductive system and produce the hormone testosterone.
Adipose tissue (fat tissue)
• It’s located all over your body, including under your skin, around internal organs, between
muscles, in bone marrow and breast tissue.
• Adipose tissue makes and releases the following hormones:
• Leptin.
• Adiponectin.
• Plasminogen activator inhibitor-1.
• Estrogen.
• Angiotensin.
• Kidneys
• Thsese are two bean-shaped organs that filter your blood.

• They’re part of urinary system, but they also produce hormones, including:

1. Erythropoietin.

2. Renin.

• Liver
• Liver is an essential organ and gland, performing hundreds of functions necessary to sustain life. It’s
considered part of your digestive system, but also produces hormones, including:

1. Insulin-like growth factor 1 (IGF-1).

2. Angiotensinogen.
Gut (gastrointestinal tract)
• It is the long, connected tube that starts at your mouth and ends at intenstine.

• It’s responsible for digestion. Scientists are currently studying the hormones that gut makes and
their effects. These hormones include:

1. Ghrelin.

2. Somatostatin.

3. Glucagon-like peptide 1 (GLP-1).

Placenta
• The placenta is a temporary organ that develops in uterus during Pregnancy.
• It provides oxygen and nutrients to the developing fetus.
• The placenta produces the hormones estrogen and progesterone to maintain the pregnancy