Biomolecules

 Biomolecules are the compounds needed for life.
 Biomolecules are the molecules present in a living
organism.
 These biomolecules are fundamental building blocks of
living organisms as they support the biological processes
essential for life. E.g. carbohydrates, proteins, nucleic
acids, lipids, vitamins, etc.
 The principle organic constituents in a living cell are
as following:

1. Most of them are organic compounds.
2. Functional group determines their chemical
properties.
3. Most biomolecules are asymmetric.
4. Building block molecules have simple structure.
5. Biomolecules first grow by chemical evolution.

 These are the compounds of carbon, hydrogen and oxygen.
On hydrolysis, they yield simple sugar.
 Sugars are aldehyde or ketone derivatives of polyhydric
alcohols i.e.
 Glycerol (-OH = alcohol group)
 Glyceric aldehyde (-CHO = aldehyde group),
 Dihydroxyl acetone (-CO = ketone group)

 Monosaccharides, disaccharides and polysaccharides are all
carbohydrates, but the most important carbohydrate in
nature is dextrose (glucose).
 All carbohydrates are converted in to it before oxidation in
tissues.

 These are the neutral fats, oils and waxes and just like
carbohydrates lipids are compounds of carbon, hydrogen
and oxygen.
 They occur in plant and animal tissues and are insoluble in
water, but are soluble in organic solvents like chloroform,
benzene, ether, alcohol, etc.

 These are complex nitrogenous compounds of carbon,
hydrogen, oxygen and nitrogen.
 Sometimes they may also contain other elements like
sulphur, phosphorus, iron, etc.
 They have high molecular weight and on hydrolysis i.e. on
decomposition of reaction with water, they form amino
acids.

 An amino acid, is an organic compound which contains
amino (NH2) group and a carboxyl (-COOH) group.
 Glycerine is the simplest amino acid.
 20 different amino acids have been isolated from different
proteins.

 These are the largest and the most fascinating molecules
found in living matter.
 These are the carriers and mediators of genetic information
from one generation to another and exert primary control
over basic life processes in all organisms.
 Like proteins, nucleic acids are also polymers.

 Carbohydrate are defined as polyhydroxyalcohols with
aldehydes and ketones and their derivatives.
 These are widely distributed both in animal and plant
tissues.
 In animals, carbohydrates in the form of glucose and
glycogen serve as an important source of energy.
 Some carbohydrates have highly specific functions; E.g.
ribose and deoxyribose are carbohydrates which are
components of nucleoproteins.

Carbohydrate are divided into four major types:
Monosaccharide's:
 These are often called as simple sugars.
 Which cannot be hydrolysed into a simpler form.
 The general formula is Cn(H2O)n.
 They can be further sub-divided as shown in above
table.

Sr. No. Carbon atoms
(No)
Aldoses : Examples Ketoses : Examples
1. Trioses (3) Glyceraldehydes or glycerose Dihydroxyacetone
2. Tetroses (4) Erythrose Erythrulose
3. Pentoses (5) Ribose, xylose, arabinose Ribulose, xylulose
4. Hexoses (6) Glucose, galactose, mannose Fructose
5. Heptoses (7) Glucoheptose, galactoheptose Sedoheptulose

Disaccharides:
 These carbohydrates produce two molecules of the same or
different monosaccharide's on hydrolysis.
 The general formula is Cn(H2O)n – 1.
 Examples: Lactose, Maltose, Sucrose.
Oligosaccharides: These carbohydrate yield 2-10
monosaccharide unit on hydrolysis, E.g. Maltotriose.

Polysaccharides:
 These carbohydrates yield more than ten molecules of
monosaccharide’s on hydrolysis.
 The general formula is (C6H10O5)n.
 Sub-class:
 Homo-polysaccharide’s : Starch, glycogen, cellulose,
dextrin.
 Hetero-polysaccharide’s: Mucopolysaccharides.

 A carbon atom to which four different atoms or groups of
atoms are attached is said to be asymmetric carbon atom.
 Many biochemical's contain two or more asymmetric
carbon atoms.
 The presence of asymmetric carbon atom allows formation
of isomers.
 The compounds which have the same structural formula, but
differ only in spatial configuration are called as stereo – isomers
or geometric isomers.

 Isomers of carbohydrates are classified as
under:
 D and L isomer:
 The designation of an isomer as D- or L- form is
determined by spatial configuration to the
parent compound.
 When –OH group around the carbon atom at
right side, the sugar belongs to D-series.
 If the –OH group is on left side, it is a member
of L-series.

 Optical isomer:
 When a beam of polarised light passed through a solution
exhibiting optical activity, it will be rotated to right or left
in accordance with presence of optical isomer.
 A compound which causes rotation of polarised light to the
right is said to be dextro-rotatory and is designated with
plus (+) sign.
 Rotation of beam to the left is termed as leavo-rotatory and
is designated with minus (-) sign.

 Epimer:
 Isomers formed as a result of interchange of –OH and –H on
carbon atoms 2, 3 and 4 of glucose are known as epimers.
 In the body, epimerisation take place by the enzyme epimerase.
 Biologically, most important epimers of glucose are mannose and
galactose formed by epimerisation at carbon 2 and 4 respectively.

 Anomer (α and β):
 The cyclic structure of glucose is retained in solution, but isomerism takes
place about position 1.
 This is accomplished by optical rotation (mutarotation) by which the
position of –H and –OH groups are changed around carbon 1.
 Inter-conversion of α and β glucose in solution with change of optical
activity is called mutarotation.

 Pyranose and Furanose:
 All sugars forming six membered rings are called as pyranoses and those
forming five membered rings are called as furanoses.
 Amylene oxide form of glucose = glucopyranose.
 Butylene oxide form of glucose = glucofuranose.

 Aldose and Ketose:
 Fructose has same molecular formula as that of glucose but
differs in its structural formula since carbon-2 is a part of CO
group, which make fructose a ketose sugar rather than aldose.
Structure of β-D-Fructose

MONOSACCHARIDE'S:
Sr.
No.
Sugar Source Physiological importance
1. D-Ribose Nucleic acid Structural elements of nucleic acids and
coenzymes, e.g. ATP, NAD, NADOP, FAD.
2. D-Ribulose In metabolic
processes
Intermediates in hexosemonophosphate
shunt.
3. D-
Arabinose
Plum and cherry
gums
Bacterial metabolism
4. D-Xylose Wood gums Bacterial metabolism
5. D-Lyxose Heart muscle Component of lyxoflavin isolated from
human heart muscle.
Physiological importance of some Pentose

MONOSACCHARIDE'S:
Sr.
No.
Sugar Source Physiological importance
1. D-Glucose Fruit juice, cane sugar,
maltose, lactose, etc.
Carried by blood and used by
tissues.
Presence in urine is called glycosuria.
2. D-Fructose Fruit juice, honey.
Hydrolysis of cane
sugar.
Changed to glucose in liver and
intestine and thus used in body.
3. D-Galactose Hydrolysis of lactose. Changed to glucose in liver and
metabolised.
4. D-Mannose Hydrolysis of plant
mannosans and gums
Constituents of prosthetic
polysccharides of albumins,
globulins, mucoproteins.
Physiological importance of some Hexoses

MONOSACCHARIDE'S:
Glycosides:
 These are the compounds formed by consideration between
a sugar and the hydroxyl group of second compound called
aglycone which may or may not be another sugar.
 Physiological importance:
 Glycosides are found in many drugs, spices and animal
tissues.
 Cardiac glycosides, e.g. digitalis contain steroids as aglycone.
 Other glycosides include antibiotics like streptomycin.

MONOSACCHARIDE'S:
Amino sugar (Hexosamines):
 Sugar containing amino group are called as amino sugar; e.g.
D-galactosamine, D-glucosamine, D-mannosamine.
 Physiological importance:
 Glucosamine is a component of hyaluronic acid.
 Galactosamine is a consituents of glycoproteins.
 Mannosamine is an important constituent of mucoprotein.
 Several antibiotics like erythromycin, carbomycin contain
amino sugars.

DISACCHARIDE'S: Physiological importance
 Maltose (Malt sugar): It does not occur in the body. It is
present in germinating cereals and malt. It is the intermediate
product in the breakdown of starch by amylase in the alimentary
tract.
 Lactose (Milk sugar): It is present in milk and formed in
lactating mammary glands. It may occur in urine during
pregnancy.
 Sucrose (Cane sugar): It occurs in cane sugar, pineapple, carrot
roots, sweet potato and honey. It is hydrolysed to glucose and
fructose by sucrase in the alimentary canal and product are
absorbed.

POLYSACCHARIDE'S: Physiological importance
 Cellulose: It is the main constituents of supporting tissues of
plants and forms a considerable part of vegetable food. It does not
occurs in animal. It is not acted upon by amylase in digestive
system.
 Glycogen (Animal starch): It is the reserved carbohydrate
found in liver and muscle of animals and human beings. The
glycogen content of liver is more than that of muscle. It is also
found in plants which have no chlorophyll system; e.g. fungi and
yeast. Not present in green plants.

POLYSACCHARIDE'S: Physiological importance
Starch: It is the store of carbohydrate in green plants. Most
important source of carbohydrate in our food and found in
potatoes, legumes, and other vegetable in high
concentrations. It is a mixture of two substances: amylase
and amylopectin.
Dextrin's: Dextrin’s are formed by partial hydrolysis of
starch by an enzyme, salivary amylase, dilute mineral acids or
heats. Have faint sweet taste.

B. LIPIDS:
 The lipids are heterogenous compounds related to fatty
acids.
 They are insoluble in water and soluble in organic solvents
like ether, chloroform and benzene.
 Chemically they are esters of fatty acids and alcohols.

Biological Significance of Lipids:
 Lipids (fats) serves as an efficient source of energy. They are stored
in adipose tissue.
 The fat-soluble vitamins and essential fatty acids are found with
the fat of natural food.
 Serve as an insulating material in the sub-cutaneous tissues and
around certain organs.
 Lipoproteins (combinations of fat and protein) and glycolipids
(combinations of fat and carbohydrate) are essential for
maintaining cellular integrity.
 Provide building blocks for different high molecular weight
substance, e.g. acetic acid can be used for synthesis of cholesterol.

1. Simple Lipids:
 Simple lipids are further sub-classified as fat and
waxes.
(i) Fats:
 They are esters of fatty acids with glycerol.
 They are the best reserves of food material in human
body.
 Acts as insulator for the loss of body heat.
 Acts as padding material for protecting internal organs.
 The chemical structure of fat consists of three different
molecules of fatty acids (R1, R2, R3) esterified with three
hydroxyl groups of glycerol.

1. Simple Lipids:
(i) Fats:
Structure of Fats (Triglycerides)

1. Simple Lipids:
(i) Fats: Fats are characterised by following parameters:
 Saponification number: It is defined as the number of
mgs of KOH required to saponify 1 gm of fat or oil. It is
depends on number of –COOH groups present on the
fat/oil. Fat containing short chain fatty acids will have
more –COOH groups and will have higher saponification
number.
 Acid number: Defined as number of mgs of KOH
required to neutralise free fatty acids of 1 gm of fat. The
acid number indicates degree of rancidity of the given fat.

1. Simple Lipids:
 Iodine number: It is the amount (in gms) of iodine
absorbed by 100 gm of fat. It is the measure of degree of
unsaturation of fat. Highly unsaturated fatty acids will
have higher iodine number.
 Acetyl number: It is the number of mgs of KOH
required to neutralise the acetic acid obtained by
saponification of 1 gm of fat after it has been acetylated.

1. Simple Lipids:
 Polenske number: It is the number of ml of 0.1 N KOH
required to neutralise the insoluble fatty acids from 5 gm
of fat.
 Wollny number: It is the same as Polenske number
except that the soluble fatty acids are measured by
titration of the distillate obtained by steam distillation of
the saponification mixture. It indicates how much
volatile fatty acid can be extracted from fat through
saponification.

1. Simple Lipids:
(ii) Waxes: Waxes are esters of fatty acids with higher
alcohols other than glycerol. In human body, commonest
waxes are esters of cholesterol. They are of three:
 True waxes are esters of higher fatty acids with acetyl
alcohol or other higher straight chain alcohols.
 Cholesterol esters are esters of fatty acid with cholesterol.
 Vitamin A and vitamin D are palmitic/ stearic acid esters
of vitamin A (Retinol) or vitamin D respectively.

2. Compound Lipids:
 They are esters of fatty acids containing groups in
addition to an alcohol and a fatty acid. They are
further sub-classified as:
(i) Phospholipids (phosphatides):
 They are esters of fatty acids with glycerol containing
as esterified phosphoric acid and a nitrogen base.
 They are present in large quantity in nerve tissue,
brain, liver, kidney, pancreas and heart.

2. Compound Lipids:
 Biological importance:
 They increase the rate of fatty acid oxidation.
 They act as carriers of inorganic ions across the
membrane.
 They help in blood clotting.
 They act as prosthetic group to certain enzymes.
 They form the structures of membranes, matrix of cell
wall, myelin sheath, microsomes and mitochondria.

2. Compound Lipids:
 Phospholipids are further sub-classified as:
(a) Glycerophosphatides: In this type of
phospholipids, glycerol is the alcohol group.
Example: Phosphatidic acid, Lecethin, Cephalin.

2. Compound Lipids:
(b) Phosphoinositides: In this type, inositol is the
alcohol.
Example: Phosphatidyl inositol (Lipositol).

2. Compound Lipids:
(c) Phosphosphingosides: In this type, sphingosine is
an amino alcohol.
Example: Sphingomyelin.

2. Compound Lipids:
 Clinical importance of phospholipids:
 In Niemann-Pick disease, excess amount of
sphingomyelin are deposited in brain, liver and spleen.
 It is due to deficiency of enzyme sphingomyelinase.
 The symptoms are: enlarged liver and spleen, mental
retardation, anaemia and leucocytosis.

2. Compound Lipids:
(ii) Glycolipids: These lipids contain amino alcohol
(sphingosine or iso-shingoshine) attached with an
amide linkage to a fatty acid and glycosidically to a
carbohydrate group (sugars, amino acid, sialic acid),
they are further sub-classified as follows:
(a) Cerebrosides
(b) Gangliosides
(c) Sulpholipids
(d) Amino lipids

2. Compound Lipids:
(ii) Glycolipids: Sub-classified as follows:
(a) Cerebrosides: They contain galactose, a high molecular
weight fatty and sphingosine. They are chief constituent of
myelin sheath. Cerebrosides are in much higher concentration
in medullated rather than in non-medullated nerve fibres. E.g.
Kerasin, Cerebron.
 Clinical importance: In Gaucher’s disease, cerebroside
content of reticuloendothelial cell (spleen) is very high. It is
caused by deficiency of enzyme glucocerebrosidase.
 Symptoms: Increase in size of spleen, leucopenia, liver
enlargement.

2. Compound Lipids:
(b) Gangliosides: They are glycolipids occuring in the brain.
They contain ceramide (sphingosine + fatty acid), glucose,
galactose and sialic acid. There are three types of gangliosides:
GM1, GM2 and GM3.
 GM1 is due to deficiency of enzyme β-galactosidase.
 GM2 termed as Tay Sach’s disease, caused due to deficiency of
enzyme hexosaminidase.
 Symptoms: mental retardation, blindness and muscular
weakness.

2. Compound Lipids:
(b) Sulpholipids (sulphatides): These have been isolated
from brain and other animal tissues. These are sulphate
derivatives of the galactosyl reduce in cerebrosides.
(c) Amino lipids: Phosphatidyl ethanoamine and serines
are amino lipids and sphingomyelins, gangliosides contain
substituted amino groups.

2. Compound Lipids:
(b) Sulpholipids (sulphatides): These have been isolated
from brain and other animal tissues. These are sulphate
derivatives of the galactosyl reduce in cerebrosides.
(c) Amino lipids: Phosphatidyl ethanoamine and serines
are amino lipids and sphingomyelins, gamgliosides
contain substituted amino groups.

2. Compound Lipids:
(iii) Lipoproteins: Characteristics:
 To form a hydrophilic lipoprotein complex, there should be a
combination of triacylglycerol (45%), phospholipids (35%),
cholesterol and cholesteryl esters (15%), free fatty acids (<5%)
and protein.
 The density of lipoprotein increases as the protein content rises
and the lipid content falls and the size of the particle becomes
smaller.
 Four major group of lipoproteins have been identified. They are
physiologically important. They used in clinical diagnosis is
some metabolic disorders of fat metabolism.

2. Compound Lipids:
(iii) Lipoproteins: Four sub-types are as follows:
(a) Chylomicrons: Both chylomicrons and VLDL contain
triacyl glycerol (50%) and cholesterol (23%) as
predominant lipids. Their concentration is increased in
atherosclerosis and coronary thrombosis.
(b) Very low density lipoproteins (VLDL/pre-β-
lipoproteins): It is assembled in the liver from
triglycerides, cholesterol and apolipoproteins.

2. Compound Lipids:
(iii) Lipoproteins: Four sub-types are as follows:
(c) Low density lipoproteins (LDL/ β-lipoproteins):
Predominant lipid in LDL is cholesterol (46%) and
phospholipids (23%). It is increased in
atherosclerosis, coronary thrombosis.
(d) High density lipoproteins (HDL/ α-lipoproteins):
Predominant lipid in HDL is phospholipid (27%) and
proteins (>45%)

2. Compound Lipids:
(iii) Lipoproteins: Physiological Importance:
 To transport and deliver the lipids to tissues.
 To maintain structural integrity of cell surface and
sub-cellular particles like mitochondria and
microsomes.
 The β-lipoproteins fraction increases in severe
diabetes mellitus and atherosclerosis.

3. Derived Lipids:
 They are classified in to two categories: fatty acid and
steroids.
(i) Fatty acids:
 These are obtained by hydrolysis of fats.
 Fatty acids occuring in natural fats usually contain an even
number of carbon atoms. Usually they are straight chain
derivatives.
 The straight chain may be either saturated or unsaturated.
In addition, there are few fatty acids which are typical.

3. Derived Lipids:
a) Saturated Fatty acids: General formula for saturated
fatty acid is CnH2n+1COOH.
Sr. No. Name of acid Formula Number of
carbon atoms
1. Acetic CH3COOH 2
2. Propionic C2H5COOH 3
3. Butyric C3H7COOH 4
4. Capronic C5H11COOH 6
5. Caprylic C7H15COOH 8
6. Decanoic (Capric) C9H19COOH 10
7. Lauric C11H23COOH 12
8. Myristic C13H27COOH 14
9. Palmitic C15H31COOH 16
10. Stearic C17H35COOH 18
11. Arachidic C19H39COOH 20
12. Behenic C21H43COOH 22
13. Lignoceric C23H47COOH 24

3. Derived Lipids:
b) Unsaturated fatty acids: Unsaturated fatty acids are
classified as mono-unsaturated fatty acid (MUFA) and poly-
unsaturated fatty acid (PUFA).
Sr. No. Type of acid Name of acid Formula Number of
carbon
atoms
1. Mono-unsaturated Palmitoleic C15H29COOH 1
2. Mono-unsaturated Oleic C17H33COOH 1
3. Poly-unsaturated Linoleic C17H31COOH 2
4. Poly-unsaturated Linolenic C17H29COOH 3
5. Poly-unsaturated Arachidonic C19H31COOH 4
Eicosanoids
6. Protanoids Timmoionic C19H33COOH 5
7. Leukotrienes Clupanodonic C12H32COOH 5
8. Leukotrienes Cervonic C21H31COOH 6

3. Derived Lipids:
b) Unsaturated fatty acids:
 Prostanoids (PUFA) are subclass of eicosanoids which are
further sub-divided as Prostaglandins (PG) and
Thromboxanes (TX) and Prostacyclins (PGI2)
 General characteristics of prostanoids are as follows:
 All are having 20 carbon compounds.
 Trans double bond is at 13 position.
 -OH group is at 15 position.

3. Derived Lipids:
 Classification of Prostanoid and Leukotriene.

3. Derived Lipids:
 Prostaglandins (PG):
 They exist in almost every mammalian tissue and act as local
hormones.
 They have important physiological and pharmacological
activities.
 They are obtained from arachidonic acid to form a
cyclopentane ring.
 PGE2

3. Derived Lipids:
 Thromboxanes (TX):
 They contract smooth muscles on blood vessels, GI tract, uterus
and bronchioles.
 They are located in platelets, and have the cyclopentane ring
interupted with an oxygen atom (oxygen ring).
 TXA2

3. Derived Lipids:
 Leukotrienes:
 They are third group of eicosanoid derivatives formed by the
lipooxygenase pathway.
 They are located in leucocytes and are characterised by the
presence of three conjugated double bonds. Forth double bond
in LTA4 is not conjugated.
 LTA4

3. Derived Lipids:
 Essential Fatty Acids:
 Fatty acids which are essential for growth and health of
humans and other animals have been termed as essential
fatty acids.
 They are poly-unsaturated fatty acids which are not
synthesized in the body, but are taken form natural
sources.
 Examples: Linoleic acid, Linolenic acid, arachidonic acid.
 They have low melting points and iodine number.

3. Derived Lipids:
 Essential Fatty Acids:
 Physiological importance of essential fatty acids:
1. They are structural constituents of the cell.
2. They cause prolongation of clotting and increase hydrolytic
activity.
3. They cure skin lesions.
4. Their deficiency in diet of babies causes eczema.

3. Derived Lipids:
(ii) Steroids:
 Steroids are often found in association with fat.
 They have a cyclic nucleus resembling phenanthrene (ring A,B,C) to
which a cyclopentane ring (D) is attached.
 The structure and nomeclature for numbering of carbon atoms is shown
in Fig.
 Methyl side chains occurs at positions 10 and 13.
 A side chain at position 17 is usual.
 If the compound has one or more hydroxyl groups and no carbonyl or
carboxyl groups, is called as sterol.

3. Derived Lipids:
(ii) Steroids:
 Steroids are divided in following manner:
 Sterols: Cholesterol, ergosterol, coprosterol.
 Bile acids: Glycocholic acid, taurocholic acid.
 Sex hormones: Testosterone, estradiol.
 Vitamin D: Vitamin D2 and D3.
 Adrenocortico hormone: Corticosterone, hydroxyl corticosterone.
 Cardiac glycosides: Stropanthin.
 Saponins: Digitonin, digitoxin.

C. Nucleic Acids:
 Nucleic acids are made up of nucleotides.
 Nucleotides are composed of purine or pyrimidine bases,
ribose or deoxyribose sugars and phosphoric acid.
 When phosphoric acid from a nucleotide is removed, the
remainder part is termed as nucleoside.
 Thus a nucleoside is composed of a purine or pyrimidine
base and a ribose or a deoxyribose sugar.

C. Nucleic Acids:
 The nomenclature indicating numbers to carbon/nitrogen
atoms of purine and pyrimidine are indicated below:
Structure and nomenclature of Purine and Pyrimidine

C. Nucleic Acids:
 Biological importance of Nucleotides:
 Nucleotides are important intracellular molecules of low molecular
weight.
 They play an important role in carbohydrate, fat and protein
metabolism.
 The most important role of nucleotides is of being precursors of DNA
and RNA.
 The purine nucleotides also act as the high energy source ATP, cAMP
in a wide variety of tissues and organisms.
 The pyrimidine nucleotides also act as high energy intermediates such
as UDP-glucose and UDP-galactose in carbohydrate metabolism.

D. Amino Acid and Proteins:
 Proteins are made up of amino acids.
 An intermediate stage between amino acids and proteins is of
peptides.
 Hence some basic information on amino acids and peptides is
essential.
 Although there are 200 amino acids found in nature, only 20 of them
occur in proteins.
 The general structure of an amino acid is

D. Amino Acid:
 Common Properties of Amino Acids:
 Amino acids have at least two ionisable groups i.e. –COOH and –
NH3+. Carboxyl group dissociates more easily than amino group. In
solution, two forms of these group, one charged and one neutral, exist
in protonic equilibrium with each other.
R-COOH R-COO- + H+ and R-NH3+ H+ + R-NH2
 R-COOH and R-NH3+ represent the protonated or acid partners in
these equilibria. R-COO- and R-NH2 are conjugated bases (i.e. proton
acceptors) of the corresponding acids.
 Normal pH of blood is 7.4 at this pH carboxyl groups exist almost
entirely as the conjugated base i.e. R-COO-.

D. Amino Acid:
 Structure of Amino Acids:
 Based on the structure of amino acids in proteins, they are classified into seven
classes as follows:
 Their examples are also cited along with type of class.
 With aliphatic side chains: Glycine, alanine, valine, leucine and isoleucine.
 With side chains containing hydroxyl (-OH) groups: Serine, threonine.
 With side chains containing sulphur atoms: Cysteine, methionine.
 With side chains containing acidic groups: Aspartic acid, glutamic acid.
 With side chains containing basic groups: Arginine, lysine, hydroxyl lysine,
histidine.
 With side chains containing aromatic rings: Phenyl alanine, tyrosine,
tryptophan.
 Imino acids: Proline, hydroxyproline.

D. Amino Acid:
 Glutathione:
 It is a tripeptide consisting of glutamic acid, cysteine and glycine.
 It is converted to disulphide form by dehydrogenation and is
involved in oxidation-reduction reaction.
 It is required for action of several enzymes and that of insulin.
 Oxytocin and vasopressin:
 These are cyclic peptide hormones consisting of 8 amino acids
and located in pituitary gland.
 Oxytocin functions on uterine muscle and aids in ejection of
milk.

D. Amino Acid:
 Carnocin:
 It is a dipeptide consisting of β-alanine and histidine.
 It is a dipeptide of voluntary muscle.
 Bradykinin:
 It is a monopeptide consisting of 9 amino acids.
 It is most potent pain- producing substance.
 It mediates production of PGE2 from arterial walls.

D. Amino Acid:
 Angiotensin:
 Agniotensin I consists of 10 amino acids and has slight effect on blood
pressure.
 Angitoensin I is further converted to Angiotensin II by splitting two
amino acid.
 Angiotensin II has prominent effect on blood pressure. It stimulate
thirst, causes dilation of blood vessels of voluntary muscles and brain.
 Antibiotics:
 Biologically active antibiotics are obtained from fungi and contain both
D- and L- amino acids and amino acids absent in protein.

D. Proteins:
 Proteins are define as high molecular weight mixed
polymers of α-amino acids joined together with peptide
linkage (-CO-NH-).
 Proteins are chief constituents of all living matter.
 They contain carbon, hydrogen, nitrogen, sulphur and
phosphorus.

D. Proteins:
 Biological significance of proteins:
 Protein are essence of life processes.
 They are fundamental constituents of all protoplasm and
are involved in structure and functions of living cells.
 Enzymes are made up of proteins.
 The cementing substances and the reticulum which binds
or holds the cell as tissues or organs is made up of proteins.
 Homeostatic control of volume circulating blood and of
interstitial fluids is through plasma proteins.

D. Proteins:
 Biological significance of proteins:
 Proteins are involved in blood clotting through thrombin,
fibrinogen and through other protein factors.
 Antibodies, which are defending factors against infections
are proteinous in nature.
 Nucleoproteins in the cell nucleus perform hereditary
transmission.

D. Classification of Proteins:

1. Simple Proteins:
Sr. No. Class of protein Characteristics Examples
1. Albumins
Soluble in water, precipitated at
high salt conc.
Serum albumin, egg
albumin, lactalbumin (milk),
etc.
2. Globulins
Insoluble in water, soluble in
dilute salt solution.
Serum albumin, vitelin (egg
yolk), turberin (potato), etc.
3. Glutelins
Insoluble in water, soluble in
dilute acids and alkalies, mostly
found in plants.
Glutenin (wheat), oryzenin
(rice).
4. Prolamines
Insoluble in water and absolute
alcohol, soluble in 70-80%
alcohol.
Gliadin (wheat), zein (maize)
5. Protamines
Basic proteins of low molecular
weight, soluble in water, dil.
Acids and alkalies.
Salmine (salmon sperm)
6. Histones
Soluble in water, insoluble in very
dil. Ammonium hydroxide.
Globin of haemoglobin and
thymus histone.
7. Scleroprtoeins
Insoluble in water, dil. Acids and
alkalies.
Keratin (hair, horn, nail),
collagen (bone, skin), etc.

2. Conjugated Proteins:
1. Nucleoproteins
Composed of simple basic
proteins (protamine/histamines)
with nucleic acids, located in
nuclei, soluble in water.
Necleoprotamines,
Nucleohistones
2. Lipoproteins
Combination of proteins with
lipids, e.g. fatty acids,
Lipoproteins of egg – yolk,
milk, blood, etc.
3. Glycoprtoteins
Combination of proteins with
carbohydrates.
Mucin (saliva), ovomucoid
(egg white).
4. Phosphoproteins
Contain phosphorous radical as a
prosthetic group.
Caseinogens (milk), ovovitellin
(egg yolk)
5. Metalloproteins
Contain metal ions as prosthetic
group: Fe, Co, Mg, Zn, etc.
Siderophilin (Fe),
Ceruloplasmin (Cu)
6. Chromoproteins
Contain porphyrin (with iron) as
prosthetic group.
Heamoglobin, myoglobin,
catalase.
7. Flavoproteins
Contain riboflavin as their
prosthetic group.
Flavoproteins of liver and
kidney.

3. Derived Proteins:
Primary derivatives
1. Proteans
Derived in early stage of protein
hydrolysis by dil. Acids, enzymes
or alkalies.
Fibrin from fibrinogen
2. Metaproteins
Derived in later stage of protein
hydrolysis by slightly stronger
acids and alkalies.
Acid and alkali metaproteins
3. Coagulated proteins
Denatured proteins formed by
the action of heat, X-rays, ultra
violet rays.
Cooked proteins, coagulated
albumins.
Secondary derivatives
4. Proteoses
Formed by action of pepsin or
trypsin.
Albumose from albumin,
globulose from gloulin
5. Peptones
Soluble in water, not precipitated
by saturated ammonium sulphate
6. Peptide
Containing two or more amino
acids. (di-, tri-, and polypeptides)
Glycyl-alanine, leucyl-
glutamic acid.

Bonds related to Protein Structure:
 Protein structure are confirmed by two types of bonds:
1. Strong bonds:
(i) Peptide bonds:
(ii) Disulphide bonds:
2. Weak bonds:
(i) Hydrogen bonds:
(ii) Hydrophobic bonds

1. Strong bonds:
(i) Peptide bonds:
 Proteases produce polypeptide by hydrolyzing
proteins. They can also hydrolyze peptide bonds.
 Polypeptides like proteins react with biuret reagent
which is suggestive of two or more peptide bonds.

1. Strong bonds:
(ii) Disulphide bonds:
 The disulphide bond may interconnect two parallel chains
through cysteine within each polypeptide.
 The bond is not broken under usual condition of
denaturation.
Two peptide chains united by a disulphide linkage

2. Weak bonds:
(i) Hydrogen bonds:
 The hydrogen bond appears form sharing of hydrogen
atoms between the nitrogen and the carbonyl oxygen of
different peptide bonds.
 Each hydrogen bond is relatively weak.

2. Weak bonds:
(ii) Hydrophobic bonds:
 The non-polar side chains of neutral amino acids are
closely associated with one another in proteins.
 There are not true bonds.
 They play an important role in maintaining structure of
proteins.

Structure of Proteins:
 The structure of proteins is considered by several levels of
organization as mentioned below:
 Primary level of organization = Sequence of amino acids.
 Secondary level of organization = Folding of Polypeptide
chains.
 Tertiary level of organization = Relation between primary
and secondary structure.
 Quaternary level of organization = Aggregation of two and
more units.

Denaturation of Proteins:
 It is defined as the disruption of the secondary, tertiary
and quaternary structure of the native protein resulting
in alteration of the physical, chemical and biological
characteristics of protein by a variety of agents.
 The native proteins are the one which occur in animal
and plant tissues in a natural state.
 Characteristic: solubility, viscosity, optical rotation,
sedimentation rate, electrophoretic mobility, etc. during
denaturation.

Biological Significance of Denaturation:
 Precipitation of native protein as a result of denaturation
is used to advantage in the clinical laboratory.
 Blood or serum samples to be analyzed for small
molecules.
 It is used to know the enzyme-catalysed reaction of an
extract at the loss of enzyme activity when boiled and
acidified.
 A denatured protein can be renatured by appropriate
changes in the salt concentration used to precipitate the
protein.

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