2. Proteins are the most abundant and functionally
diverse molecules in living systems where they
constitute 50% or more of their dry mass.
The word protein is derived from the Greek Protos,
which means the first or supreme.
Proteins are nitrogenous macromolecules,composed
of aminoacids linked by peptide bond.

4. AMINO ACIDS
Amino acids are organic solvents.
Have two functional groups –NH₂ and
-COOH group.
The amino group is basic while carboxylic group is
acidic in nature.
Soluble in water but insoluble in organic solvents
e.g chloroform,acetone,ether,etc.
All amino acids which make up proteins are L-α-
aminoacids.
All amino acids have chiral carbon, exept Glycine.

9. LOW pH NEUTRAL HIGH pH
O O O
R C R C R C
OH O O
NH3 NH3 NH2
ammonium Form Zwitterion Carboxylate Form

10. CLASSIFICATION OF AMINO ACIDS
Although more than 300 naturally
occurring amino acids are known but only
20 amino acids take part in the formation
of all types of proteins,plants as well as
animal in origin.
These 20 amino acids are known as
Primary,Standard or normal amino acids.

11. Each of these amino acids has one or
more genetic codon(s) which are present
within the molecules of specific mRNA
which themselves are produced under
direction of genes occuring in DNA
molecules.

22. Semi-essential aminoacids.
These include Arginine and
Histidine.These are growth promoting
factors since they are not synthesized in
sufficient quantity during growth.

27. Others include
N-methyllysine,Found in myosin
Carboxyglutamate,Found in Prothrombin
Desmosine,Found in elastin

28. Non protein amino acids
These are the amino acids which donot
take part in the protein synthesis, and have
no genetic codes.They perform other
functions in human metabolism e.g

34. 6.
Citruline
Ornithine
Argininosuccinic acid
These three amino acids occur in the
liver,where they takepart in the formation
of urea.

35. 7.
Pantathenic acid.
It is a widely distributed vitamin.It forms a
part of the molecule of Co.enzymeA.
8.
Homocysteine

36. PEPTIDE BOND

37. Proteins are made by controlled polymerization of amino acids
water is eliminated
O O
two amino acids H2N CH C OH H2N CH C OH
condense to form...
R1 R2
N or amino C or carboxy
terminus O O terminus
...a dipeptide. If H2N CH C NH CH C OH + HOH
there are more it
becomes a polypeptide. R1 R2
Short polypeptide chains
are usually called peptides
while longer ones are called peptide bond is formed
proteins.
residue 1 residue 2

38. Classification of peptides
DIPEPTIDES
OLIGOPEPTIDES
Composed of 3-10 amino acids linked
together through peptide bond.e.g
Tripeptide(3 amino acids linked together
by 2 peptide bonds),Tetrapeptide(4 amino
acids linked together by 3 peptide bonds).

40. PEPTIDES
Hormones
Neuropeptides
Alkaloids
Antibiotics
Toxins
Regulatory peptides

46. 7.Bacitracin,Gramicidin
These are antibiotics.

47. UNUSUAL PEPTIDE BOND
In some cases the peptide bond in a
peptide does not involve α-COOH
group.e.g Glutathione which has the
sequence glutamic acid,cysteine and
glycine.However,the –COOH group of
glutamic acid forming peptide bond with
cysteine is not α but γ.For this reason
glutathione is chemically γ-glutamyl-
cysteinyl-glycine.

48. CLASSIFICATION OF
PROTEINS
ON THE BASIS OF MOLECULAR LENGTH
AND SHAPE.
Fibrous proteins.
When the axial ratio of length:width is more
than 10.e.g collagen,α keratin of hair.
Globular proteins.
When axial ratio of length:width of protein
molecule is less than 10.e.g
Myoglobin,haemoglobin,ribonucleases.

49. ON THE BASIS OF SOLUBILITY AND
PHYSICAL PROPERTIES.
Simple proteins
Conjugated proteins
Derived proteins

50. SIMPLE PROTEINS
These are the proteins which on complete hydrolysis yield
only amino acids.They are further classified based on
their solubilities and heat coagulabilities.
1.ALBUMIN
Soluble in water
Precipitated by full saturation with ammonium sulfate
Coagulated by heat
Examples,Ovalbumin.serum albumin,lactalbumin and
legumel

51. 2.Globulins
Insoluble in water,soluble in dilute salt
solutions.
Heat coagulable
Precipitated by half saturation with
ammonium sulfate.
Examples,serum
globulins,lactoglobulin,myosin in
muscles,ovoglobulin and legumin.

52. 3.Globins
Rich in histidine but not basic.
Combine with heme to form hemoglobin.
4.Prolamins
Soluble in ethanol,insoluble in water.
Rich in amino acid proline but deficient in
lysine.
Examples,gliadin of wheat and zein of maize.

53. 5.Protamines.
Basic proteins,soluble in NH4OH.
Rich in arginine,lack tyrosine and
tryptophan.
Form nucleoproteins with nucleic acids.
Present in sperm cells.

54. 6.Histones
Strongly basic proteins as they are rich in
arginine.
Form nucleoproteins
Soluble in water.
Lack tryptophan

55. 7.Albuminoids
Also called scleroproteins,occur only in
animals donot occur in plants.
Include collagen,keratin and elastin.

56. COPOUND OR CONGUGATED PROTEINS
These are the proteins which in addition to
amino acids contain contain a non protein
group called prosthetic group in their
structure.
1.Nucleoproteins
Histones+nucleic acids
Most abundant in tissues having a large
proportion of nuclear material e.g
yeast,thymus and other glands and sperms.

57. 2.Phosphoproteins
Simple proteins+phosphoric acid
Examples casein of milk and vitellin of egg yolk.
3.Lipoproteins
Simple proteins+covalently bonded with lipid
substances like lecithin,cholesterol,triglycerides
and fatty acids.
Occur in blood plasma,nervous tissue,egg
yolk,milk and cell membrane.Bacterial antigens
and viruses also contain lipoproteins.

58. 3.Carbohydrate containing proteins
 Proteoglycans,glycoproteins(immunoglobulins,comlement many
enzymes).
4.Chromoproteins
 Proteins+coloured pigments
 HEMOPROTEINS
Hemoglobulin
Cytochromes
catalase
Peroxidase
 OTHERS
Flavoproteins
Visual purple

59. 5.Metalloproteins
Proteins+metallic atoms
Examples,Ferritin(Fe),Carbonic
anhydrase(Zn),Ceruloplasmin(Cu).

60. DERIVED PROTEINS
Include proteins derived from simple and
conjugated proteins.
1.Primary derived proteins
Synonymus with denatured proteins.
Denaturation takes place when some or all of
the cross linkages which normally keep the
molecular of protein intact are split,although
there is no hydrolysis of protein molecule.

61. Denaturation may be brought about by
chemical or physical agents such as heat,X
rays,ultrasonic waves,shaking or stirring for
long time,extremes of pH,salts of heavy
metals,neutral chemical agents such as urea
and organic solvents such as alcohol and
acetone.
In most cases denaturation is irreversible,but
in some cases it is reversible
Example,RIBONUCLEASE.(Denaturation is
reversible)

62. Secondary derived proteins
These substances are intermediates formed in the
progresive hydrolysis of protein molecule.They are of
different sizes and different amino acid composition.
PROTEOSES
Soluble in water,coagulated by heat,and are precipitated
from their solution by saturation with ammonium
sulphate.
PEPTONES
POLYPEPTIDES
OLIGOPEPTIDES

63. Classification based on function.
Catalytic proteins
Regulatory or hormonal proteins
Transport prpoteins
Immune proteins
Contractile proteins
Genetic proteins

64. Classification of proteins regarding
nutrition
HIGH QUALITY PROTEINS
LOW QUALITY PROTEINS