PROTEINS

Proteins
DEF:- chemically protein is a polypeptide
of 30-50
- amino acids, i.e
amino – carboseylic acid joined together
lay peptide linkage. It is the most impt
of all the agonic subs. And no life is
possible with out it.
Composition:- mainly it is composed of c,
N2 , O2, H2 and S. but some proteins
contain P, Fe, I2 ,Cu, Mn, Zn ++ . And
other elements.

Sources:- Aminal :- Egg, Fish, Poultry,
Meat, Milk cheese.
Plants:- Peas, Nuts. Soya beaus,
Potatoes,
Storage:The
capacity
of
lining
organisms. for storing proteins is limited
and relatively small as compased to its
capacity for string CHO and Fats.
Although many plants and may bacteria
are capable of synthesizing protein from
simple orgamic and inorganic compels;

but this capacity is least in higher animals.
Requirement:- 1 gm/ Kg of body mt (double
for children) or 46 gm / 70 kg body wt for
adults.
Functions:1. Catalytic :Most of the enzymes are
protein in nature. They catalyse various
reactions e.g.. Pepsin, trypsin, clnymo
trypsin.
2.

Proteins take an essential part in the formation
of protoplasm.

3. Proteins are an integral of all viruses which
are very imp. From pathogenic point of
view.
4. Protective and defensive function. The
immunoglobulin form defensive function.
5. Muscle contraction and expansion are in
every movt. me make. Muscles are made
up of proteins ACTIN and MYOSIN .
6. Transport:- Proteins act as carrier of many
subs. e.g.. Hb carry O2 and Co2. serum
albumin carry fatty acids; bilirubin. Other
proteins carry Fe, Cu, and Vit. A .

7. Structural function:- 3 imp. Structural
proteins are:i. Keratin :- which is the chief constituent
of hair, skin and nails.
ii. Collagen:- in connective tissue.
iii. Elastin:- Ligaments contain elastin.
8. Proteins are responsible for maintenare
of osmotic pressure. and PH due to
colloidal nature.

9. Hormonal function:- Most of the
hormones are protein in nature e.g..
Insulin, Growth hormone, parathyroid,
adrenocorticotropin hormone (ACTH) .
10.Nutrient and storage function. Some
proteins store material like starch.
and glycogen store energy e.g casein
in milk, ovalbumin in egg. Ferritin in liver
store iron.

10.a .a
Peptide reside
Poly ‘’ > 10 a . a reside
Pr . * with md. mt 7

Structure:-

NH 2
│
R ─ C ─ COOH

Side chain

C-

│
H

+

NH3
│
R ─ C ─coo
│
H
Ionic from

Free carboxylic gp.

R O
H R O
│ ││
│ │ ││
H2N ─ C ─ C ─ OH + H N ─ C ─ C ─ OH →
│
│
H
H
Free amino gp.
+HO2
R O H R O
│ ││ │ │ ││
H2N ─ C ─ C ─ N ─ C ─ C ─ OH → Dipeptide
↓
contain one
Peptide linkage.
Linkage.
l. e

Classification:1.
2.
3.
4.
5.

Proteins are classified
depending upon:Biological value.
Function.
Structure.
Physicochemical properties.
Solubility .(some proteins are hydrophilic
and some are hydrophobic ).

I
BIOLOGICAL
NOTRITIONAL VALUES.

OR

Porteins are divided into 2 gps.
i. Complete or first class proteins also
called “ high biological valve. proteins”.
These are the proteins which contain
all the essential amino acids. in their
structure. ( essential a.a are those
which can not be synthesized in the
body but are present in the diet.) e.g
casein of milk, fish, meat and egg.

ii). Incomplete or 2nd class protein also
called “Proteins of low biological value”.
These are the proteins which do not
have all essential a.a in their structure.
Some a.a are missing and they are
known as “ limiting amino acids”. e.g
“Animal proteins” like gelatin lack
tryptophane which is an essential a.a.
“Plants” i.e. corn lacks lysine and
tryptophane. Rice lacks, Lysine and
threonine. Soya lacks, methionine.

II CLASSIFICATION DEPENDING UPON
FUNCTION:1. Catalytic proteins:- e.g enzymes i.e.
trypsin, pepsin, chymotrypsin. etc.
2. Regulatory or hormonal:- e.g Insulin
GH , ACTH.
3. Structural proteins:e.g collagen
elastin and keratin.
4. Transport protein:- e.g.
transferin.
(Fe) ceruloplasmin (Cu).

5. Immune proteins:The defensive
mech is made by immune proteins e.g ɣ
- globulin .
6. Contractile proteins:- e.g Actin and
myosin.
7. Genetic:- DNA and RNA both contain
proteins in combination with nucleic
acid. These proteins are Histones and
protamines.
8. Storage:- e.g casein in milk, Gluten in
wheat, Zein in maize. Gliadin in wheat.

III
CLASSIFICATION
DEPENDING
UPON STRUCTURE:-

STRUCTURE:- ( Soluble non structural )
i. Globular proteins:- Also known as
“non- structural proteins”. The axial ratio
( i.e. ratio of length to width ) is less
than 10 and usually b/w 3-4 molecules
of protein is compact and poly peptide
chains are coiled e.g. Insulin, plasma
albumin , globulin enzyme protein, Hb
and Imoglobulin.

ii.

Fibrous protein or structural protein
(Insduble) they have axial ratio greater
than 10. the polypeptide chains are
coiled in spiral or helical . These are
long thread like mol. Whose helical
strands form fibers or sheets . e.g.
keratin, collagen, myosin and fibrin.

DEPENDING
UPON
PHYSICOCHEMICAL
1). Simple proteins.
PROPERTIES:-

2). Conjugated or compd pr.
3). Derived proteins.
1). Simple proteins:On hydrolysis only give a. a or their
derivatives and are of 2 types depending
upon shape and size of poly peptide
claims.
i). Globular pr. ii). Fibrous pr.

i). Globular proteins:- All enzymes are
globular proteins and include a large no.
of proteins. e.g. .
a). Albumin:- these are soluble in H2O.
Sources:- Animal:- Serum album, of egg.
Plants:- Legumelin.
Properties:1. They are coagulated by heat.
2. Not ppted. by ½ sat. which (NH4) SO4.
3. They form 60% of total pr. And first
class pr. Plasma level 4.6 – 6.4 g%

b). Globulin:1. Insoluble in H2O and soluble by salt
soln.
2. Coagulated by heat.
3. Ppted by ½ sat. with (NH4)2 SO4.
plasma level. 1.2-2.3 g%.
Sources: Animal :- lactglobulin, myosin
in muscle, serum globulin, thyrolgobulin
of thyroid gland.
Plant-seed

C). Protamines:- Present in sperm cells,
are rich in argenine. and are basic in
nature. Also have tyrosine and
tryptophane .In combination with RNA
form nucleo pr.
d). Histones:- Soluble in H2O. Rich in
arginine, basic in nature. Combine which
DNA to form nucleoproteins or nucleo
Histones. Which are present in cell
nuclei and form chromatin material.

e). Globins:- Rich in a. a histidine not
basic in nature. They combine with
haem – which
contain from and
tetrapyrol sing- to form Hb and
myoglobin. Diff . Species of Hb differ
only in globin while haem portion is the
same.
f). Plant proteins are Glutelins e.g. gliadin
of wheat and zein of maize.

2. Conjugated or compound
proteins:-

Proteins combine with non protein
part i.e. organic and inorganic that are
called prosthetic groops. Prosthetic
parts are covalently bound to the
proteins and they are necessary for their
function if the prosthetic group is
removed from the protein then the
protein has no function. They are further
÷ed x sub classes acc to their prosthetic
gp.

Phosphoprotein.
2. Muco protein or glycoprotein.
3. Nucleo protein.
4. Chromo protein.
5. Metalloprotein protein .
6. Lipoprotein.
1. Phospho proteins:- contain
phophorous. e.g. casein of milk,
ovalbumin. of egg. While some
enzymes (e.g. pepsin) are also
phosphoprotein protein.
1.

2. Mucoproteins:- They contain CHO or
Mucopolysaccharides. The CHO part is
attached to serine, asparagines or
threonine. They are viscous in nature
due to which they act as lubricants and
have a protective function. e.g. mucosa
in respiratory tract is a glycoprotein and
it protects it from bacterial invasion.
Gastric and intestinal mucus protects
the gastric mucosa from erosive action
of HCl. The irritation of gastric

Mueasa, hyperacidity or vagal stimulation
↑se mucus secretion. Blood group subs.
are also mucoprotein in nature. Cervical
mucus protects the uterus against the
invasion of microbial flora.
3. Chromoproteins:- These are the compds.
of proteins with pigments such as haem
and include Hb and cytochromes. Other
e.g. are the enzymes e.g. Flavoproteins –
contain flavin pigment. Visual –lodopsinpresent in eye visual purple – Rhodopsin –
present in eye. The prosthetic gp is
carotene (VtA).

4. Nucleoproteins:- contain CHO, H3 PO4
and nitrogenous base (purine and
pyrimidine) and pr. DNA and RNA.
These 2 nuclear acids are formed by
nitrogenous base which may be purine
or pyrimidine.
Sugar and H3 PO4
complex. They are present in cell nuclei,
protoplasm of cell, glandular tissue i.e
thymes, pancreas etc.

5. Metalloproteinase:- are the proteins in
combination with metals. Metals are
necessary for their action. e.g. enzymes
alcohol dehydrogenate has Zn as
prosthetic group. If Zn is removed.
The enzymes will have noactivity.
Important enzymes which have metals
as their prosthetic group are:Phosphotronsferase
Mg
Tyrosinase
Cu

Ceruloplasmin
Cu
Carbonic an hydrase
Zn
Arginase
Mn
3. Derived Proteins:- They are derived.
from simple or compound proteins by
various chemical reactions. They are of
2 types:- i). Primary derived proteins.
ii). Secondary derived proteins.

i). Primary derived proteins:- also called as
denatured proteins , in which some or all
cross linkages which normally keep the
molecular structure intact are broken.
Denaturation controls all the functions of
proteins e.g. solubility, enzyme activity,
specialized role if any. In primary derived
proteins primary structure is retained. and
esp. zndry and tertiary. structure is
disturbed. Denaturation may be reversible
or irreversible depending upon the
denaturing agents. and the extent of
denaturation.

Denaturing agents may be physical or
chemical such as:- • x- rays, • vigorous
shaking heat and light, low pH, salts of
heavy metals like PbCl2, HgCl2
denaturation ↓es solubility so the
denatured protein is easily coagulated at
isoelectric pH. (the pH at which amino
acid has no charge). Denaturation of
dietry protein is useful: denatured
proteins are more easily digestible. Imp .
e.g. are – cooked egg albumin . –
cooked meat proteins.

ii) Secondary derived proteins:Are formed by hydrolysis of simple or
conjugated proteins by acid or enz. e.g.proteoses- peptones – polypeptides.
And – oligopeptides, acc to their mol.wt.
Proteoses:- They are insoluble in H2O –
they are not coagulated by heat – they
are ppted by ½ and Full sat. with (NH4)2
SO4.

Peptones:- They are formed by hydrolysis
of proteoses.
-They are soluble in H2O.
-They are not coagulated by heat.
-They are not ppted by”(NH4)2 SO4”but by
special ppting agent i.e phosphotungstic
acid .
Polypeptides:- They are formed by
hydrolysis of peptones.
The mixture of above is obtained. by

digestion of proteins by enzymes.
Simple Proteins:- ( c globular proteins)
Fibrous Proteins:- They are large mol. and
composed of 2 or more poly peptide chains
which are coiled around each other.
Fibrous pr. are basic structural elements of
connective tissne imp. e.g. are:-Collagen:- are present in C.T thorough – out
the body. e.g. Skin, bone and tendon. It is
resistant to proteolytic. enzymes like
“pepsin” and “trypsin.”

They are converted to easily digestible
soluble proteins like gelatin by boiling
with H2O HCl, and alkali. It contains
proline, glycine, hydroxyproline. and
very small ant of tyrosine. It contains no
tryptophane.
Elastin:- are extracellular fibrous protein
and occur in elastic tissues e.g.
“tendons and arteries”. It is not
converted to gelatin and has little or no
Hydroxy proline the elastic tissue is a

mixture of “ elastin”, “collagen” and CHO
containg protein called “elasto mucin”.
Keratin:- it occurs in animal skin, nails,
horns, hoofs, hair, wool, feathers etc, to
which it gives strength. Keratin is found
with in the cells. It is insoluble. in H2O,
organic solvents, and in dil. Acids and
alkalies. It has high Cystine content
forming cross-links b/w peptide chains
which provide. strength to its mol.
Chemically keratin is quite inert and
resistant.

Lipoproteins:Diseases
due
to
lipoproteins.
Hyper lipoproteinemia:- It is the clinical
finding of high conc of particular class of
plasma lipoprotein. They are of 5 types
and these are type I ,II ,III ,IV, V.
Type I:- are rare disorder in which only
chylomicron. fraction is ↑ed abnormally.
This type of disorder occurs in patients
with genetic deficiency of “lipoprotein
lipase” in adipose tissue.

Type II:- are ↑ sed β – Lipoproteins. It is
due to low density density lipoproteins or
both VLDL and LDL. This type of
disorder occur both in hereditary form
and acquired form. These patients have
↑sed risk of atherosclerosis of coronary
arteries and ↑ed amt. of cholesterol.
Type III or β Lipoproteinemia:- it is a rare
disorder due to presence of abnormal
lipoprotein in plasma. It is the hereditary
form and sometimes it is due to zndry

effect of “hypothyroidism”. These
patients show early atherosclerosis and
have ↑ed risk of vascular disease.
Type IV. or pre –β – Lipoproteinemia:- It
is due to ↑sed amt of VLDL. It is
hereditary form and is found in patients
who are over weight. It is seen in
patients who have a tendency towards
diabetes M.
Type V.:- It is rare and appear zndry to
diabetes mellitus pancreatitis. It is
characterized ↑ed chylomicron and LDL.

Hypolipoproteinemia:- It is a genetically
transmitted disease and is due to
absence of “ chylomicron.” “LDL” “VLDL”
which is due to inability to synthesize
“apolipoprotein”pr.
Type
which
combine with lipid part.

Properties of Proteins
1.
2.

3.

They form colloidal soln. Of “hydrophilic
type”
They have “amphoteric.” property. They
combine both with acid and alkali to
form ionizable salts.
On hydrolysis give crystalline subs. Of
specific composition known as amino
acids.

4. For every protein there is a definite
characteristic pH. Known as “isoelectric
pH”. at which particles are neutral. Also
known as “lsotonic point” or “isotonic
pH”. All proteins are least soluble at
isoelectric pH. But certain proteins like
“gelatin” and “ovalbumin” remain in their
soln from.
5. Optical activity is due to the presence of
asymmetric C- atom and have the

property to rotate the plane polarized
light.
6. Diff. pr. Have diff. md. wt. depending on
this property, diff. pr. Can be separated
by a technique known as “ultra
centrifugation”.
7. Dialysis:- proteins cant pass through
semi permeable memb (like cellophane)
depending upon this property dialysis
can be used to serarate. Pr. From.

Crystalloids which can pass through.
8. “Buffer action.” (resistance to change in
pH) Proteins form very good buffer
pairs:. They are present in salt form as
well as acid form. They can act as
buffers on both sides of isoelectric point.
“Haemoglobin” is the best buffer in
blood. At physiological pH proteins are –
-vely charged ions. At isoelectric point
the pH is neutral.
Na Pr , K. Pr . K. Hb
Bld p.H
H. Pr H.Pr
H.Hb.
7.34-7.43

9. Hydration property:- protein in aq.
Media holds certain amt. of H2O due to
formation of H- bond b/w H2O and pr.
Polar gps. Like NH2, COOH, OH,
CONH2 form hydrogen bond.

H
│
R─ C ─ COOH
│
H─ N ─ H
amino acid

Hydrogen bond.

H
│
+
R─C─CO ─ H ─
│
+
H─N─H
H
│
+
H─O
H
+
H

O

In this way pr. From a shell of H2O
oround it.
10. Precipitation of Pr:- It is not a chemical
change. There is adsorption of one ion
on the other.
- Proteins are ppted from soln by salts of
heavy metals like HgCl2 AgNO3,
CuSO4.

-

-

Pr. Are ppted by certain acids which are
called alkaloidal reagents like picric acid,
Phosphotungstic acid, tannic acid and
H3PO4 in the basic medium.
By conc soln of such salts like, (NH4)2
SO4 , Na2 SO4 and Na Cl.
Pr. Are also ppted by dehydrating
agents like methyl and ethyl alcohol.

Mechanism:-

By neutralization of charges:- it results
in decrease in repulsion.
By removal of shells in which H-bond is
broken.
Proteins form colloidal sol. Of the type
called “emulsoid”. The most imp
property of emulsoid is that they have 2
stability factors. “Charge and hydration”
either of which is capable of keeping the

protein md. in soln. individual proteins
show marked difference in the hydration
of their particles.

MECH OF PPTION:+ Ve Pr (emulsoid )

+
+

++

acid

+
+

Pr. Care
Shell of H2O
-

++

Dehydrate
++

-

-ve protein
-(emulsoid)

dehydration

+

+ alkali or

+

electrdyte
+

+ +
+ ve Pr. Suspenoid ppt.

Acid or
Elector lyte

Suspenoid
-velycharged
protein

Solubility of pr:- Depends upon
distribution
of
hydrophobic or
hydrophilic groups.
If more hydrophilic groups are present on
the surface then it is more soluble.
On the other hand if more hydrophobic
groups are present on the surface then it
is insoluble.
Denaturation :- Protein is called “native
protein”
if
its
structure
remain
unchanged. From the natural state.

This property controls all the function of
protein. It its structure is changed it is
called “denaturation”. It occurs when
weak forces which are responsible for
secondary, tertiary and quaternary
structure are disturbed that results in
unfolding and uncoiling of protein
molecule. Which is responsible for
change in physical and in some
chemical properties. It is caused by:-

- Heat which causes splitting of salt
bridges by thermal agitation .
- By vigorous shaking and stirring.
- By ultraviolet radiation .
- Ultrasonic rays which destroy the ring of
aromatic a. a.
- By mineral acids and alkalis.
Denaturation maybe “reversible” or
“irreversible” depending upon the
denaturing agents and extent of
denaturation. From biological point of
view denatured proteins are useful . .

they can be digested easily.
AMINOACIDS (AA)
Amino acids are organic subs. Containing
an amino (NH2) and carboxylic gp
(COOH) these are basic units of
proteins. in nature 300 amino acids are
found but only 20-22 aa are involved in
protein formation which are
- amino
acids and these are called stand and
primary or normal amino acids.

Biomedical Importance of aa.
1.

2.

3.

Some a a have highly specific function in
the body e.g. citruline or ornithine they are
present in liver and they form urea from
NH3
G. A. B. A:- Gama amino butyric acid. It
is present in brain and other tissues. It
acts a neurotransmitter .
D O P A :- Dihydroxy phenyl alanine. It is
found in tissues during the metabolism of
tyrosine and phenylalanine .

It is used in the treatment of
parkinsonism .
4. Decarboxylation of a a give compounds
like Histamine which is a vasodilator.
5. Abnormal transport of a a in cell and
excretion in urine give disorder called
Amino acid uria.
6. Iodinated a a is useful in synthesis of
thyroid hormones T3 – T4 .

Structure:Gen . Formula .
NH2
│
R ─ C ─ COOH
│
H
(having both the charges)

COOH
│
H ─ C ─ NH2
│
R or H
- amino acid
All natural a a
Are
- aa

COO
│
+
H ─ C ─ NH3
│
R Hermaphrodite
Zwitterions
Ampholyte
or
Dipole

All a.a have a symmetric c- atoms. in their
structure i.e why they have the property to form .
Isomers.
L- NH2 gp is on left
D. NH2 towards right
COOH
COOH
│
│
NH2─C─ H
H─ C─NH2
│
│
CH3
CH3
D (-) alanine levorotatory

L (+) alanine dextrorotatory

All AA except glycine have isomers and
are optically active. The designation of
AA to D or L is derived from the compd
D and L form of glyceraldehydes NH2 if
it is on the right side then it is D NH2 “
“ “ “ “ left “ “ “ “ L D – alanine rotates
the plane polarised light towards left
and L alanine is dextrorotatory:. It
rotates the plane polarised towards
right.

CLASSIFICATION OF AA:I)

Acc to the structure
II) “ “ “ Polarity of side cham
III) “ “ nutritional valve
IV)“ “ Metabolic products formed in the
body
V) “ “ their affinity for H2O i.e hydrophilic –
hydrophobic .

Acc . To their structure:They are further ÷ ed x following
I. Neutral ─ Aliphatic
Aromatic
S- containing
Heterocyclic
2. Basic
3. Acidic
4. Imino acid
I)

NEUTRAL AMINO ACIDS:They are monoamine monocarboxylic
acid with a side chain which may be
aliphatic, aromatic or cyclic Acc to the
nature of side chain aa are further ÷ ed x
:a. Aliphatic aa
b. Aromatic aa
c. Sulphur containing aa
d. Heterocyclic aa.

aliphatic a a :- They have aliphatic
side chain which may be straight or
branched. e.g.
i). Glycine:- Simplest aa and has no a
symmetric c – atom.
NH2
│
H ─ C ─ COOH
│
H
a.

ii). alanine :- (Ala ; A)
NH2
│
CH3─ C ─ COOH
│
H

iii). Serine :- ( ser ; S)
NH2
│
CH2 ─ C ─ COOH
│
│
OH
H

iv). Threonine :- (The; T)
NH2
│
CH3 ─ CH ─ C ─ COOH
│
│
OH H

V). Valine :- (Val ; V)

CH3
CH3

H NH2
│ │
C ─ C ─ COOH
│
H

Vi). Leucine :- (Leu ; L)

CH3
CH3

H
NH2
│
│
C ─ CH 2 ─ C ─ COOH
│
H

Vii). Iosleucine :- ( lle ; I)

CH3
C2 H5

H NH2
│ │
C ─ C ─ COOH
│
H

b). Aromatic amino acids :- They have
phenyl or hydroxyphenyl ring in their
structure.
viii). Phenyl alanine:- ( Phe; F)

NH2
│
─ CH2 ─ C ─ COOH
│
H

ix). Tyrosine :- (Tyr ; Y)

HO ─

NH2
│
│
H

C) Sulphur Containing a a :- They are :x). Cysteine :- (Cys ; C)
NH2
│
CH2 ─ C ─ COOH
│
│
SH
H

Tow mol. Of Cysteine are linked through
–s –s – linkages forming cystine
Cysteine :NH2
NH2
│
│
COOH ─C─CH2 ─S─S─CH2 ─C─COOH
│
↓
│
H
H
Disulphide linkage.

Methionine :- (Met ; M)
NH2
│
CH3 ─ S ─ CH2 ─ CH2 ─ C ─ COOH
│
H

d). Heterocyclic a a :- which have indol in
their structure:Tryptophane :- (Try; W )
NH2
│
│
N
H
│
H

BASIC AMINO ACIDS:They have more than one amino group
in their structure e.g. arginine, histidine,
lysine, Asparagine, glutamine.
Glut amine
O
NH2
││
│
NH2 ─ C ─ CH2 ─ CH2 ─ C ─ COOH
│
H

ACIDIC AMINO ACID:- They have more
than one carboxylic group i.e – COOH
e.g. Aspartic acid, glut amic acid.
Glut amic acid:NH2
│
HOOC ─ CH2 ─ CH2 ─ C ─ COOH
│
H
-

Imino acid :- They have imino (NH) gp.
Instead of (NH2) group in their structure
e.g. praline it is a derivative of pyrolidine
and is an e.g. of cyclic a.a. In some cases
proline
is
hydroxylated
to
form
Hydroxyproline and usual form is 4Hydroxyproline .
Proline
4- Hydroxyproline.
HO─ 4
3
- COOH
²─¹COOH
-

N
│
H

N
│
H

-

SPECIAL AMINO ACIDS :- They are
not imino in protein formation but play
very imp. role and have highly specific
functions e.g. G A B A – acts. as
neurotransmitter D O P A – in t/m of
parkinsonism .
Iodinated a.a i.e Monoiodotyrosin Diiodotyrosine, tri – iodotyrosine (T3) and
tetra iodotyrosine (T4) clinically T3 and
T4 are used in finding the disease of
thyroid.

II). ACCORDING TO POLARITY OF RGROUP AT PH 7.0: amino are again
÷ed x 4 sub- groups:1. Non polar R – group.
2. Polar but uncharged R- group.
3. -Vely charged R- group.
4. +Vely charged R – group.
- NON POLAR R – GROUP:e.g. Alanine, leucine, Ioseucine,
Methionine , phenylalanine, proline,
Tyrosine, Valine.

-Polar but uncharged R - Group:e.g. serine, threonine, tryptophane,
Cysteine.
-Negatively charged R - Group:e.g. Aspartic acid, Glutamic acid.
-Positively charged R- Group:+ve
charge is due to the presence of an
additional group. e.g. Lysine, Arginine,
Histidine.

iii). Classification Acc. to
nutritional value:-

Was given by Black in 1956. a.a have
been ÷ ed x 3 gps.
Essential a.a or indispensible a.a .
Non “ “ “ dispensable a.a.
Semi “ “ “ Semi indispensable a.a.
Essential a.a or indispensible a.a.
Are those a.a with are not synthesized
in the body by any organic subs.

but must be present in the diet. For adults
8. a.a are essential and for children 10 a.a
are essential. They are:• Threonine • Tryptophane • valine .
• Leucine • Isoleucine • Methionine
• Phenylalanine • Lysine • Histidine and
• Arginine. (in children ).
- Non Essential a . a :- They can be
synthesized in the body from other organic
amic subs. e.g. Glutamic acid; Aspartic
acid,• Asparagines, • Alanine,• Proline, •
Hydroxy proline; • Glutamine, • tyrosine,
•Cysteine; serine.

Semi Essential a.a :- some of them are
synthesized in the body, but the amt. is
not enough to meet the reqmt. e.g. ;
Arginine ; Histidine.
iv). Classification
acc to metabolic
products:- They are again ÷ed x 3 sub
gps.
a. Ketogenic a.a
b. Glucogenic a.a
c. Keto and glucogenic a.a.
-

a.

b.

c.

Ketogenic a.a :- on metabolism give
rise to ketone bodies e.g. acc to acetic
acids β- Hydroxybutyric acid,• Acetone.
Glucogenic a.a :- They give rise to
glucose and glycogen or subs. With
give these compds. e.g. • Alanine, •
Glycine, • Arginine, • Threonine, •
Valine, • Methionine, • Cysterin,•
Cystine , • Histidine, • Proline,
•Hydroxyproline.
Keto and glucogenic
a.a:- e.g.
Isoleucine, Tyrosine, Tryptophane.

v).Classification
affinity for H2O:-

-

-

Acc

to

their

They are ÷ ed x 2 groups
side chain
charged at pH6
“ “ un “ “ “ “
Side chain charged at pH6 are called
Hydrophilic .e.g. •Lysine, • Arginine, •
Histidine, • Asparginine, • glutamic acid.
Side chain uncharged at pH6.

Hydrophobic
Alanine
Valine
Leucine
Isoleucine
Proline
Phenylalanine
Tryptophane.

Hydrophilic
Glycine
Serine
Asparginine
Glut amine
Cystine
Threonine
Methionine

Properties of amino acids physical
properties:1.
2.
3.

These are white crystalline subs.
Crystalline forms are sp. for a.a.
Solubility :- they are soluble in H2O
acids and alkalis.
Melting point:- Diff .a.a have diff,
melting points . And decompose at or
near its melting point. They have high
melting point so large amt. of energy is
required to disturb the forces of its
crystalline structure

4. Optical activity:- all amino acids except
glycine possess at least one a symetric
C- atom in their structure and the no of
possible stereoisomer will : be at least 2.
the configuration of amino group- NH2
around the asymmetric C – atom is used
as reference just as the configuration of
OH around the asymmetric c – atom of
glyceraldehydes is used reference for
sugars.

COOH
COOH
│
│
NH2 ─ *C ─ H
H ─ *C ─ NH2
│
│
H ─C─H
H─C─H
│
│
OH
OH
L – Serine
D – Serine
* Asymmetric C – atom

5. Taste :- some a.a are sweet in taste
like glycine and alanine. Some are
tasteless like Leucine. Some are bitter in
taste e.g. Isoleucine and Arginine.

Chemical properties:Acid / properties of amino acids:Amino acids in aq. Soln contain weakly
acidic α - carboxylic groups and weakly
basic α- amino groups. In addition, each
of the acidic and basic amino acids
contains an ionizable group in its side
chain. This both free amino acids and
some amino acids combined in peptide
Linkages can potentially act as buffers.

A buffer is a soln which resists any change
in pH when an acid or a base is added
to it. A buffer is made by equal amts. Of
weak acid and its conjugate base. The
quantitative relationship b/w the [ ] of
weak acid (HA) and its conjugate base
(A) is determined by handerson
hasselbalch equation i.e.
pH =
pKa +
Log base
acid

Titration curve of acetic acid:The Handerson- Hasselbalch equation
can be used to calculate the pH of a
soln containing a weak acid after the
addition of strong acid or base.
OH HO
2

CH3 COOH
I
Aceticacid ,HA

CH3 COO
H+

II
acetate , A

If acid is added CH3COO can neutralize
and if base is added then CH3COOH can
neutralize and dissociate into CH3 COO
and OH to form H2O. Thus a soln
containing acid and base with a . pKa 4.8
resist resist a change in the PH from 3.85.8 with max. Buffering at pH 4.8 which is
pka. A conjugate acid/ base pair can serve
as an effective buffer when the pH of a soln
is with in approximately + 1 pH amt of the
pKa of the weak acid.

Whereas max. Buffering capacity occurs
at a pH equal to the pKa. At pH values
less than the pKa the protonated acid
form is predominant. At pH values >er
than the pKa the deprotonated form is
predominated.

Eq. of OH- added

Buffer region
1.0

[ II ] > [ I ]

[ I ]-[II]
[ I ] >II

0.5

pka = 4.8

0
0

3

4 5

6

7

pH
Titration cure of acetic acid

Titration of alanine
1.

Dissociation of the carboxyl group:- alanine
contains both a carboxyl and NH2 gp. At a
low or acidic pH both of these groups are
protonated. As the pH of the soln is raised
the – COOH group of form I can dissociate;
by donating a proton to the medium and
results in the formation of the carboxylate gp;
- COO . Which is the dipolar form of the mol.
also called Z witterions with no charge and is
the isoelectric form of alanine with an over all
charge of zero.

Handerson Hassalbalch equation is
used to analyze dissociation of – COOH
gp. So pH = PK, + log II
I
2. Dissociation of NH2 gp:NH3 is a much weaker acid – than –
COOH gp. Release of proton from the
protonated amino gp. form II results in
the fully deprotonated form of alanine i.e
form III.
+

This sequential dissociation of COOH and NH3
from alanine is shown below:H
OH H2O
H OH H2O H
│
│
│
H3N ─C ─COOH →

+

│
CH3

-

H3N ─C─COO →

← H+
PK1 = 2.3

↓ I
Fully protonated
pH less than 2

│
CH3

←
H

+

Pk2=9.1

↓ II
Isoelectric pH6.
net charge 0

-

H2N─C─ COO

│
CH3

↓ III
pH 7er .10
Net charge-1

Each of the titrable gps has a pKa i.e
numerically equal to the pH at which
exactly ½ of the protons have been
removed from that group. The pka for
most acidic group (- COOH) is pK1 . Pka
+
for the next most acidic gp (-NH3 ) is
pk2.

Titration curve of
alanine:The titration curve shows the pH
changes during the addition of base to
the fully protonated form of alanine (I) to
produce the completely deprotonated
form (III) the – COOH /- COO pair can
serve as a buffer in the pH region
around pK1 and the – NH3/ - NH2 pair
can buffer in the region around pk2.

Region of buffering →

← region of buffering

Equivalents
Of OH added

[I ] = [III]
2.0

PI=5.7

1.5

pk2 = 9.1

[ I ] = [ II]

1.0

Pk1 = 2.3

0.5
0

2

4

6

8

10

pH

When pH = pK1 (2.3) equal amts of forms I + II of alanine
exist in the soln and when pH = pK2 equal amts of II and III
exist in the soln .

Isoelectric point :- At neutral pH, alanine

exists predominantly as the dipolar
form II in which the amino and
carboxyl gps are ionized but the net
charge is zero Isoelectric point is the
pH at which an amino acid is
electrically neutral i.e where the sum
of the +ve charges equals the sum of
the -ve charges . For a. a like alanine
which has only 2 dissociable
hydrogen's the PI is average of pk 1,
and pk2 i.e pl = 2.3 + 9.1 = 11. 4 = 5.7
2

This value is midway b/w pk1. and pk2 it
corresponds to pH where structure ll
predominates and at which there are
also equal amounts of form 1 and III.
At physiologic pH all a.a have both – ve
and + ve charged gps. And are dipolar,
ions . So they act as acid and base and
are known as ampholytes or amphoteric
electrolytes.

Titration of Histidine :- Histidine contains
3 chemical gps. eash of which can
reversibly gain or lose a proton; the
COOH gp
-NH2 gp and the imidazole
gp.

H
│
+
H3N ─C─COOH
│
CH2
│

HO

H
│
+
H2O H3N─C─COO
│
CH 2

│
HN

H2O

H+

C = CH
+

OH

│
NH
//

C
│
PK1 = 1.8
H
│
Net charge = +2

H+
│
C = CH
│
│
+HN NH

//
C
││

PK2=6.0

Net charge =+1

H
│
+
H3N─C─COO
│
CH 2
│
C= CH
│ │
N NH

/
C
│
H
│││
Net charge= 0
(isoelectric for)

OH

H2O

H+

PK3=9.2

H
│
H2N ─C─COO
│
CH2
│
C = CH
│ │
N
NH

//
C
│
H

Net charge = - 1

the addition of bore fully
Prorogated his result in
removal of COOH proton

pk1=1.8.the inidazole gp
pk2= 6 and nh2 gps 9.2
the I P can be calculated
by indentifying
zwitterion. Then average
.
So . x.
.

PI = pk2 + pk3 = 6+9.2 = 15.2 = 7.6
2
2.

2). Formation of peptide linkage or
bond:The amino acids are attached to their
neighboring acids by- COOH gp on one
side and by NH2 gp on the other with
elimination of one H2O mol. In this way
an acid amide bond is formed which is
called a peptide bond.

The general formula of peptide b/w 4 a.a residue
forming a tetra peptide is:
R O H O H R O H R
│ ││ │ ││ │ │ ││ │ │
H2N ─ C ─ C ─ N ─C ─ N─ C ─C─ N─ C─COOH
│
│
│
H
H
H
Side containg free
side containg
amino gp
free carboxyl gp.
O H
││ │
The bond ─ C ─ N ─ is the peptide bond and in the
above formula there are 3 such bond joining 4 a.a
and a tetra peptide is formed.

Peptide of more than 10 a.a. are called
polypeptides. Following reactions are
used for detection and measurement of
a.a.
Ninhydrin reaction :- All a.a having one
free NH2 and COOH gp give purple or
blue gp on treating with Ninhydrin.
Reaction with 1 Floro, 2-4 dinitro
benzene:- dinitrophenyl derivatives are
formed when a.a are treated with
reagent.

Properties due to COOH group :1. Formation of esters:- Esters are
formed when a.a. are treated with Alfold
in the presence of H Cl.
2. Decarboxylation reaction:- when a.a
is treated in presence of Ba (OH). CO2
evolved in preside of decarboxylase in
body. Histidine CO2 Histamine
decarboxylase

(Vasodilator) .

Properties due to NH2 group:1. Acetylation:- when a. a are treated with
acetylating agents like CH3 COOH or the
amped which provide acetyl gp acetylation
takes plare COOH.
COOH
O
COOH
O
│
││
│
││
R─C─ NH2+CH3 ─C─ OH→R─C─ NH─C─CH+H2O
│
│
H
acetic acid
H acetylated acid
a.a

Addition of acetyl gp to the amino gp is called
acetion .
2. Methylation:- when a.a. is treated with
mettugl codide in alkaline soln. the product
formed is called bution and this property is
used for separation of a.a.
3. Reaction with Nitrous acid (HNO2):- is
used for determination of free amino gp in
a soln. in this reaction nitrogen is evolved
and Hydroxy acid is formed. a.a. + HNO2
oxidizing N2 Hydroxy acid.

4.

Reaction with. Form aldehyde:(HCHO)- COOH gp is easily titrated
against alkali in proenice of NH2 gp.1.
This amino gp is blocked by adding
formaldehyde. Then this COOH gp is
titrated against alkali this method is
called formyl litration method and is
used for determination of a.a. N2 in
ursine.

5. Colour Reactions:- are used for
identification and determination of
various a.a. chemical reagents are used
as sprays to develop chromatograph
chromatography is a technique for
separation and identifying defferent a.a.
1. Ninhydrin reaction:- It is used for
quantitative estimation of a.a. urine and
other biological fluids.
2. Biuret reaction :- It forms the basis of

quantitative and qualitative estimation of
proteins in blood and other finds
spectrophoto metrically. When urea is
treated at 18 ᵒC it gives a compd. Called
buried when biuret is heated with Co
So4 and a strong alkali it gives a violet
colour so any compd. When has 2 mol.
Of CO NH2, CH2 NH2) C (NH) NH2 in its
structure it gives this test +ve. At least 2
or more than 2 peptide linkages should
be present for +ve result of this test.

So its a general test for pr. Or a.a.
3. Xanthoprotein test:- is specific for a.a.
honing phenyl alamine.
i). p
Tryptophane and tyrosine.
4. Modified Millous test:- specific for
tyrosine due to presence of phenyl gp.
5. Nitroprusside test:- specific for a.a.
having S-M gp.
6. Sulphur test:- is +ve for a.a. containg
sulphur in in their stencture receipt
methionine.

Functions of amino acids:To maintain nutrition.
2. To maintain growth.
3. For life span.
CLINICAL SIGNIFICANCE OF AMINO
ACIDS:Many a.a. leave and enter the plasma
during normal metabolic processes a
few remain intracellular circulating a.a.
1.

are fittered at the glomerulus and are
largely reabsorbed in the tubule by
active transport and some a.a. are not
fully reabsorbed and appear in urine.
Diff a.a. are present in diff. [ ] . e.g.
glycive, histidive, alanine, serine – 1
mg /kg. others < 1 or 0.5 mg/kg e.g.
tyrosine valine, Levine, threonine.
Total amt. of a.a. N2 = 100-200mg/day
-300 mg/day. Excretion of >er amts . Of
a.a. urine is called amino acid uria. And

is of 2 Types:1. Overflow amino acid uria.
2. Renal amino acid uria.
1). Overflow a.a. uria:- There is some
sctrarenal metabolic defect as a result of
which there is some ↑se in plasma a.a.
of one or more a.a. which exceed the
capacity of normal renal tubule to
reabsorb them.
Causes:- i).Severe liver disease.
ii). Tissne masting condition like typhoid.

iii). Alkalosis. iv). Phenyl ketomria. V).
Maple syrup urine disease.
2. Renal a.a. uria :- In this plasma level of
a.a. is normal but • • of some failure of
reabsorption an ↑se amts of one or
several. .a.a. are excreted in urine
couses:- i). Defect in single transport
mach. ii). Generalized tubloular damage

Structure of proteins:Proteins have 4 types of structures:1. Primary.
2. Secondary.
3. Tertiary.
4. Onaternary.
1. Primary structure:- The sequence of
a.a. in a protein is called the primary
structure of pr.

many genetic disease result due to
abnormal a.a. sequences. If the primary
structures of the normal and the mutated
proteins are known, this information may
be used to diagnosed or study the
disease. Every protein and polypeptide
chain structure in biological organism
has diff. sequence of a.a. that all oms
the protein to carry out function. There
are 20 a.a. which enter into the
formation of peptide molecules hence x
the synthesis of protein molecules.

An unlimited no of peptide mol. Are
possible from 20 a.a. the no. of a.a. in a
peptide mol. Varies from a few to
several hundreds or more. Each protein
has its own specific sequence of a.a. for
e.g. Abnormal Hb which is HbS differ
from normal Hb in one respect i.e
glutamic acid. is replaced by valine at
position no.6 in HbS in β – chain. The
primary structure of proteins is
regmlated by the respective genes or

specific chromosomes. The numbering
of a.a. residues in a peptide chain starts
from the a.a. containg free- NH2 group.
So , In Hb
- chain has 141 a.a. β –
chain has 146 a.a. The charge in
protein properties depends upon the
kind of chain.
Ribonucleases (enzyme) contains
protein
chain
of
124
a.a.
Carboxypeptidase removes one terminal
a.a. remaining mol. Has same biological

function. Same is the case with diff. insulins
from diff. sources. Insulin of cattle or from
Hog or sheep differ only in position 8,9 and
10 of A chain and C terminal of porition 30
of β chain.
A chain = 20 + 1 21 a.a
A chain = 30 a.a.
A chain
β chain
8 – 9 10
30
Human = Thr – ser – lle
The
Hog
= Thr – ser – Ile
Ala
Sheep = Atre – Gly – Val
Ala

The primary structure of human Insulin –
ginners
as
s
s
↑
10 7
11
20 21
A chain
a.a. residue s -s
↑
7

- s-s
19

21
β chain

The insulin mol. Consists of 2 peptide chains
A+B containing 21 and 30 a.a. residue. These 2
chains are joined to other at 2 sites though
interchange – s – s – linkages of Cysteine

residues chain A has an interchange
– s – s – linkage b/w 2 Cysteine
residues present it No. 6 and 11
position. The beef and sheep insulins
differ form human insulin to 3 and 4 a.a.
respectively.
Despite of the light
difference, all linear insulin can be used
in human and perform save function as
human insulin, but some times a slight
change in a.a. sequence make a great
deal of difference. For e.g. two
hormones elution and vasopressin have

identical structure at position 3 and 8
but diff. biological activity. The primary
structure is regulated by specific gene in
specific chromosomes.
SECONDARY STRUCTURE:In this
structure proteins can fold or align
themselves such a manuer that certain
patteen repeat
themselves – these
repeating pattervs are called secondary
structure.
Important
secondary
structures absaued are.

1.
2.
3.

- Helix
Pleated sheet or β ─ structure.
Random coil in some protein.
- Helix:- is the most common and a
spiral structure, consisting of a tightly
packed, coiled polypeptide bark bone
core with the side chains of the
component a.a. extending outward from
the control axis. Keratins are a funnily
of closely related fibrous proteins,
whose structure is nearly entirely -

Helical. They are a major component of
hair and skin, their rigidity is determined
by the no. of disulfide bonds b/w
constituent polypeptide chain. On the
other hand Hb. Is approximately 80%
- helical is a globular, flexible molecule
helix stabilised by rctensine H- bonding
b/w peptide bond carbonyl oxygen's and
amide hydrogen. Each peptide bond
participates in H – bonding. Each turn of
an - helix contains 3.6 a.a. A helix

may be right handed or left handed.
A right handed helix is more stable
than the left handed. Certain a.a. in
protein which may interfere with
formation of certain structure e.g.
glycme and prolie these 2 a.a. present
the formation of
- helix.
β ─ SHEET OR PLEATED SHEET:It is a form of 2ndry structure in which
all the peptide bond components are
involved in H – bonding. The surfaces of
β - sheets appear “pleated” and these

structures are .: often called “ β ─
planted sheets.” β ─ sheets are
composed of 2 or peptide chains ( β ─
strands). Or segments of polypeptide
chains that are almost fully extended . In
β ─ sheets the H- bonds are
perpendicular to the polypeptide back
bone.

─ R ─ C─H
H─C
│
│
C
N

/
O─ ─ ─ H
O
H
│
//

N
C
│
│
H ─ C ─R
R ─ C ─H
│
│
// C ─ H - - - - - - - O N
│

│
C H

Hydrogen bond
b/w chains

A β - sheet can be formed from 2 or
more separate polypeptide chains. That
are averaged either parallel or anti
parallel to each other. The band are
teemed inter chain bonds when formed
b/w separate polypeptide chains. A β ─
sheet can also be formed by a single
polypeptide chain folding bark an itself.
In this case the H – bonds are intea
chain bonds e.g. are the globular
proteins.

C – Terminal

N – terminal

N terminal
Anti parallel
β ─ pleated sheet.
C – terminal

so β sheet are formed in fibrous and
proteins A no- of disease results in
deposition of fibrous protein for e.g.
ALZHEIMER’S disease. Which results
from deposition of amyloidal protein in
the brain tissue.
β ─ bends are generally composed of 4
a. a. one of which may be praline . G
lysine is also fond. Β bends reverse the
direction of a polypeptide chain this
forming
a
globular
structure.
Approximately one 1 of an average
2

Globular protein is organized x
repetetive str. Such as
- helix or β –
sheet. The non repepetetive 2mdry str.
Are not random and the random coil
refers to the disordered structure
obtained when proteins are denatured.
Globular proteins are constructed by
combing 2mdry str. Elements. i.e
helixes, β – sheet, non repetetive
sequence. And from the core region.

Tertiary structure of globular
proteins.
The primary structure of a polypeptide
chain determines is tertiary. The structure
of globular proteins in aqueous soln is
compost with a high density of atoms in
the core of the mol. Hydrophobic side
chains are buried in the centre and
hydrophobic groups are on the surface of
the mol. And are imbed in H – bonds.
Tertiary st. is a combination of
- Helices
and β- strands

Domains:- are fundamental functional and
3 duneirsion al structural imts of a
polypeptide. Each domain has the
characteristic of a small, compost globular
protein i.e structurally in dependent of other
domains in the poly peptide chain.
Interactions stabilising tertiary
structure:3 Dimensional structure of each polypeptide
is determined by it’s a. a. sequence.

1.

4 types of interaction cooperate in
stabinlioing the tertiary structure of
globular protein.
Disulfide bonds:- A disulfide bond is a
covalent linkage formed from the
sulfhydnyl gp. (- SH) of each of 2
Cysteine residue to produce a Cysteine
residue. The 2 Cysteines may be
separated by many a . a.
in the
polypeptide. Or may be located on 2 diff
polypeptide. The folding of the

polypeptide can bring the 2 Cysteine
residue = in proximity and permit
covalent bonding of their side chains.

H O
│ ││
N―C―C
│
│
H CH2
2 Cysteine
│
polypeptide
Residue
SH
back bone.
SH
│
H
CH2
│
│

N―C―C
│ ‖
H O
↓ oxidant for e.g. O2
H O
│ ‖
N―C―C
│
│
H
CH2
│

S
│ ← Disulfide bond.
S
│
H ― CH2
│
│
N―C
│
H
Cysteine residue.

2. Hydrophobic interactions:- Amino
acids with non polar side chains tend to
be located in the interior of polypeptide
mol. Where they associate with other
hydrophobic a. a. amino acids with polar
or charged side chains Thad to be
located on the surface of the mol. In
contract with polar solvent.
3. Hydrogen bonds:- A. A side chains
containing O2 or N2 – bond hydrogen,
such as in alcohol gp. Of serine and

threonine can form H – bonds with
election rash atoms, such as the O2-gp
of carboxyl gp or carbonyl gp of peptide
bonds .
4. Ionic interactions:- Negatively charged
gps such as carboxyl gp in the side
chain of aspartate or glutamate can
interact with the tuely charged gps. Such
+
as NH3 gp in the side chain of lysine.

glutamate
H H O
│ │ │
N―C―C
│
CH2
│
CH2
│
C

aspartate.
H H O
│
│
│
N―C―C
│
CH2
│
C
/

O
O

≡
H
│ H – Bond.
O
│
H
CH2
│
│
―C―C
│ ‖
H
Serine
H O

≡
NH3 chain bond
│
CH2
│
CH2
│
CH2
│
CH2 lysine
│
N ― CH2 ― C = O

QUARTERNARY ST.OF
Hb.





Hb. Tetramer is composed of 2 identical
dimes i.e (β )1 and (β )2.
2 polypeptide chains with in each dimer
are held to gather primoily by
hydrophobic interactions.
Inter chains hydrophobic interactions
form strong ass. b/w + β sub imts in
the divers. I one and H- bonds also
occur b/w the members of the dimmers.

In contrast the 2 dimmers are able to
many with respect to each other,
being help to gather primarily by polar
bonds.
 Weaker interactions b/w these mobile
dimers results in the 2 dimers
occupying diff. relative position in
deoxy Hb compared to oxy Hb.
R – Form:- The binding of O2 to Hb
courses rupture of some of the conic
bonds and H – bonds b/w the β

dimmers, leading to st called relaxed or
“R” Form in which polypeptide chains
have more freedom of in out and Rform has more affinity for O2.
T- FORM:- is the deoxy form of Hb. Also
known as “T” or taut form. The 2 β
,
dimers interact through a network of
ionic bonds and H – bonds that conation
the mout. of polypeptide chains. “T” form
is the low o – affinity form of Hb.

Quaternary structure of proteins:This structure is shown by there which
are made up of more one peptide chain
subunits each of which has its own
primary, zndry , tertiary st.e.g. Hb it
contains 4 chains . 2
chains with 141
a. a and 2 β chains with 146 a. a. these
- β chains enfold a harem gp. Which is
now in st. the may these 4 subunits
polymerize to form is called quaternary

structure . It determines now diff submits
fit x an orgamied mamer. Globin is a
protein of Hb and each globin chain
sareand a harem unit is called the
prosthetic gp. Similarly pycnic dehydes
grease ( enzyme) is formed by assembly
of 3 subunits.

COLLAGEN.
It’s a mall characterised fibrous protein
honing structure function in the body's is
the most abundant protein in the human
body. Collagen be dispersed as get that
serves to stiffer the structure as in the
extra cellular matrix or the vitreous
humane of the eye. In other tissues it
may be bundled in tight parallel fibers
that provide great strength as in
tendons.

In bone . In occurs as fibers arranged
at an angle to each other in order to
resist mechanical
sheer from any
direction. The polypeptide precursors of
the collagen mol. Are formed in the
fibroblasts
and
secreted
x
the
extracellular matrix. After enzyme
modification the mature collagen
monomers aggregate and become
crosslinked to form collagen fibers.

Structure of collagen:Types of collagen:- collagen mol.
Consists of 3 polypeptides called
chains which nrap aramd each other in
a triple helix, founding a rope like
structure. The 3 polypeptide chains are
held together by H – bonds
Collagen - chain .
b). Amino acid sequence :the primary structure of collagen is
a)

un usual in that glycine the smallest a. a
is frond is every zcd position of the
polypeptide chain. Glycine is a part of
repeating sequence – Gly – x – Y.
where
x
is
praline
and
is
hydroxyproline .
c). Triple helical structure :- collagen has
an elongated triple helical st. placing
may of its side chains on the outside of
the mol.

d). Hydroxyproline. and hydroxylyoine
one important in stabling triple helix st.
e). Glycosylation:- The hydroxyl gp of
hydroxylyoine of residues of collagen
may be hydroxylated.

Biosynthesis of collagen:Takes place nudes the following headings:1. Formation of pro
- chain.
2. Hydroxylation.
3. Glycosylation.
4. Assembly and secretion.
5. Extracellular cleange of pro collagen mol.
6. Formation of collagen fibrils.
7. Crors link formation.

1.Formation of pro

- chain:-

Functions outside of cells. Like most
proteins synthesised for report collagen
contain a special a. a at the N- terminal
of their polypeptide chain. This acts as a
“signal” that the polypeptide being
synttsred is destined to leaue the cell.
The signal facilitates the binding of
ribosomes to the R E S . And directing
the passage of the polypeptide chain x

the cistervae of R E R . And field a
precursor of collagen called a prochain.
2. Hydroxylation:- The prochain are
pro- cessed by a no . Of enzyme steps
with in the lumen of RER. While
polypeptides are still bring synthesised.
Selected proline and lysine residues one
hydroxylated, found in Y position of the
– Gly – x – Y - , to hydroxyproline and
hydroxylyoine residues.

Redniong agents like vit . C and mol. O2
is required in the reaction. With out
which the prolyl hydroxylase and hysyl
hydrooxylase are mable function. In the
case of ascorbic deficiency collagen
fibers can’t be cross linked greatly ↓ing
the tensile strength of assembled fiber.
Resulting. in disease called SCURVY.
3.
Glycosylation:some
of
the
hydroxylase residues are modified by
glycolylation with glucose or glucosylgalactase.

4.

Assembly and secretion:- after
hydroxylation and glycosylation, pro
-chain form pro collagen a precurson of
collagen that has a central region of
triple helix honked by the non helical
amino and carboxyl terminal retension
called pro peptides. The formation of pro
collagen begins with formation of inter
chain disulfide bonds b/w the C- terminal
extension of the pro - chain. This
brings the 3 chains x an alignment for

helix formation the pro collagen are
trouslocated to the Golgi app. Where
they are packed in secret ory vesicles.
The vesicles fuse with cell membrane
cansing a release of the procollagen
mol. X the extracellular space.
5. Extracellular cleavage of procollagen
molecule:The pro collagen mol.
Secreted into the extracellular space is
cleaned by N and C pro collagen
peptidases. Which remones the terminal

peptidase releasing the triple helix
collagen mol.
6. Formation of collagen fibrils:Individual collagen mol. Spontaneously
associate to form fibrils and subsequent
cross linking .
7. Cross link formation:- The fibrillar
array of collagen mol. Series as a
substrate for hysyloxidase which
oxidatinely denominates some of the
lysyl and hydroxylysyl residues in
collagen.

The reactive aldelydes that result can
condense with lysyl or hydroxylysyl
residues in neighboring collagen mol. To
for covalent cross – links.
DEGRABATION OF COLLAGEN:- in the
extracellular matrix is accompalished by
a family of collagenases. That cleave
intact collagen fibers x small fagments
that can be phagocytosed and further
degraded by lysosomal enzymes to their

constituent a. a.
COLLAGEN DISESES:- Defect in any
step in synthesis can result in genetic
disease involving an in ability of collagen
to from fibers with needed tensile
sliengtes.
For e.g. “EHLERS- DANLOS Syndrome”
in it the skin is stretchy and joints are
loose.

Osteogenic in perfecta:- also known
as brittle bone disease or syndrome
bonds can be easily bond or factual
resulting in retarded mind heading,
tinted
spice
and
humpback
appearance.

PLASMA PROTEINS
GENERAL CONSIDERATIONS:RBC
- Blood consists of i). Solid elements
WBC
ii). Liquid wedum
Platelets
i.e plasma
- Once the blood has coagulated the remaining
liquid phase i.e serum lacks the clothing factors
including fibrinogen .
- Serum
does contain some degradation
produets of clothing factors.

- Determination of [ ] various plasma

proteins has a diagnostic value.

Basic functions of blood.






Respiration i.e from lung to
tissues and CO2 from tissne to
lungs.
Nutrition transport.
Excretion transport.
Maintenance of N acid base
balance in the







Regulation of H2O balance.
“
“
body heat or
temperature.
Transport of hormones .
“ “ Metabolites.
Coagulation.

Basic characteristics of
Pl. proteins





Site of synthesis:- liver, plasma cells i.e
ɣ. end otherlial cells.
Mostly
plasma
proteins
are
glycoproteins •• of N or O linked
oligosaccharide chain. Albumin is not a
glycoproteins.
Haif hife is specific for specific plasma
protein Albumin and hepatoglobulin
have. 20 days and 5 days in N. adults.





“A cute phase proteins”, also known as
reactants and their level ↑es during
certain inflammatory reactions and Creactine proteins,
- antitrypsin,
hepato globin,
- 1 acid glycoprotein
and fibeniogen their level may ↑se to
50% - 1000 – fold and levels are also
↑sed in chronic inflammations and
cancer.
- 1 antitrypsin can neutralise certain
proteases released during the acute
inflammatory phase.

Functions of plasma proteins:functions
plasma
proteins.


Antiproteases



Blood clothing



Enzymes

Anticlrymotrypsin
1- Antitrypsin
2 – Macroglobulin
Antittrombin
various coagulation factory
fibrinogen.
coagulation factors








cholinesterase
aminotransferases.
Hormones
Erythropoietin.
Iumme defense
Imno globulins,
complement proteins,
β -2 u- globulins
Inflammatory Resp. CRP.
Oncofetal
1- fetoprotein.
Transport pr.
Albumin, steroids,
cemlo-plasma,

corticosteroid
binding globulin, hepatoglobin
lipopr., Rented binding ,
Thyroid birding globulins
transfers in.

1. Albumin.






Mol. Mt is 69 KDA.
Makes 60% of total plasma protein- 3.44.7g/dl.
Produced in the liver. 12 g/day
Albumin is initially synthesised as a prepr.
Its synthesis is ↓ed in various liner
disease .








A : G is ↓ed in liver diseases.
Mahumtrition – kwashiorkor- ↓ed
synthesis
Consists of one polypeptide chain 585
a.a
• • of its lomer mol. Mt and ↑ [ ] it is
thought to be responsible for 75-80% of
the osmotic pressure of humor plasma.
Anolbumiemia – lack of albumin with
moderate edema.



Albumin as transporting / binding protein
FFA, Ca, certain steroid hormones
bilirnbin, Cu , dings e.g. sulfonamides
penicillin G, Aspirin etc.

2. Hapto Globin.






Plasma
glycoprotein
that
binds
sctrcorpuscular Hb in a tight non
covalent complex.
Approximately 10 % of Hb that is
degraded each day is released X the
circulation and is this sctracorpnscular.
Free Hb parses through the glomerulus
of the kidney, enters the tubules and
tendon to ppt. therein.



however the Hb- HP complex is too
large to pan through the glomerulus.
The function of Hb this appears to be to
present low of free Hb X the kidney. This
consumes Fe present in the Hb.

3. Transferrin.




It’s a glycol pr. Synthesized in liver is a β
1 – globulin with a mol. Mons of app. 76
K Da.
3+
It transports one iron atom as Fe, mo no
ferric form or 2 iron atoms as Fe 3+di
,
ferric form premed of transferrin in the O
to sites where iron is reqd. e.g. from the
gnt to the bone marrow and other
organs.

4. Ceruloplasmin.




Mol. Mars 160 K D a – an
2- globulin,
90% Cu is carried by it in the plasma.
And has a blue colour • • of its high Cucontent
Each mol. Of cernls plasmin binds 6
atoms of Cu very tightly, so that the Cu.
Is not readily exchangeable. Album
carries the other 10% of the plasma Cu
but binds the metal lers tightly than does





cernloplasim .
Carlo plasim rchibits a Cu- depamadant
oxidase activity,
but its physiologic
significance has not been clarified.
The amt. of cernlo plasim is ↓ed in liner
disease.

5. 1- Antitrypsin(
proteases)





I Amti

It inhibits trypsin, elestsise and certain
other proteases by forming complexes
with their.
A deficiency of this protein has a role in
certain cases of emphysema.
When the amt. Of 1- antitrypsin is
deficient and poly mrerphomvclear WBC
↑se in the lung e.g. in pneumonia the
affected in dirndl lacks a comter check
to proteolytic damage of the lung by





Proteases smh as elastase .
Active elastase +
1- AT → inactive
elastase :
1- AT complex → no
proteolysis of lung → no tusue damage.
Active elastase + ↓ or no
1- AT →
active elastase → proteolysis of lung →
tusue damage.

6. Immunoglobulins


The plasma cells derived from B cells
synthesize circulating immunoglobulins
called antibodies.
Plasma cells are
specialsied cells of B lineage that
synthesize and secrete immunoglobulins
X. the plasma in response to exposure
to uaricty of antigens / Immunogen.

St. of lmmunoglobulins.






Am immunoglobulin mol. Consists of 2
identical light chains (L) and 2 heavy (H)
chains and are linked together via
disulfide linked.
Each chain can be ÷ed X 2 sp. Domains
or
regions having specific st. and
function.
Each light chain consists of a variable
(VL) and a constant (CL) region.







and is towards carboxyl terminal.
Where as amino terminal half is variable
region of the light chain.
Each heavy chain consists of a variable
region (VH) and a constant region i.e
÷ed x 3 domains i.e CH1, CH2. CH3.
VH is ¼ of the heavy (H) chain while the
other ¾ of heavy chain are ÷ed x
regions i.e CH1, CH2, CH3.
CH2 domain contains the complement –
binding site and CH3 domain contains a

a site that attaches to receptors on
nentroplils and macrophages.
 Antigen anti body binding site formed
by hyper variable region of both the
light heavy chains.
 immunoglobulin mol. is Y – shaped
and chains are linked by disulfide
bonds.
 Each immunoglobulin has 2 antigen
binding figments, (FAB) and one
ceystallizable fagmant (Fc).





The site on the antigen to which an anti
body binds is temed as epitope or
antigenic detriment.
The region b/w CH1 and CH2 – hinge
region .

S
┘

S

│

S
┘

▐

sCO
O
H

S

│

-s-

S

┌
-s-sS
-s-s│
▐ ▐
S
/
└
CHO
┌
region
S
│
S
└
COOH
COOH

▐▐
│

Variable site with
Hypemainable
Region

Hinge region

Complement
Binding region

STRUCTURE OF IMMUNOGLOBULIN

Constant region
Of heavy chain

│

S

he
av
y
NH cha
in
2

┐

┐

g
bin

NH
2

om

▐▐
│▐

│

Crystallizable
Fragment
FC

yc

H.
Ch
ai
n

d
bo
ti .
An tes
Si

8
10

Ig. Major Functions.






Ig G :- main anti body in zndry response.
Makes bacteria easier for phagocytosis
x killing and neutralizes bacterial taxis
and vines . Crosses the placenta.
Ig A :- secretary Ig A perverts
attachment of bacteria and vises to
mucous membranes.
Ig M:- produced in prmiay response to
an antigun faces complement.

7.






2 Macroglobulin

Large plasma glycoprotein.
Homo tetramer.
Zn transporting function.
Synthesized by monocytes, hepatscytes
and astrocyes.
Anti protease action,

PROTEINS

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PROTEINS