For Medical & Non Medical Students

1. PEPTIDES
&
ITS ROLE IN THE BODY
By
N.Santhosh Kumar
Asst.Professor
Department of Biochemistry
SIMS & RH

2. FORMATION
OF
PEPTIDE BONDS

3. Amino acids containing two functional groups.
Amine group (- NH2)- Basic
Carboxyl group (COOH) - Acidic in nature
R- Side chain is most imp in determining reactivity of amino acids

5. • All the amino acids are held together in a protein by
covalent peptide bonds.
• When the carboxyl group of an amino acid combines with
the amino group (NH2) of another amino acid to form
peptide bond & produces a molecule of water
• Number of amino acids joined by a peptide bond (-CO-
NH-) to form dipeptide, tri, tetra and poly peptides
• Amino acid is read from N -terminus to the C- terminus
end in the protein

6. PEPTIDES

7. PEPTIDES
Peptides are relatively small polymers, having less
than 100 a.a’s
Depending on the no. of a.a’s they are called as di,
tri, tetra peptide and polypeptide.
Many peptides are formed from breakdown of
proteins and have a no. of functions

8. Physiologically
Active
Peptides
Glutathione
Bradykinin
Angiotensin
Vasopressin
Oxytocin
Thyrotropin –releasing
hormone (TRH)

9. Glutathione
(Tripeptide)
Biologically active reducing
agent
Maintains membrane structure
& integrity of RBCs
Protects membranes of RBC
from oxidation agents(H2O2)
Involved in transport of amino
acids through Meister cycle
Involved in the detoxification
process

10. Role of
NADPH & Glutathione
in cells against
free radicals

11. Peptide Biological Importance
Bradykinin
Nano-peptide
- Formed from an
α2-globulin by
proteolytic action
of trypsin
-Contraction of non-vascular smooth
muscle in the bronchus and gut
- Increases vascular permeability
- Involved in the mechanism of pain
Angiotensin
Formed from an α2-
globulin by the
action of renin
- Renin-angiotensin system plays an imp
role in regulation of Blood pressure &
Fluid balance

13. Peptide Biological Importance
TRH
Tripeptide
(Pyroglutamate-His-Pro)
-Released from the hypothalamus
-Acts on the anterior pituitary gland
- Increases the secretion of TSH
Met-enkephalin
Penta-peptide
Tyr-Gly-Gly-Phe-Met
- Synthesed in brain
- Act as a pain reliever
Oxytocin
cyclic nano-peptide
hormone
- Secreted by posterior pituitary gland
- Causes contraction of uterus.
Vasopressin
Nanopeptide
-Antidiuretic hormone (ADH),
- Stimulates kidneys to retain water
- Increase the blood pressure

14. PROPERTIES
OF
PROTEINS

15. Solubility
Proteins forms colloidal solutions instead of true
solution in water, because of huge size of protein
molecule
Smaller molecules more soluble than larger
molecules

16. Osmotic Pressure
In blood plasma- Albumin contributes 75- 80% of
colloidal osmotic pressure
Clinically Imp In Maintaining Blood Volume

17. Every protein in solution, there is a particular pH
(soln is electrically neutral)
Isoelectric pH of protein
At this pH, solubility, buffering capacity, viscosity of
protein is minimum & precipitability is maximum
Ex : PI of pepsin- 1.1, casein is 4.6, Alb is 4.7,
globulin is 6.4
PI of protein molecule do not migrate in an electric field

18. Stability of protein in soln depends on the charge &
hydration of the protein molecules
Neutralize the charge or remove water of hydration will
cause precipitation
Increased protein –protein interaction leads to
molecular aggregation & precipitation
Precipitation Of Protein

19. Factors used for Precipitation of
proteins
Salting out (Precipitated by salts)
Isoelectric pH of protein
Organic solvents
Heavy (+) or (-) ions

20. Denaturation of Protein
 The breaking native structure of protein (mainly rupture of ionic
bond, H-bonds & hydrophobic bond but peptide bonds are not
hydrolysed).

21. Denaturing agents
Physical agents
Heat, UV rays & Ionizing radiations
Chemical agents
Alkalies & certain acid solutions of heavy metals,
eg. Mercury, Lead, Detergents
Organic solvents
Alcohol, Acetone, Urea solution

22. Denaturation of protein leads to.
• Decrease in solubility & increase in precipitability.
• Loss of biological activities
• It is usually irreversible
• Viscosity of denatured protein increases while its surface
tension decreases.
• These proteins are easily digested and cannot be crystallized.

23. Next class
CA&P- 03 Classification and Properties of
Proteins

24. Education = Knowledge
Knowledge = Power
Power = Respect
Respect = Happiness