Proteins lecture

1. PROTEINS
Mahpara Gondal
Rashid Latif College of Pharmacy

2. Objective
O Peptides
O Importance of peptides
O Classify proteins.
• Based on size and shape,
• Based on functions,

3. Peptide Linkage and
Peptides
O The –COOH group of one amino acid can
be joined to
O the –NH2 group of another by a covalent
bond called as peptide bond.
O In the process of formation of a peptide
bond a molecule of water is eliminated

4. Peptide linkage
O .

5. Cont…
O When two aminoacids are joined together
by one peptide bond, such a structure is
called as dipeptide.
O third amino acid can form a second
peptide bond through its free –COOH end
and is called tripeptide

6. Cont…
O ,

7. Cyclic peptides
O Cyclic peptides differ from normal peptide
due to their ring structure.
O Gramicidin S is a
cyclodecapeptide,constructed as two
identical pentapeptides joined head to tail,
formally written as cyclo(-Val-Orn-Leu-D-
Phe-Pro-)2. That is to say, it forms a ring
structure composed of five different amino
acids, each one used twice within the
structure.

8. Cont…
O .

9. .
O .

10. Toxic peptides
O Some peptides act as toxin.
O Alpha amanitin is a bicyclic octapeptide
present in many mushrooms and is
extremly toxic to human being.
O They immadietly cause pain in GIT,
Nausea, vomiting, diarrheoa.
O Death may occur within a week due to
impairment of liver and kidney functions.

11. Importance of peptides
O Glutathione: This is a tripeptide
consisting of glutamic acid, cysteine
and glycine. By virtue of easy
dehydrogenatio it gets converted to
disulphide form and function in oxidation-
reduction systems.
O Bradykinin: Bradykinin (9 amino acids) or
Kallidin I and Kallidin II (10 amino acids)
have relaxant effects on smooth muscle.

12. Cont…
O Antibiotics: Penicillin, gramicidin,
polymyxins, bacitracins, actinomycin,
chloramphenicol are all peptides which act
as antibiotics.
O Gastrin, Secretin and Pancreozymin:
Are gastrointestinal peptides which act as
hormones which stimulate secretion of
bile and other enzymes of digestive juices.

13. Cont…
O Angiotensins: The enzyme Renin is released
from kidneys and acts on globulin fraction of
plasma to release a peptide Angiotensin I
(10 amino acids) which has only a slight
effect on blood pressure, Angiotensin I is then
converted to Angiotensin II by splitting off
two amino acids which has eight amino acid,
has greater effect on BP.
O Removal of one residue aspartic acid from
Angiotensin II results in formation of
Angiotensin III (7 amino acids) which plays
role in pathology of hypertension.

14. Proteins
O Proteins are most complex biological
molecule composed of a large number of
amino acids residue arranged in one or
more polypepetide chain.

15. Classification
O Based upon their shape
O 1. Globular proteins
O 2. fibrous proteins

16. Fibrous proteins
O When the polypeptide chains are
extended along one axis, it is called a
fibrous protein.
O Examples: α-keratin and b- keratin from
hair, collagen and elastin from bones.

17. Globular proteins
O Polypeptide chains of these proteins are
folded into compact globular (Spherical
shape).
O For example: Myoglobin, haemoglobin,
ribonuclease, chymotrypsin.

19. Cont…
On the basis of functional properties:
O The second way of classifying proteins
makes use of their functional properties.
O 1. Defence proteins: Immunoglobulins
involved in defence mechanism. Other
example gamma globulin.

20. Cont…
O 2. Contractile proteins: Proteins of skeletal
muscle involved in muscle contraction and
relaxation.
Example: Actin and myosin
O 3. Respiratory proteins: Involved in the
functio of
respiration, like haemoglobin, myoglobin,
cytochromes.
O 4. Structural proteins: Involved to the
structure of tissue like Proteins of skin,
cartilage, nail.

21. Cont…
5. Regulatory Proteins:
Act as hormones like insulin , growth
hormone
6. Catalytic Proteins:
Involved in biochemical reactions.
Like lipases, proteases.

22. Cont…
7. Transport Proteins:
These proteins carry substances in the
blood.
Example: Hb carries oxygen.
8.Genetic Proteins:
These proteins are found in combination
with nucleic acid.
Example: Histones and Protamines

23. cont…
9. Storage Proteins
Store proteins for nutritional purposes.
Examples:
OVO albumin of egg
White casein of milk
Gluten and gliadin of wheat
Zein in maize