proteins are one of the most abundant organic molecules in living systems and have the most diverse range of functions of all macromolecules. Proteins may be structural, regulatory, contractile, or protective; they may serve in transport, storage, or membranes; or they may be toxins or enzymes. Each cell in a living system may contain thousands of different proteins, each with a unique function. Their structures, like their functions, vary greatly. They are all, however, polymers of alpha amino acids, arranged in a linear sequence and connected together by covalent bonds. Alpha Amino Acid Structure The major building block of proteins are called alpha (α) amino acids. As their name implies they contain a carboxylic acid functional group and an amine functional group. The alpha designation is used to indicate that these two functional groups are separated from one another by one carbon group. In addition to the amine and the carboxylic acid, the alpha carbon is also attached to a hydrogen and one additional group that can vary in size and length. In the diagram below, this group is designated as an R-group. Within living organisms there are 20 amino acids used as protein building blocks. They differ from one another only at the R-group position.

2. Proteins are the most abundant biological
molecules present in the cell.
Proteins have a large number of functions including:
structural and functional.

3. 1- Catalytic Function
Enzymes catalyze chemical reactions converting a
substrate to a product .
2-Transport function
Hemoglobin and myoglobin transport oxygen in
blood and muscles respectively.
Transferrin transports iron in blood.

4. 3- Contractile function
Myosin and actin proteins are the major
components of muscles.
4- Protective function
The immunoglobulins (antibodies) are proteins
produced by plasma cells to act against
different bacteria and viruses that invade the
body

5. 5- Regulatory function
Many hormones and hormone receptors are
proteins.
6- Structural function
collagen and elastin which form the matrix
of bones and ligaments and provide
structural strength and elasticity to organs
and vascular system.
Keratin is present in hair and other
epidermal tissues .

6. •In nature: > 300 different A.A.
•In mammalian proteins, there are 20 common
A.A.
•Selenocysteine is the 21st A. A. is found in many
proteins.

7. All proteins are synthesized from 20
amino acids .
polymerization of amino acids into a
specific linear sequence characteristic
for each protein is called polypeptide
chain.

8. Each amino acid (AA) has a carboxyl group
COOH and an amino group NH2 bonded to the
same carbon.
They have the following general structure:
COOH
|
NH2 C H
|
R
Amino acids differ from each other in their side
chains or R group

9. • These amino acids are :
Glycine, Alanine , Valine , Leucine,
Isoleucine, Proline, Serine , Threonine,
Cysteine , Methionine, Aspartic , glutamic,
Lysine , Arginine, Aspargine, Glutamin,
Histidine , Phenylalanine, Tyrosine and
Tryptophan.

10. Classification of AAs
Chemical : According to the
structure of the side chain ‘R
group’.
Nutritional: Whether the A.A can
be synthesized in the body or not.
Metabolic: according to the fate of
the A.A inside the body.

11. • Classification of Amino Acids:
Chemical classification
Aromatic A A ; Phenylalanine, tyrosine
and tryptophan.(have a benzene ring)
Cyclic A A ; histidine and proline.
Aliphatic A A; the rest of A A.

12. Nutritional classification
Non Essential A A : They can be
synthesized inside the body and do not
have to be taken in diet.
Essential A A: They are 10 AA ,can not be
synthesized in the body and so they
must be supplied in diet .
Arginine Histidine Isoleucine
Leucine Therionine Lysine
Methionine Phenylalanine
Tryptophan Valine

13. Arginine is considered as semi-essential amino
acid especially in growing children as it is formed
in body but in insufficient amounts

14. Proteins are classified according to their
contents of essential AA into:
1- Proteins of high biological value
These are animal proteins which contain
all essential AA needed by the body.
2-Proteins of low biological value
Vegetable proteins lack one or more
essential AA .

15. Metabolic classification
(1)Pure ketogenic: can give ketone bodies
inside the body. Include leucine and
lysine
(2) Pure glucogenic: can give glucose
inside the body. Include the other amino
acids.
(3) Mixed glucogenic and ketogenic.
Include phenylalanine, tyrosine,
tryptophan, and isoleucine.

16. Peptides and proteins are polymers of
amino acids.
Chemically this polymerization is a
dehydration reaction requiring energy.
The carboxyl group of an AA forms a
peptide bond with the amino group of the
next AA with removal of one molecule of
water producing a dipeptide.

17. R1 R2
| |
NH2 – C H – COOH + NH2 – C H – COOH
AA 1 AA 2
H2O
The condensation reaction requires energy
R1 H R2
| | |
NH2 – C H – C ----- N –C H – COOH
||
O
A dipeptide

18. Orders "levels" of protein structure”
‘Four organization levels

19. Primary structure of
proteins:
•Is the linear
sequence ‘order’ of
A.A ‘joined by
peptide bonds’
•Abnormal A.A.
sequence results
in improper
folding and loss
of normal
function as in
many genetic
diseases.

20. Secondary structure ‘arrangement:
•Include α- helix, β-Sheet,
•α– helix:
•The most common type of helices. It is tightly
packed spiral structure.

21. β- pleated sheet:
•It has pleated ‘’ zigzag like ‘’ outer surface
and visualized as broad arrows.

22. Tertiary structure of proteins:
Is the three-dimensional structure of a protein.

23. Quaternary structure:
Is the arrangement of the subunits of a proteins
consisting of two or more polypeptide chains
A protein may be
monomeric :
consists of a single polypeptide chain
Or
• polymeric :
consists of more than one polypeptide chain

24. Quaternary structure:

25. Each protein is characterized by its final shape
which is maintained by a group of bonds.
Denaturation of the protein is defined as:
a change in its physical, chemical or biological
properties .
Denatured protein looses its secondary , tertiary
and /or quaternary structure .
Primary structure is not affected by Denaturation .

26. Denaturating factors which include :
a) Physical factors as
- high temperature
- vigorous shaking
- high pressure
- U.V and X-ray irradiation.
b) Chemical reagents as
- strong acids and bases
c) Biological agents as
- enzymes