Made by Ayman M.Hany

1. AMINO ACIDS OF
BIOLOGICAL
IMPORTANCE
MADE BY
AYMAN M.HANY

2. AMINO ACIDS

3. AMINO ACIDS
• AMINO ACIDS ARE
ORGANIC ACIDS,
WHICH HAVE ONE OR
MORE SUBSTITUTED
AMINO GROUP (NH2).

4. AMINO ACIDS

5. AMINO ACIDS

6. AMINO ACIDS

7. AMINO ACIDS

8. AMINO ACIDS

9. AMINO ACIDS

10. AMINO ACIDS

11. AMINO ACIDS

12. AMINO ACIDS

13. • Heterocyclic amino acids are those containing rings other
than phenyl ring and they include tryptophan, histidine,
proline and hydroxyproline.
• Aromatic amino acids are those containing aromatic ring
and they include phenylalanine,tyrosine,tryptophan.

14. Hydroxyproline and
hydroxylysine :are
formed by hydroxylation
of proline and lysine
respectively after the
synthesis of the protein.
Selenocysteine: is considered the
twenty first amino acid but it is
uncommon in proteins. It contains
selenium (se) in place of sulfur (S)

15. CLASSIFICATION OF AMINO ACIDS
• Amino acids can be classified into:
I. - chemical classification: according to their chemical structure.
II. - Polar or non-polar: according to the polarity of the side chain.
III. - Nutritional classification: according to their nutritional importance.
IV. - Metabolic classification: according to their metabolic fate.

17. CLASSIFICATION OF AMINO ACIDS ACCORDING TO
POLARITY OF SIDE CHAIN (R-GROUP)
Un charged
polar
Charged

18. NUTRITIONAL CLASSIFICATION OF AMINO
ACIDS
Essentia
l
Semi

19. Proteins that contain all the
essential amino acids are of high
biological value, e.g. Milk and egg
proteins. Proteins that are deficient
in one or more of the essential
amino acids are of low biological
value, e.g. Zein of maize (deficient
in tryptophan).

20. METABOLIC CLASSIFICATION OF AMINO
ACIDS
I-pure ketogenic amino acids:
1. Leucine
2. Lysine.
II-glucogenic and ketogenic (mixed) amino acids:
1. Phenylalanine
2. Tyrosine
3. Tryptophan
4. Isoleucine.
III-pure glucogenic amino acids:
all amino acids except the members of the other two groups.

21. I- AMPHOTERIC PROPERTY
• Amino acids can react both with acids and bases, so they
are ampholytes.
• In acidic medium: they are positively charged (R-
NH3+).
• In alkaline medium: they are negatively charged (R-
COO-).
• At iso electric point (IEP): they form dipolar ions
(zwitterions) which are at pH 6.02 for all monoamino-
monocarboxylic amino acids. In this form, the amino
acid cannot migrate in electric field.
• So, amino acids are present in three forms according to
the pH Of the solution and the uncharged form is not
present at any pH.

22. II- PEPTIDE BOND FORMATION
• Dipeptide is formed by
condensation of the carboxylic
group of one amino acid with
the amino group of a second
amino acid (peptide bond
formation).Proteins are formed
of many amino acids linked
together by peptide bonds

23. PROTEINS OF BIOLOGICAL
IMPORTANCE

24. DEFINITIONS
• Oligopeptides contain from 2 to 10 amino acids
• Polypeptides contain from 11 to 49 amino acids
• Protein molecule is formed of 50 or more amino acids.
• The molecular weight of proteins ranges from 5000 to
several millions.

25. BIOLOGICAL IMPORTANCE AND FUNCTIONS
OF PROTEINS:
1) provide the body with essential amino acids, nitrogen and
sulfur.
2) Enzymes are mainly protein in nature.
3) Many hormones are peptides or protein in nature (e.g.
Glucagon and insulin).

26. BIOLOGICAL IMPORTANCE AND FUNCTIONS
OF PROTEINS:
4) The ANTIBODIES (immunoglobulins) which play an
important role in the body's defensive mechanisms are protein
in nature.
5) Hemoglobin is a chromoprotein. It carries O2 from the lung
to tissues.

27. BIOLOGICAL IMPORTANCE AND FUNCTIONS
OF PROTEINS:
6) Plasma proteins are responsible for most effective osmotic pressure of the
blood. This osmotic pressure plays a central role in many processes e.g Water
distribution and urine formation.
7) Plasma proteins help the transport of many substances in the blood e.g. Lipids
forming lipoprotein complexes, hormones (e.g. Thyroid hormones) and minerals
(e.g. Calcium, iron and copper).
8) They form very important components of different types of cell membranes e.g.
Receptors and transporters.

28. STRUCTURE OF PROTEINS
I- Primary structure:
II- Secondary structure:
1. α-Helix
2. β-pleated sheet
3. Loop regions
4. Β bends
5. Disordered regions.
III- Tertiary structure:
IV- Quaternary structure:

29. I- Primary structure:
1. The primary structure refers to the
amino acid sequence of the
polypeptide chain.
2. The primary structure is held
together by peptide bonds,
3. The amino acid sequence of any
protein is specific to that protein.

30. I- Primary structure:
4. The polypeptide chain starts on the left side
by amino acid number 1, which contains a
free terminal amino group and termed N-
terminus amino acid. On the right side, at
the end, the polypeptide chain contains an
amino acid with a free terminal carboxylic
group and termed C-terminus amino acid.

31. I- Primary structure:
5. The synthesis of the polypeptide chain starts from
the N-terminus end toward the C-terminus.
6. The change of a single amino acid in the linear
order of the polypeptide chain may lead to
profound physiologic effects.
7. The genetic information present in DNA controls
the primary structure of proteins, which
determines the secondary and tertiary structures
that are essential for functions of proteins.

32. II- Secondary structure:
1. α-Helix
2. β-pleated sheet
3. Loop regions
4. Β bends
5. Disordered regions.

33. II- Secondary structure:
1. α-Helix
1. In α-Helix polypeptide, the backbone is tightly
coiled around the long axis of the molecule to form a
coil. The -helix is stabilized by intra-chain
hydrogen bonds, which are formed between NH
groups and C=O groups. Each peptide bond
participates in the hydrogen bonding. This gives
maximum stability to α-Helix .
2. The R-groups of amino acids project outwards of
the helix.

34. II- Secondary structure:
1. α-Helix
3. The R groups of some amino acids
can disrupt the α-helical structure e.g.
Proline, histidine, lysine,and glutamic
acid, due to formation of other types
of bonds as ionic bonds or their ring
structures disturb the helical
formation.

35. II- Secondary structure:
2.β-pleated sheet
1. The polypeptide chain is fully extended and the
chains line up side by side to form sheet and the side
chains are above or below the plane of the sheet.
From 2 to 5, adjacent strands of polypeptides may
combine and form these structures.
2. When the adjacent polypeptide chains run in same
direction (N to C terminus), the structure is termed as
parallel β-pleated sheet. When the adjacent
polypeptide chains run in opposite direction, the
structure is termed as anti-parallel β-pleated sheet.

36. II- Secondary structure:
2.β-pleated sheet
3. The β-pleated sheet is stabilized by inter-
chain hydrogen bonds.
N.B. β-pleated sheets may form between
different regions of the same polypeptide
chain, and will be stabilized by intra-chain
hydrogen bonds.

37. III- TERTIARY STRUCTURE

38. IV- QUATERNARY STRUCTURE

39. STRUCTURE OF PROTEINS

40. Chaperones
• Proteins must fold into defined three-dimensional structures to gain functional
activity.
• In the cellular environment, newly synthesized proteins are at great risk of
aberrant folding and aggregation, potentially forming toxic species.
• Chaperones (group of molecular proteins) use different mechanisms to promote
efficient protein folding and prevent aggregation.
• An age-related decline in chaperones allows the manifestation of various protein-
aggregation diseases, including alzheimer's disease and parkinson's disease.

41. DENATURATION OF PROTEINS
• Denaturation is a specific property of proteins.
• It is due to the rupture of chemical bonds that stabilize the
secondary, tertiary and quaternary structure of the protein.
• It may be reversible or irreversible and may result in protein
coagulation e.g. Albumin coagulation by heat (due to formation of
disulfide cross linkage).

42. FACTORS THAT PRODUCE DENATURATION :
1- physical agents:
1. Heat
2. Mechanical agitation
3. Sonication
4. Ultraviolet irradiation
5. X-ray
2 - chemical agents:
1. Acids
2. Alkalis
3. Alcohols
4. Urea
5. Salts of heavy metals like pb2+, ag2+,
cu2+

43. EFFECTS OF DENATURATION ON PROTEINS
1. Loss of the secondary, tertiary and quaternary structure of proteins.
2. Loss of biologic activity e.g. Inactivation of enzymes.
3. Loss of antigenic property i.e. Injection of denatured protein cannot induce antibody
formation within the body, in the contrary to the action of native proteins.
4. Increased viscosity.
5. Increased digestibility by proteolytic enzymes due to exposure of peptide bonds.
6. Decreased solubility due to exposure of nonpolar hydrophobic groups.

44. CONFORMATIONAL CLASSIFICATION OF
PROTEINS
• I- fibrous proteins: they consist of polypeptide chains that are arranged in a
parallel form along a single axis to yield long fibers or sheets.
a) Collagen
b) Elastin
c) Keratin.
• II- globular proteins: they are tightly folded into compact spherical or globular
shapes. E.g. Most of enzymes, hemoglobin, myoglobin, many hormones,
immunoglobulins and plasma proteins.