Chemistry of amino acids

1. Chemistry of aminoacids

2. Amino Acids
• All the major structural and functional aspects
of the body are carried out by protein
molecules.
• All proteins are polymers of amino acids.
• Proteins are composed of a number of amino
acids linked by peptide bonds.

3. PEPTIDE BOND

4. PEPTIDE BOND FORMATION
• Alpha carboxyl group of one amino acid
reacts with alpha amino group of another
amino acid to form a peptide bond or CO-NH
bridge.
• Proteins are made by polymers of amino acids
through peptide bonds.

5. General structure of amino acids
• Most of the amino acids (except proline) are
alpha amino acids, which means that the
amino group is attached to the same carbon
atom to which the carboxyl group is
attached.

6. • The α-carbon atom binds to a side chain
represented by R which is different for each of
the 20 aminoacids found in proteins

7. General structure of aminoacid

8. CLASSIFICATION OF AMINO ACIDS
• Classification based on Structure:
• Amino acids with aliphatic side chains :
• simple amino acids- glycine, alanine.
• Branched chain amino acids: Valine, Leucine,
Isoleucine

9. Simple amino acids

10. Branched chain amino acids

11. • Hydroxyl group containing amino acids :
• Serine, threonine are hydroxyl group
containing amino acids.

12. • Sulphur containing amino acids :
• Cysteine with sulfhydryl group and
methionine with thioether group.

13. Cysteine and methionine

14. • Amino acids with amide group: Asparagine,
Glutamine

15. • Acidic amino acids: Aspartic acid, Glutamic
acid

16. • basic amino acids: Lysine, Arginine

17. • Aromatic amino acids : Phenylalanine,
tyrosine

18. • Heterocyclic amino acids: Tryptophan ,
Histidine

19. Proline

20. Nutritional classification of amino acids :
• Essential or Indispensable
• The amino acids which cannot be synthesized
by the body and, therefore, need to be
supplied through the diet are called essential
amino acids.
• They are required for proper growth and
maintenance of the individual.

21. Pneumonic for essential aminoacids

22. • Partially essential or Semi-essential:
• Histidine and arginine are semi-indispensable
amino acids.
• Growing children require them in food.
• But they are not essential for the adult
individual.

23. • Non-essential or dispensable amino acids :
• The remaining 10 amino acids are non-
essential, because their carbon skeleton can
be synthesized by the body.
• These are- glycine, alanine, serine, cysteine,
aspartate,asparagine, glutamate, glutamine,
tyrosine and proline.

24. • Ampholyte and Iso-electric Point:
• Amino acids can exist as ampholytes or
zwitterions (German word "zwitter" = hybrid)
• Zwitter ion (or dipolar ion) is a hybrid
molecule containing positive and negative
ionic groups.

25. • In strongly acidic pH (low pH), the amino acid
is positively charged (cation),while in strongly
alkaline pH (high pH), it is negatively charged(
anion).

26. Significance of iso-electric pH(pI)
• The pH at which the molecule carries no net
charge is known as iso-electric point or
isoelectric pH (pI).
• At this pH, a molecule exists as a zwitterion or
dipolar ion and carries no net charge.
• Thus, the molecule is electrically neutral .

27. • Therefore at isoelectric point, there is no
mobility in an electrical field.
• Solubility and buffering capacity will be
minimum at iso-electric pH.

28. Ampholyte and Iso-electric Point

29. Ionic forms of aminoacids

30. • Chemical properties:
• Reactions due to Carboxyl Group:
• Decarboxylation: The amino acids will
undergo alpha decarboxylation to form the
corresponding amine.

31. Decarboxylation

33. • Reactions Due to Amino Group:
• Transamination: The alpha amino group of
amino acid can be transferred to alpha keto
acid to form the corresponding new amino
acid and alpha keto acid.
• This is an important reaction in the body for
the inter-conversion of amino acids

34. • This transfer of amino groups from one carbon
skeleton to another is catalyzed by a family of
enzymes called aminotransferases.
• The two most important aminotransferase
reactions are catalyzed by alanine
aminotransferase (ALT) and aspartate
aminotransferase (AST).

35. • The enzyme alanine aminotransferase (ALT)
catalyzes the transfer of the amino group of
alanine to α-ketoglutarate, resulting in the
formation of pyruvate and glutamate.
• The reaction is readily reversible.

36. Transamination

37. Transamination

38. Biuret test
• Procedure:
• To 2 mL protein solution, add 2 ml of 5%
NaOH and mix well. Add 2-3 drops of 1%
cuso4 solution and mix well.
• Observation:
• A Violet coloured complex is formed.

39. • Principle:
• Cupric ions in an alkaline medium form a
violet colour with peptide bond nitrogen.
• This needs a minimum of two peptide bonds,
and so individual amino acids and di-peptides
will not answer this test.

40. Biuret test