Amino acid -Classification of amino acid, Properties, peptides-Types and biological importance

1. Shri Shankaracharya Mahavidyalaya, Junwani ,
Bhilai
Dr. Sonia Bajaj
(Head of Department)
Amino Acid and Peptide

2. SYNOPSIS
• Introduction
• Definition
• Functions of Amino acids
• General Structure of Amino acids
• Classification of Amino acids
• Structure of Amino acids
• Properties of Amino acids
• Peptides
• References

3. INTRODUCTION
 Amino Acids are the building units of proteins. Proteins are polymers of
amino acids linked together by what is called “ Peptide bond” (see latter).
 There are about 300 amino acids occur in nature, only 20 of them occur in
proteins.
 The key element of amino acids are carbon (C), hydrogen (H), Oxygen (O)
and nitrogen (N).

4. DEFINITION
• Amino acids are group of organic compounds containing two functional groups
i.e. amino and carboxyl group.
• The amino group (NH2) is basic while the carboxyl group (COOH) is acidic in
nature.

5. GENERAL STRUCTURE OF AMINO ACID

6. CLASSIFICATION OF AMINO ACIDS
Classification
of Amino
acids
Based on
Structure
Based on
Polarity
Based on
Metabolic
Rates
Based on
Nutritional
classification

7. Based on Structure

11. BASED ON POLARITY

12. CLASSIFICATION BASED ON METABOLIC
RATE
• According to metabolic and degradation products of amino acids they may be :
Glucogenic Amino acids
Ketogenic amino acids
Mixed Glucogenic and ketogenic Amino acid

13. BASED ON NUTRITIONAL
CLASSIFICATION

14. PROPERTIES OF AMINO ACIDS
PHYSICAL PROPERTIES
1. Solubility
2. Melting Point
3. Taste
4. Optical Isomerism

15. • CHEMICAL PROPERTIES
1. Amino acids forms salts ( COONa) with bases and esters ( COOR’) with alcohols.
2. Decarboxylation
3. Reaction with Ammonia

16. 4. Reaction with Ninhydrin
5. Transamination

17. 6. Oxidative deamination

18. AMINO ACIDS AS DRUGS
• D-penicillamine (D-dimethylglycine), a metabolite of penicillin is employed in the
chelation therapy of Wilson disease. This is possible since D-penicillinamine can
effectively chelate copper.
• N-acetylcysteine is used in cystic fibrosis and chronic renal insufficiency as it can
function as an antioxidant.

19. FUNCTIONS
• Main function of amino acid is to serve building block of protein.
• Essential for proper functioning of our body.
• Circulatory function- Blood clotting control through protein such as fibrinogen.
• Structural function- Skeleton, muscle. skin and generally all tissues of body are made
up of proteins.
• Motion function- Amino acid make a locomotory movement through muscle fibres.
• Hormonal function- All hormones are formed by amino acid.
• Transport function- Albumin is very abundant protein in the blood.

20. PEPTIDE:
Peptide (peptide bond) is amide linkage formed by the reaction between α-carboxyl group of one
amino acid and α-amino group of another amino acid with the elimination of water molecule.
Peptide bond has partial double bond character so it is shorter than single bond and longer than
double bond.
Peptide bond is rigid and planner.
The partial double bond character of peptide bond, prevent free rotation of polypeptide chain.
The peptide bond is ‘trans’ It never occurs in ‘cis’ configuration due to steric hindrance.
-COO and -NH group of peptide bond does not ionize but is polar, so it can form hydrogen bond
during formation of secondary structure of proteins.

21. TYPES OF PEPTIDES
1. Dipeptides:
Compound formed when two amino acids linked by 1 peptide bond.
Examples:
Carnosine ( β-alanyl-L-histidine)
Anserine (β-alanyl-N-methylhistidine)
Aspartame (Asparagine-phenylalanine)
2. Tripeptides
Compound formed when three amino acids linked by 2 peptide bond.
Examples;
Glutathione ( Glutamyl-cystinyl-glycine)
Opthalmic acid (L-γ-Glutamyl-α-L-amino butyrl-glycine)
3. Oligopeptides
Compound formed when more than 2 and less than 20 amino acids are linked by peptide bonds.
Examples;
Tetrapeptide; Tulfsin ( thrionine-lysine-proline-Arginine)
Endomorphin-1 ( Tyrosine-proline-tryptophan-phenylalanine)
Amanitin ( Decapeptide)
Netropsin
4. Polypeptides
Compound formed when more than 20 amino acids are linked by peptide bond.
Examples:
Insulin ,Growth hormone

22. Functions of peptides:
i. Precursor of protein: Peptides are precursor of protein.
ii. As alkaloids: Peptides are also the constituents of alkaloids (Alkaloids are group of
secondary metabolites such as Nicotin, Caffeine, Terpentine, Ergotamine etc).
iii. As Antimicrobial agent: Peptides possess antibacterial properties. Secondary metabolites
of bacteria and fungi have antimicrobial activity. Eg. Penicillin G ( valine-cystein-phenylacetic
acid).
iv. As Hormones: Peptides acts as hormones eg. Insulin, Somatostatin, vasopressin etc.
v. Peptides also acts as growth factors. Eg. Ascorbic acid (vit. C).
vi. As anti-oxidant: Peptide functions as anti-oxidant. They scavenge free radicals. Eg.
Carnosine.
vii. Clinical diagnosis: hyper secretion of peptide in urine is indicator for mental state of
disturbance like depression, schizophrenia etc.
viii. As structural component: peptides form long chains creating structural protein which
provides support to body. Eg. Keratin, collagen

23. BIOLOGICAL FUNCTION OF PEPTIDES

24. REFERENCE
• Lehninger Principles of Biochemistry by David L. Nelson and Michael M. Cox.
• Microbiology by Powar and Daginawala.
• Biochemistry by U. Satyanarayana.
• Biochemistry by J.L. Jain.