Define Amino Acid with Classification and Chemical Structure

Amino acids are the main structural units of protein. Amino acids are formed by the replacement of hydrogens with one to many amino groups (-NH2) in any organic acids. Thus an amino acid contains at least one amino acid group (-NH2) and one carboxylic acid group (-COOH).

Chemical structure: The molecular formula of amino acid is RCH-NH2-COOH.

Thus, on the basis of the variation of ‘R’ amino acids may be of different types. For a simple amino acid glycine, ‘R’ is simply a hydrogen atom.


Classification of amino acid: There are twenty different types of amino acids in plant and animal bodies. These twenty different type’s amino acids are classified into following divisions.

(1) A combination of one amino group and one carboxylic acid group.

  1. Glycine ii. Alanine iii. Valine iv. Leucine v. lsoleucine

(2) A combination of one amino group and two carboxylic acid groups.

  1. Glutamic acid ii. Aspertic acid

(3) A combination of two amino groups and two carboxyl groups

  1. Arginine ii. Lysine iii. Hydroxylycine

(4) Associted with hydroxyl group.

  1. Threonine ii. Serino.

(5) Associated with sulphur

  1. Cytine ii. Methionine

(6) Aromatic:

  1. Phenylalamine ii. Tyrosine

(7) Heterocyclic:

  1. Tryptophan ii. Proline iii. Hydroxy proline

Functions of protein: The main function of amino acid is to synthesise protein.