Amino Acids

Amino acids are compounds containing carbon, hydrogen, oxygen and nitrogen. They serve mainly as monomers (building blocks) of proteins.

An amino acid is represented by a general empirical formula R.CH.NH₂. COOH. Each amino acid has at least an amino (NH₂) group and a carboxyl (COOH) group. R is the function group, which varies from one amino acid to another.

There are about 20 amino acids that form the constituents of cell proteins. These are called protein amino acids. Many amino acids found in cells do not take part in the formation of proteins. These are called non-protein amino acids.

Amino acids are recognised into three groups based on their reaction in solution, namely

Acidic Amino Acids

These have two carboxyl groups and one amino group. The free carboxyl group is acidic in nature. For example, aspartic acid and glutamic acid.

Basic Amino Acids

These have two amino groups and one carboxyl group. The free amino group is basic in nature. For example, Lysine and Arginine.

Neutral Amino Acids

These have one amino and one carboxyl group. For example, alanine, glycine.

fig.13.13 - Structural Formula of Amino Acids

Amino acids can become linked with one another by a linkage called peptide linkage. The amino group of one amino acid becomes linked with the carboxyl group of another amino acid, with the elimination of a molecule of water. The bond that is established in this linkage is called peptide bond. This linkage takes place during the synthesis of proteins in a cell.

Amino acids are also involved in the synthesis of various other biologically significant compounds. Tyrosine, for example, is involved in the synthesis of thyroxine and adrenaline hormones.

Amino acids can get converted into sugars by losing the amino group. Some amino acids may lose the carboxyl group to form biologically active amines such as histamine.