The primary structure of insulin is described as follows.

Insulin a small protein of molecular weight is made of two polypeptide chains, A chain and B chain joined to each other by two disulphide cross-links.

The A-Chain has 21-amino acids, and the B-Chain has 30-amino acids. The compound also has a quaternary structure in which the two chains are linked between cysteine molecules present at the 7^th position of each chain and between cysteine at 20^th of A chain and 19^th of B chain.

The A chain has a secondary structure with an intra molecular disulphide bond between cysteine molecules at 6^th and 11^th position.