The two polypeptides of human insulin linked together by Covalent bond, Hydrogen bonds, Disulphide bridges, Phosphodiester bond?

Insulin is composed of two peptide chains referred to as the A chain and B chain. A and B chains are linked together by two disulfide bonds, and an additional disulfide is formed within the A chain. In most species, the A chain consists of 21 amino acids and the B chain of 30 amino acids.