Insulin Structure

Insulin is composed of 51 amino acids arranged in two polypeptide chains, designated A (21 amino acids) and B, which are linked together by two disulfide bonds (Fig. 1 A). The insulin molecule also contains an intramolecular disulfide bond between amino acid residues of the A chain.
[Note: Insulin was the first peptide for which the primary structure was determined and the first therapeutic molecule made by recombinant DNA technology .]

Figure 1:  A. Structure of insulin. B. Formation of human insulin from preproinsulin. S-S = disulfide bond.