Insulin is synthesized by the beta cells of Islets of Langerhans of the pancreas. Insulin is a heterodimeric peptide. It is made up of two chains A and B and contains 21 and 30 amino acids respectively. Both the chains are linked by interchain disulfide bonds.
Insulin is synthesized as a preprohormone consisting of a single polypeptide chain having 109 amino acid residues. A hydrophobic 23 amino acid peptide (Leader sequence) directs the molecule into the cisternae of the rough endoplasmic reticulum (RER) where it is cleaved into proinsulin consisting of 86 amino acids.
Proinsulin is also a single polypeptide chain containing B-chain-connecting peptide (C-chain)-A chain. The proinsulin is transported to the Golgi complex where is undergoes series of proteolytic cleavages to give mature insulin consisting of 51 amino acids and the C-peptide having 35 amino acids. The C peptide has no biological activity. The gene responsible for the production is insulin is located on the short arm of chromosome 11.
