The A and B polypeptides chains in insulin are linked together by which bond?

Disulphide

The correct answer is Option (2) → Disulphide

Insulin is composed of two short polypeptide chains, chain A and chain B, connected by disulfide bridges. In mammals, including humans, insulin is initially synthesized as a pro-hormone, which includes an additional segment known as the C peptide. During maturation into insulin, this C peptide is removed, and the insulin becomes fully mature and functional.

In 1983, the American pharmaceutical company Eli Lilly successfully created two DNA sequences corresponding to the A and B chains of human insulin. These DNA sequences were inserted into plasmids, which were then introduced into Escherichia coli (E. coli) bacteria. Inside the E. coli cells, the A and B chains of insulin were produced independently as separate protein molecules. After extracting the A and B chains from the bacterial culture, they were combined and linked together through the formation of disulfide bonds, resulting in the creation of fully functional human insulin. This achievement marked a significant milestone in medicine, as it enabled the production of human insulin using recombinant DNA technology, revolutionizing the treatment of diabetes worldwide.