NEET 2021 Zoology Question 160 Solution

Human insulin is synthesized by beta cells of the islets of Langerhans as an inactive pro-hormone (pro-insulin): - Pro-insulin structure: Consists of three polypeptide chains: Chain A (21 amino acids), Chain B (30 amino acids), and an intervening C-peptide (connecting peptide, 31-35 amino acids). - Maturation: Endopeptidases cleave out the C-peptide, leaving mature functional insulin consisting of only the A-chain and B-chain linked together by two interchain disulphide bridges (and one intrachain disulphide bond on Chain A). - Therefore: - Statement (a) is True: C-peptide is absent in mature insulin. - Statement (c) is True: Pro-insulin possesses the extra C-peptide segment. - Statement (d) is True: A-peptide and B-peptide are interconnected by disulphide bonds.

The major challenge in producing insulin using rDNA technology was getting insulin assembled into a mature form without cellular proteolytic processing machinery: - In 1983, the American pharmaceutical company Eli Lilly synthesized two independent DNA sequences corresponding to Chain A and Chain B of human insulin. - They inserted them separately into plasmids of *Escherichia coli*. - Chains A and B were produced separately, extracted, purified, and subsequently combined by creating disulfide bonds chemically *in vitro*. - Consequently, genetically engineered insulin never contains C-peptide. Thus, Statement (b) is False.