Read the given passage and answer the following questions:
Managing diabetes is possible by administering insulin periodically. Insulin used for diabetes was earlier extracted from pancreas of slaughtered cattle and pigs. However, this insulin caused some people to develop allergies and other types of reactions. In mammals, including humans, insulin is synthesised as a prohormone and is later converted to insulin. Insulin consists of two short polypeptide chains: chain A and chain B, that are linked together by disulphide bridges.
How were the A and B chains of human insulin combined to form the mature hormone?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → By creating disulfide bonds
The passage states that insulin consists of two short polypeptide chains, chain A and chain B, “that are linked together by disulphide bridges”.
A disulphide bridge is a bond between two sulphur atoms, one on each chain. In the method used to make human insulin, the two chains were produced separately and then joined by creating these bonds to form the mature hormone.
Option (1) By adding a C peptide — Incorrect. The C peptide is the extra stretch of pro-insulin. It is removed during maturation; it is not added to join the chains.
Option (2) By forming peptide bonds — Incorrect. Peptide bonds join the amino acids within each chain. The two chains are held to each other by disulphide bonds.
Option (3) By using a special enzyme — Incorrect. No special joining enzyme is named. The chains were combined by creating disulphide bonds between them.
Option (4) By creating disulfide bonds — Correct. Chains A and B are joined by disulphide bonds, which hold the two chains together in mature insulin.