Which among the following peptides is removed during maturation of pro-insulin to insulin?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → C-peptide
Insulin is first made as a pro-hormone (pro-insulin). Like a pro-enzyme, it has to be processed before it becomes a mature, working hormone. Pro-insulin has an extra stretch, the C peptide. During maturation the C peptide is cut out, and the two chains left behind, A and B, stay joined by disulphide bridges to form insulin.
Option (1) B-peptide — Incorrect. The B-peptide (chain B) is one of the two chains of mature insulin. It stays in the hormone.
Option (2) C-peptide — Correct. The C-peptide is the extra stretch of pro-insulin. It is not present in mature insulin because it is removed during maturation.
Option (3) A-peptide — Incorrect. The A-peptide (chain A) is the other chain of mature insulin. It is kept, linked to chain B.
Option (4) D-peptide — Incorrect. There is no D-peptide in pro-insulin or insulin.
NCERT Extract:
Genetically Engineered Insulin – “… In mammals, including humans, insulin is synthesised as a pro-hormone (like a pro-enzyme, the pro-hormone also needs to be processed before it becomes a fully mature and functional hormone) which contains an extra stretch called the C peptide. This C peptide is not present in the mature insulin and is removed during maturation into insulin.”
Figure 10.3 Maturation of pro-insulin into insulin (simplified)