Question

Human insulin is synthesised as a prohormone, which contains an extra stretch called

• A. \( \text{A-peptide} \)
• B. \( \text{B-peptide} \)
• C. \( \text{A6-A11 disulfide bond} \)
• D. \( \text{C-peptide} \)

Hint:

Measuring C-peptide levels in the blood is a useful way to see how much insulin a person's body is naturally producing, even if they are taking injected insulin.

Answer 1

The Correct Option is D

Concept: Insulin is a hormone produced by the pancreas that regulates blood sugar levels.
• The production of insulin involves several precursor stages: preproinsulin and proinsulin.
• Mature insulin consists of two polypeptide chains (A and B) linked by disulfide bonds.

Step 1: The Structure of Proinsulin.
Proinsulin is a single long polypeptide chain. It consists of the A-chain and B-chain connected by a third segment of 31 amino acids.

Step 2: Maturation into Active Insulin.
This connecting segment is known as the "C-peptide" (Connecting peptide). Before insulin is released into the blood, enzymes (proteases) cut the C-peptide away. The remaining A and B chains are then held together by disulfide bridges to form the functional hormone. Final Answer: The extra stretch found in the prohormone version of insulin is the C-peptide.