Question

C-peptide seen in?

• A. In Pre-proinsulin
• B. In Proinsulin
• C. As a combined entity with insulin after secretion
• D. A gastrointestinal proactive molecul

Answer 1

The Correct Option is B

To understand where C-peptide is seen, we should examine the biosynthesis of insulin. Insulin is produced in the beta cells of the pancreas and undergoes several stages:

1. Pre-proinsulin: This is the initial, larger precursor protein that includes a signal peptide, which directs the nascent protein to the endoplasmic reticulum.
2. Proinsulin: In the endoplasmic reticulum, pre-proinsulin is processed by cleaving the signal peptide to form proinsulin. Proinsulin consists of three parts: the insulin A-chain, insulin B-chain, and the C-peptide. Therefore, C-peptide is present in proinsulin as an integral part.
3. Insulin and C-peptide Secretion: Proinsulin is further processed in the Golgi apparatus, where it is cleaved by specific enzymes to form active insulin (composed of the A and B chains linked by disulfide bonds) and the free C-peptide.

The correct option, therefore, is that C-peptide is found in Proinsulin during the insulin biosynthesis process, as it is cleaved from proinsulin before forming active insulin.