In human insulin is synthesised as a prohormone, which contains an extra stretch called :-

Options

A. A-peptide
B. C-peptide
C. B-peptide
D. `alpha` -peptide

Answer

**Step-by-Step Solution:**

1. **Understanding Proinsulin**: Human insulin is synthesized as a prohormone known as proinsulin. This means that it is initially produced in an inactive form and requires modification to become active.

2. **Structure of Proinsulin**: Proinsulin consists of three chains: Chain A, Chain B, and an additional stretch called Chain C. Chains A and B are linked together by disulfide bridges.

3. **Maturation Process**: During the maturation of proinsulin into active insulin, the C peptide (the extra stretch) is removed. This step is crucial for the conversion of proinsulin into mature insulin.

4. **Resulting Structure**: After the removal of the C peptide, the remaining structure consists of only Chain A and Chain B, which are still connected by disulfide bridges. This is the mature form of insulin.

5. **Biological Activity**: Both the mature insulin and the C peptide are biologically active, but the C peptide is not part of the final active insulin molecule.

6. **Conclusion**: The extra stretch that is removed from proinsulin to form mature insulin is the C peptide.

**Final Answer**: The extra stretch in proinsulin that is removed to form mature insulin is called the **C peptide**.

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