Assertion: The proinsulin contains an extra stretch called as C-peptide
Reason :Insulin consists of two short polypeptide chans A & B that are linked together by disulphide bridges

Options

A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion
B. It both Assertion & Reason are True but Reason is not a correct explanation of the Assetion
C. If Assertion is True but the Reason is False
D. If both Assertion & Reason are false

Answer

To solve the question regarding the assertion and reason related to proinsulin and insulin, we will analyze both statements step by step.

### Step 1: Analyze the Assertion
- **Assertion**: "Proinsulin contains an extra stretch called C-peptide."
- **Explanation**: Proinsulin is a precursor molecule to insulin. It consists of three segments: the A-chain, the B-chain, and the C-peptide. The C-peptide is a connecting peptide that is removed during the conversion of proinsulin to mature insulin. Therefore, this assertion is **true**.

### Step 2: Analyze the Reason
- **Reason**: "Insulin consists of two short polypeptide chains A and B that are linked together by disulfide bridges."
- **Explanation**: Mature insulin is indeed composed of two polypeptide chains (A and B) that are linked by disulfide bonds. This structure is crucial for the biological activity of insulin. Thus, this reason is also **true**.

### Step 3: Determine the Relationship Between Assertion and Reason
- The assertion talks specifically about proinsulin and the presence of C-peptide, while the reason discusses the structure of mature insulin. Although both statements are true, the reason does not explain the assertion because it refers to a different molecule (insulin instead of proinsulin).

### Conclusion
- Since both the assertion and reason are true, but the reason does not correctly explain the assertion, the correct answer is:
- **Both assertion and reason are true, but reason is not a correct explanation of the assertion.**