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. H bonds
B. Peptide bonds
C. Ionic bonds
D. Disulphide bridges

Answer

To solve the question regarding the assertion and reason about proinsulin and insulin, we can break it down into clear steps:

### Step-by-Step Solution:

1. **Understanding Proinsulin**:
- Proinsulin is the precursor molecule to insulin. It contains three segments: the A chain, the B chain, and an additional segment known as the C-peptide.

2. **Assertion Analysis**:
- The assertion states that "Proinsulin contains an extra stretch called C-peptide." This is true because proinsulin indeed has a C-peptide that is removed during the conversion to active insulin.

3. **Understanding Insulin Structure**:
- Insulin itself consists of two polypeptide chains, known as the A chain and the B chain. These chains are linked together by disulfide bridges (bonds).

4. **Reason Analysis**:
- The reason states that "Insulin consists of two short polypeptide chains A & B that are linked together by disulfide bridges." This statement is also true.

5. **Relationship Between Assertion and Reason**:
- While both statements are correct, the reason does not explain the assertion. The assertion specifically refers to the presence of the C-peptide in proinsulin, while the reason describes the structure of insulin, which does not include the C-peptide.

6. **Conclusion**:
- Therefore, the correct answer is that the assertion is true, the reason is true, but the reason does not explain the assertion.

### Final Answer:
- Assertion: True
- Reason: True
- Explanation: The reason does not explain the assertion.