Which of the following peptide chain is not present in mature insulin

Options

A. A - peptide
B. B-peptide
C. C-peptide
D. Both (1) and (2)

Answer

To determine which peptide chain is not present in mature insulin, we need to understand the structure of insulin and its precursor, pro-insulin.

### Step-by-Step Solution:

1. **Understanding Peptide Chains**:
- A peptide chain is a molecule formed from two or more amino acids. In the context of insulin, we are specifically looking at the peptide chains that make up the hormone.

2. **Pro-insulin Structure**:
- Insulin is derived from a precursor molecule known as pro-insulin. Pro-insulin consists of three segments: A-peptide, B-peptide, and C-peptide.

3. **Maturation of Pro-insulin**:
- When pro-insulin matures to form insulin, it undergoes a process where the C-peptide is cleaved off. This means that during the maturation process, the C-peptide is removed, leaving only the A-peptide and B-peptide.

4. **Identifying the Peptide Chains in Mature Insulin**:
- After maturation, mature insulin consists solely of the A-peptide and B-peptide. The C-peptide is not part of the final structure of mature insulin.

5. **Conclusion**:
- Therefore, the peptide chain that is not present in mature insulin is the C-peptide.

### Final Answer:
The peptide chain that is not present in mature insulin is **C-peptide**.