How many polypeptide chains are found in an insulin precursor molecule?

Options

A. 1
B. 2
C. 3
D. 4

Answer

To determine how many polypeptide chains are found in an insulin precursor molecule, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Insulin Structure**:
- Insulin is a hormone produced by the beta cells of the pancreas, specifically in the islets of Langerhans.

2. **Insulin Precursor**:
- The precursor form of insulin is known as proinsulin. This molecule is inactive and consists of three polypeptide chains: the A chain, the B chain, and the C-peptide.

3. **Polypeptide Chains in Proinsulin**:
- In the proinsulin structure, the A chain and B chain are linked together by disulfide bonds, and the C-peptide connects them. Therefore, proinsulin contains three polypeptide chains in total.

4. **Maturation Process**:
- During the maturation process, the C-peptide is removed, resulting in the active form of insulin, which consists of only the A and B chains. However, the question specifically asks about the precursor molecule.

5. **Conclusion**:
- Since the precursor molecule (proinsulin) has three polypeptide chains, the answer to the question is **3**.

### Final Answer:
The number of polypeptide chains found in an insulin precursor molecule is **3**.