During the processing of proinsulin into the mature unsulin

Options

A. C-peptide is added to proinsulin
B. C -peptide is removed from proinsulin
C. B-peptide is added to proinsulin
D. B-peptide is removed from proinsulin

Answer

To understand the processing of proinsulin into mature insulin, we can break down the steps involved in this conversion:

### Step-by-Step Solution:

1. **Understanding Proinsulin**: Proinsulin is a precursor molecule that is synthesized in the pancreas. It is a pro-hormone that contains the necessary components to form insulin.

2. **Structure of Proinsulin**: Proinsulin consists of three main parts: the A-chain, the B-chain, and a connecting peptide known as the C-peptide. The C-peptide is an extra stretch that is not present in the mature insulin molecule.

3. **Processing of Proinsulin**: In order to convert proinsulin into mature insulin, the C-peptide must be removed. This is a crucial step because mature insulin is composed only of the A-chain and B-chain, linked together by disulfide bonds.

4. **Enzymatic Action**: The removal of the C-peptide is facilitated by specific enzymes in the Golgi apparatus of the pancreatic beta cells. These enzymes cleave the proinsulin, resulting in the formation of mature insulin.

5. **Final Product**: After the C-peptide is cleaved off, the remaining A-chain and B-chain come together to form the functional insulin molecule. The C-peptide, although removed, can be measured in the blood and is often used as a marker of insulin production.

6. **Conclusion**: Therefore, during the processing of proinsulin into mature insulin, the C-peptide is removed, leading to the formation of the active hormone.

### Answer:
The correct answer is: **C-peptide is removed from pro-insulin**.

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