Question

Which of the following statements about endogenous synthesis of insulin are correct? \[ P. \text{Insulin is synthesized as preproinsulin.} \quad Q. \text{Preproinsulin is converted to proinsulin.} \quad R. \text{Single-site cleavage of proinsulin eliminates C chain.} \quad S. \text{Mature insulin consists of disulfide-linked A and B chains.} \]

• A. P, Q, and R
• B. P, Q, and S
• C. P, R, and S
• D. Q, R, and S

Hint:

Insulin is synthesized as preproinsulin, which is cleaved to form proinsulin and then further cleaved to form mature insulin with disulfide bonds linking the A and B chains.

Answer 1

The Correct Option is B

Step 1: Understanding Insulin Synthesis.
Insulin is synthesized as a precursor molecule called preproinsulin, which is then converted to proinsulin. Proinsulin undergoes a cleavage process to eliminate the C chain, forming mature insulin, which consists of the A and B chains linked by disulfide bonds.
Step 2: Analyzing the Statements.
- (P) Insulin is synthesized as preproinsulin: This is correct. Insulin is initially synthesized as preproinsulin, which includes a signal peptide.
- (Q) Preproinsulin is converted to proinsulin: This is correct. The signal peptide is cleaved, converting preproinsulin to proinsulin.
- (R) Single-site cleavage of proinsulin eliminates C chain: This is incorrect. Proinsulin undergoes a two-step cleavage, not a single-site cleavage, to remove the C chain.
- (S) Mature insulin consists of disulfide-linked A and B chains: This is correct. After the C chain is removed, the A and B chains of proinsulin are linked by disulfide bonds to form mature insulin.
Step 3: Conclusion.
The correct answer is (B) because P, Q, and S are correct statements about insulin synthesis.