Which of the following is not associated with insulin?

• A. Synthesized from proinsulin
• B. Synthesized by B-cells in the pancreas
• C. C-peptide is active form
• D. Two-chain polypeptide

Answer: (C)

Insulin is produced by pancreatic beta cells through a precursor processing pathway where the initial product, proinsulin, is cleaved to form mature insulin and the C-peptide. The mature insulin molecule consists of two chains, A and B, that are linked by disulfide bonds, giving it the active hormone form that regulates glucose. Both insulin and C-peptide are released in equal amounts, but C-peptide itself does not have metabolic activity. Therefore, the statement that C-peptide is the active form is not associated with insulin. The other facts—insulin being synthesized by beta cells, being derived from proinsulin, and being a two-chain polypeptide—are correct.