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Question
What is the structural difference between proinsulin and mature, biologically active insulin?
Options
Active insulin consists of three separate polypeptide chains linked by peptide bonds
Active insulin contains an extra C peptide segment that is absent in the proinsulin precursor
Proinsulin contains an extra stretch called the C peptide, which is removed during maturation into active insulin
Proinsulin contains only the A chain of 21 amino acids and lacks the B chain
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Solution
Proinsulin is synthesized as a precursor containing the A chain, B chain, and an extra connecting C peptide. During post-translational processing, the C peptide is removed, leaving active insulin consisting of the A chain (21 amino acids) and B chain (30 amino acids) linked by disulphide bonds.
