Question

Which of the following statements regarding the structure of proinsulin and mature insulin are not correct?
(i) Proinsulin is made up of three polypeptide chains- $A$, $B$ and $C$.
(ii) $C$ - polypeptide chain with $33$ amino adds is removed prior to insulin formation.
(iii) Mature insulin is made up of $51$ amino acids arranged in two polypeptide chains- $A$ and $B$.
(iv) Polypeptide chain $A$ has $30$ amino acids and polypeptide chain $B$ has $21$ amino acids.
(v) Polypeptide chains $A$ and $B$ are interconnected by only one $S-S$ linkage.

• A. (i) and (ii)
• B. (iii) and (iv)
• C. (iv) and (v)
• D. (iii), (iv) and (v)

Answer 1

Answer: (C)

Human insulin is made up of $51$ amino acids arranged in two polypeptide chains: $A$, having $21$ amino acids and $B$, with $30$ amino acids. The two polypeptide chains are interconnected by two disulphide bridges.