Question

Which of the following statement regarding the structure of proinsulin and mature insulin are not correct?

1. Proinsulin is made up of three polypeptide chains - A, B and C.
2. The C-polypeptide chain with 33 amino acids is removed prior to insulin formation.
3. Mature insulin is made up of 51 amino acids arranged in two polypeptide chains - A and B.
4. Polypeptide chain A has 30 amino acids and chain B has 21 amino acids.
5. Polypeptide chains A and B are interconnected by one S-S linkage.

Choose the correct option. 

Options

• I and II

• III and IV

• IV and V

• II, IV and V

Answer 1

IV and V

Explanation:

Statements IV and V are inaccurate and should be amended because human insulin is composed of 51 amino acids organised in two polypeptide chains, chain 'A' having 21 amino acids and chain 'B' having 30 amino acids. Disulphide bridges link the two chains together.