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 acids is removed prior to insulin formation
(iii) Mature insulin is made up of 51 amino acids arranged in two polypeptide chain -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.

Options

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

Explanation

To determine which statements regarding the structure of proinsulin and mature insulin are not correct, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement (i)**: "Proinsulin is made up of three polypeptide chains - A, B, and C."
- **Analysis**: This statement is correct. Proinsulin indeed consists of three chains: A, B, and the C-peptide.

2. **Statement (ii)**: "C-polypeptide chain with 33 amino acids is removed prior to insulin formation."
- **Analysis**: This statement is also correct. The C-peptide, which is part of proinsulin, is removed during the conversion to mature insulin.

3. **Statement (iii)**: "Mature insulin is made up of 51 amino acids arranged in two polypeptide chains - A and B."
- **Analysis**: This statement is correct. Mature insulin consists of 51 amino acids in total, with two chains: A and B.

4. **Statement (iv)**: "Polypeptide chain A has 30 amino acids and polypeptide chain B has 21 amino acids."
- **Analysis**: This statement is incorrect. In reality, polypeptide chain A has 21 amino acids, and chain B has 30 amino acids, making this statement false.

5. **Statement (v)**: "Polypeptide chains A and B are interconnected by only one S-S linkage."
- **Analysis**: This statement is also incorrect. The two chains are connected by two disulfide (S-S) linkages, not one.

### Conclusion:
The statements that are not correct are:
- Statement (iv): Polypeptide chain A has 30 amino acids and polypeptide chain B has 21 amino acids.
- Statement (v): Polypeptide chains A and B are interconnected by only one S-S linkage.

Thus, the answer to the question is that statements (iv) and (v) are not correct.