With regard to insulin choose correct options.

(a) C-peptide is not present in mature insulin.

(b) The insulin produced by rDNA technology has C-peptide.

(c) The pro-insulin has C-peptide.

(d) A-peptide and B-peptide of insulin are interconnected by disulphide bridges.

Choose the correct answer from the options given below.

To determine the correct options regarding insulin, let us analyze each statement step-by-step:

Statement (a): C-peptide is not present in mature insulin.
Insulin is synthesized as a pro-hormone (pro-insulin) which contains an extra stretch of amino acids called the C-peptide (connecting peptide). During maturation, this C-peptide is cleaved off. Therefore, mature insulin consists only of A and B chains and does not contain C-peptide. Hence, statement (a) is correct.

Statement (b): The insulin produced by rDNA technology has C-peptide.
The main challenge in producing recombinant DNA (rDNA) insulin (humulin) was getting it assembled into a mature form without the C-peptide. Recombinant insulin is produced by separately preparing A and B chains in Escherichia coli and then combining them by creating disulfide bonds in vitro. Thus, rDNA-produced insulin does not have C-peptide. Hence, statement (b) is incorrect.

Statement (c): The pro-insulin has C-peptide.
Pro-insulin is the inactive precursor form of insulin. It contains the A-chain, the B-chain, and the connecting C-peptide. Therefore, pro-insulin does have C-peptide. Hence, statement (c) is correct.

Statement (d): A-peptide and B-peptide of insulin are interconnected by disulphide bridges.
Mature insulin is a hormone consisting of two polypeptide chains: polypeptide chain A (with 21 amino acids) and polypeptide chain B (with 30 amino acids). These two chains are linked together by interchain disulfide bonds (disulphide bridges) between specific cysteine residues. Hence, statement (d) is correct.

By evaluating the statements, we find that statements (a), (c), and (d) are correct, while statement (b) is incorrect. Therefore, the correct option is (a), (c) and (d) only.