With regard to insulin choose correct options.

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

(b) The insulin produced by rDNA technology has Cpeptide.

(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.

**Answer:** (a), (c) and (d) only

**Explanation**

(a) C‑peptide is not present in mature insulin.
During insulin biosynthesis, the precursor molecule pro‑insulin contains the A‑chain, B‑chain, and a connecting C‑peptide. After synthesis, specific proteases cleave the C‑peptide, leaving only the A‑chain and B‑chain linked by disulfide bonds. The resulting mature insulin therefore lacks the C‑peptide.

(b) The insulin produced by rDNA technology has C‑peptide.
Recombinant human insulin is produced by inserting the gene for the mature insulin (A‑chain and B‑chain) directly into expression hosts (e.g., *E. coli* or yeast). The construct does not include the C‑peptide sequence, so the purified product does not contain C‑peptide. Hence this statement is false.

(c) The pro‑insulin has C‑peptide.
Pro‑insulin is the initial translation product in pancreatic β‑cells. It consists of the A‑chain, B‑chain, and the connecting C‑peptide. The C‑peptide acts as a linker and is essential for proper folding and formation of the correct disulfide bridges. Therefore, this statement is true.

(d) A‑peptide and B‑peptide of insulin are interconnected by disulphide bridges.
Mature insulin is stabilized by three disulfide bonds: two inter‑chain bridges linking the A‑chain to the B‑chain and one intra‑chain bridge within the A‑chain. These disulfide bonds are crucial for insulin’s three‑dimensional structure and biological activity. Thus, this statement is true.

Combining the truth values, the correct set of statements is (a), (c) and (d) only.