Question

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

• A. (a) and (d) only
• B. (b) and (d) only
• C. (b) and (c) only
• D. (a), (c) and (d) only

Answer 1

The correct option is D (a), (c) and (d) only

Human insulin is a peptide hormone which helps regulate blood sugar level.

In mammals, insulin is synthesised as a prohormone (proinsulin) which needs to be processed before it becomes a fully mature and functional hormone.

This proinsulin contains 3 peptide chains- A, B and C. This C peptide is not present in the mature insulin and is removed during maturation.

Mature human insulin is made up of two polypeptide chains, A and B. The two polypeptide chains are interconnected by disulphide bridges or -S-S- linkages.

In 1983, Eli Lilly, an American company, prepared human insulin by the technique of rDNA technology.

Given below is the procedure followed:

1. Artificial synthesis of DNA sequences, each coding for A and B peptide chains of mature insulin.
2. Plasmid DNA extracted from E.coli is cut with a restriction enzyme. Each of the artificially synthesised insulin-producing genes is inserted into separate bacterial plasmid vectors to form the recombinant DNA using DNA ligase.
3. Transformation of bacteria with recombinant DNA to form the recombinant bacterium.
4. The recombinant bacteria are cultured in a fermentation tank and the bacteria produce A and B chains of insulin separately.
5. Extraction of product from the bacteria is done.
6. This is followed by the creation of disulfide bonds between A and B chains to get the matured form of human insulin.

Therefore, the insulin produced by rDNA technology does not have C Peptide.