Question

How is the insulin produced by the human body different from the insulin produced by the above-mentioned company?

Answer 1

Insulin, synthesized by the β cells of the islets of Langerhans in the pancreas, controls the level of glucose in the blood. An insulin deficiency manifests itself as diabetes mellitus whose symptoms can be alleviated by a continuing program of insulin injections, thereby supplementing the limited amount of hormone synthesized by the patient’s pancreas. Insulin used for diabetes was earlier extracted from the pancreas of slaughtered cattle and pigs, which caused allergy in some patients and thus called for the use of recombinant DNA technology for the development of synthetic insulin.

Complete answer:
- Insulin is a small protein, having two polypeptides, one has 21 amino acids (A chain), and the other has 30 amino acids (B chain), linked together by disulfide bonds/bridges.
- In humans, insulin is synthesized as a prohormone containing an extra segment of amino acids called the C peptide. This C peptide is not present in the mature insulin and undergoes degradation during the process of maturation into insulin.
- The company Eli Lilly, however, prepared two DNA sequences corresponding to A and B, chains of human insulin, and introduced them in plasmids pBR322 and then transformed E. coli to produce insulin chains.
- Sequences for A and B chains were linked with the lac z gene and introduced into pBR322. The transformed E. coli could be selected by blue-white screening.
- Thus, A and B chains were produced separately, and then later joined by creating disulfide bonds to produce human insulin.

Note: Insulin cannot be orally administered to a diabetic patient because it degrades in the alimentary canal. In a similar way, hormones (growth hormone), vaccines, and antibiotics are made by exploiting biotechnological techniques.