Arrange the following steps of genetically engineered insulin production.

(A) Isolation and purification of the insulin gene from beta cells of the pancreatic islets

(B) Expression of gene in host cell

(C) Joining the two polypeptides by disulfide bonds

(D) Cloning of insulin gene in Escherichia coli cloning host cell

Choose the correct answer from the options given below:

(A), (D), (B), (C)

The correct answer is Option (2) → (A), (D), (B), (C)

(A) Isolation and purification of the insulin gene from beta cells of the pancreatic islets

(D) Cloning of insulin gene in Escherichia coli cloning host cell

(B) Expression of gene in host cell

(C) Joining the two polypeptides by disulfide bonds

Insulin is composed of two short polypeptide chains, chain A and chain B, connected by disulfide bridges. In mammals, including humans, insulin is initially synthesized as a pro-hormone, which includes an additional segment known as the C peptide. During maturation into insulin, this C peptide is removed, and the insulin becomes fully mature and functional.Insulin used for diabetes was earlier extracted from pancreas of slaughtered cattle and pigs. Insulin from an animal source, though caused some patients to develop allergy or other types of reactions to the foreign protein.

In 1983, the American pharmaceutical company Eli Lilly successfully created two DNA sequences corresponding to the A and B chains of human insulin. These DNA sequences were inserted into plasmids, which were then introduced into Escherichia coli (E. coli) bacteria. Inside the E. coli cells, the A and B chains of insulin were produced independently as separate protein molecules. After extracting the A and B chains from the bacterial culture, they were combined and linked together through the formation of disulfide bonds, resulting in the creation of fully functional human insulin. This achievement marked a significant milestone in medicine, as it enabled the production of human insulin using recombinant DNA technology, revolutionizing the treatment of diabetes worldwide.