Question

Insulin in the human body is secreted by pancreas as prohormone/proinsulin. The schematic polypeptide structure of proinsulin is given below. This proinsulin needs to undergo processing before it becomes functional in the body. Answer the questions that follow:

(a) State the change the proinsulin undergoes at the time of its processing to become functional.

(b) Name the technique the American company Eli Lilly used for the commercial production of human insulin.

(c) How are the two polypeptide of a functional insulin chemically held together? 

Or 

Explain the applications of rDNA technology to produce insulin. Give well define diagram producing humulin via genetic engineering.

Answer 1

(a) Pro - insulin is naturally synthesised by human and other mammals contain a c - peptide chain that does not found in mature insulin. Pro - insulin contain three chains A, B and C, when pro - insulin undergoes maturation c - peptide separate out from insulin and fully mature insulin only contain two A and B chains, bonded with di - sulfide bond.

(b) In 1983, American company Eli Lilly designed two DNA sequence, similar to A and B chain of insulin. E. coli bacteria used to produce A and B chains in culture medium separately. Though disuifide linkage both the chains are exactly like mature insulin. This artifically synthesised insulin is named humulin, which is very safe and cause no ellergy.

(c) Two separately produced A and B chains of insulin are bond with disulfide linkage (—S—S—).