Question

Insulin in the human body is secreted by pancreas as
prohormone/proinsulin. The schematic polypetide structure of proinsulin
is given below. This proinsulin needs to undergo processing before it
becomes functional in the body. Answer the questions that follow :
Proinsulin
-
(a)
State the change the proinsulin undegoes 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 polypeptides of a functional insulin chemically
held together?

Answer 1

In mammals, insulin is synthesized in the pancreas within the beta cells. One million to three million pancreatic islets form the endocrine part of the pancreas, which is primarily an exocrine gland.Biosynthesis of Insulin

Insulin is synthesized in significant quantities only in beta cells in the pancreas. The insulin mRNA is translated as a single chain precursor called preproinsulin, and removal of its signal peptide during insertion into the endoplasmic reticulum generates proinsulin.Proinsulin is the prohormone precursor to insulin made in the beta cells of the islets of Langerhans, specialized regions of the pancreas. ... Proinsulin is the final single chain protein structure secreted by cells before cleavage into mature insulin.In response, the pancreas produces insulin, which allows cells to absorb glucose from the blood. ... Measuring the amount of C-peptide in blood indicates how much insulin is being produced. Generally, high C-peptide production indicates high insulin production, and vice versaproblems. Having high levels, also known as hyperinsulinemia, has been linked to obesity, heart disease and cancer (1, 2 , 3 ). High blood insulin levels also cause your cells to become resistant to the hormone's effects.

Answer 2

The answers are as following:

Explanation:

• Chemical change that proinsulin undergoes is cleavage of the C peptide with the aid of two endoproteases i.e. type I and type II endoproteases. This change takes place in islet cells of Langerhans, while proinsulin is transported through the Golgi apparatus .
• Recombinant DNA is a technology scientists developed that made it possible to insert a human gene into the genetic material of a common bacterium. This “recombinant” micro-organism could now produce the protein encoded by the human gene.
• Insulin is composed of two peptide chains referred to as the A chain and B chain. A and B chains are linked together by two disulfide bonds, and an additional disulfide is formed within the A chain.

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