Question

Study the following statements (A-D).
A. In mammals, insulin is synthesised as a prohormone.
B. Mature insulin consists of three short polypeptide chains.
C. Humulin is synthesised using Escherichia coli.
D. Insulin helps in gluconeogenesis.
How many of the above statements are true?

• A. Three
• B. Two
• C. Four
• D. One

Answer 1

The correct option is B Two

The endocrine part of the pancreas (islets of Langerhans) produces hormones. Beta cells of islets of Langerhans produce insulin. Proinsulin is the biologically inactive precursor synthesised by beta cells which then undergoes cleavage into mature insulin. So statement A is correct.

Proinsulin possesses three peptide fragments - A, B and C. It is converted into the bioactive hormone insulin by the removal of the C peptide. Mature insulin possesses only A and B chains, that means only 2 polypeptide chains. So statement B is incorrect.

Humulin is the human insulin produced by recombinant DNA technology using a laboratory strain of Escherichia coli. It possesses the same number of amino acids which is present in human insulin. So statement C is correct.

Insulin stimulates glycogenesis (hepatic conversion of glucose into glycogen for storage) and glycolysis (breakdown of glucose). So statement D is incorrect.

Glucagon produced by the alpha cells of islets of Langerhans elevates the concentration of glucose in the blood by promoting glucogenesis (formation of glucose from any product of glycolysis), gluconeogenesis (generation of glucose from certain non-carbohydrate carbon source) and glycogenolysis (hepatic conversion of glycogen into glucose).