Question

__________ is a globular protein of $\sim 6kDa$ consisting of $51$ amino acids, arranged in $2$ polypeptide chains held together by disulphide bridge.

• A. Insulin
• B. Keratin
• C. Glucagon
• D. Fibrinogen

Answer 1

The correct option is A Insulin

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. In most species, the A chain consists of 21 amino acids and the B chain of 30 amino acids.

Although the amino acid sequence of insulin varies among species, certain segments of the molecule are highly conserved, including the positions of the three disulfide bonds, both ends of the A chain and the C-terminal residues of the B chain. These similarities in the amino acid sequence of insulin lead to a three dimensional conformation of insulin that is very similar among species, and insulin from one animal is very likely biologically active in other species. Indeed, pig insulin has been widely used to treat human patients.

So the correct option is 'Insulin'.