Question

Globular protein of ~6kDa consisting of 51 amino acids arranged in two polypeptide chains held by disulphide bridge is

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

Answer 1

The correct option is D Insulin

Recombinant insulin
Insulin is a peptide hormone released as proinsulin which contains additional C-peptide.
Mature insulin has only two peptides A and B joined together by disulfide bonds. It consists of 51 amino acids which contribute to the size of 6kDa

Fibrinogen
Fibrinogen is a homodimeric glycoprotein of size 340kDa. It consists of approximately 452 amino acids.

Glucagon
Glucagon is a peptide hormone consisting of 29 amino acids and has size of approximately 3.4kDa.

Keratin
Keratin is a protein abundantly present in hair. There are various types of keratin present in epithelial cells and hair. Thus, the size of keratin protein ranges from 40kDa to 70kDa in mammals.

Final answer:
(a) Insulin