Question

The number of amino acids and the molecular weight of human insulin is
A. 51 amino acids, 58 k. Da.
B. 41 amino acids, 51 k. Da.
C. 51 amino acids, 50 k. Da.
D. 70 amino acids, 55 k. Da.

Answer 1

Hint: Insulin has two chains having 21 and 30 amino acids. The average molecular weight of insulin is near about 60 k. Da.

Complete answer:
Insulin is a hormone secreted from beta cells of pancreatic islets.
It is made up of 2 polypeptide chains namely A and B.
Each chain is made up of a specific sequence of amino acid residues that are connected by peptide bonds.
In humans, chain A of insulin has 21 amino acids, and chain B has 30 amino acid residues.
Hence, insulin contains 51 amino acids.
The molecular weight is 58 kilo Dalton or kDa.

Hence, the correct answer is option A. 51 amino acids, 58 k. Da.

Additional information:
Insulin is an anabolic hormone of the body.
It regulates the metabolism of carbohydrates, fats and protein.
It promotes the absorption of glucose from the blood into liver, fat and skeletal muscle cells.
In the liver and muscles the absorbed glucose is converted into either glycogen or fats by glycogenesis and lipogenesis respectively.
Low insulin levels in the blood have the opposite effect in the body that promotes the catabolism of reserve body fat.
Insulin was discovered by Frederick Banting and Charles Herbert Best.
They are the first one to isolate insulin from dog pancreas.
Frederick Sanger first sequenced the amino acid residues of insulin. Insulin is the first protein that was sequenced fully.

Note: The insulin is synthesized from pro-insulin that contains more than 51 amino acids. But that form of insulin is not active. There is a variable C chain in the insulin that makes the pro-insulin inactive. When the C chain is removed from pro-insulin by the body during synthesis, the active form of insulin with 51 amino acids residues synthesized.