This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Proteins and Amino Acids, Subject name: Biochemistry
Number of amino acids in A chain and B chain of insulin is: 
Select and explain. 
A. 30, 21, B. 28, 32, C. 32, 28, D. 21, 30
D: 21, 30
Answer: D: 21, 30 
Explanation: Ans: d (21 and 30) Ref: Vasudevan,4th ed, p. 108Insulin is a protein hormone with 2 polypeptide chains; the A chain with 21 amino acids and B chain with 30 amino acids.Insulin:T 1/2 of insulin is 5 minutes.Normal daily insulin secretion is 50 units.Tissues independant of insulin - RBC, brain, renal medullary cells, placenta.Amino acids stimulating insulin secretion - leucine and arginine.Pork insulin differs from human insulin by only one amino acid residue.