Which protein is responsible for pigmentation in the animal body?

$A$ protein which exhibits $\beta$-pleated structure is

Identify the type of bond formed between the carboxyl group of one amino acid residue and the amino group of another amino acid residue.

Which one of the following amino acids is not found in proteins?

How many polypeptide chains are present in the structure of hemoglobin?

Hemoglobin consists of two alpha and two beta chains. How many heme groups are present in the structure of hemoglobin?