Haemoglobin is a

What is the basic unit of protein structure?

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 properties do amino acids exhibit in solution by acting as electrolytes through their $-COOH$ and $-NH_2$ groups?

How many iron atoms are present in one quaternary structure of $Hb$ (hemoglobin)?

Which of the following macromolecules is found in the structure of hormones and enzymes?