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

What is the smallest structural unit (monomer) of a protein called?

$A$: Each protein molecule is a polymer of amino acids.
$R$: There are $20$ types of amino acids in living cells.

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

Protein can be most easily removed by:

Which of the following combine to form proteins?