Which of the following varies among different animals?

Biological diversity of amino acids is due to the presence of . . . . . . .

Which of the following is the least likely to be involved in stabilising the three-dimensional folding of most proteins?

Which of the following is a heterocyclic amino acid?

Identify the incorrect statement regarding conjugated proteins.

Besides having $C, H, O$,which of the following also contains nitrogen $(N)$?