The number of $>C=O$ groups present in a tripeptide $Asp-Glu-Lys$ is.......

In the following compound,the favourable site/s for protonation is/are:
(Image description: Adenine structure with labels $a$ on the exocyclic $-NH_2$ group,$b$ on the pyrimidine ring nitrogen,$c$ on the other pyrimidine ring nitrogen,$d$ on the imidazole ring nitrogen,and $e$ on the imidazole ring $-NH-$ group.)

What type of compound the Legumelin is?

Nitrogen is an essential constituent of all

The water-soluble protein is:

Which type of biomolecules have some structural similarity with synthetic polyamides? What is this similarity?