Answer:
The correct option is: b. the side chain
Explanation:
Amino acids are biomolecules that contain an alpha-carbon (α-C) attached to two functional groups- carboxyl group (-COOH) and amine group (-NH₂), and an organic side chain (-R).
The carboxyl and amine functional groups are common in all amino acids but the side chain is distinctive to each amino acid.
Thus the amino acids can be easily classified on the basis of the properties of this organic side chain.
Therefore, the various amino acids have different side chains.
