Final answer:
Every amino acid contains an amino group and a carboxyl group attached to the alpha carbon. These functional groups are what distinguish amino acids.
Step-by-step explanation:
Every amino acid contains an amino group (-NH₂) and a carboxyl group (-COOH) attached to the alpha (α) carbon. These two functional groups are what distinguish amino acids and are present in all of them. The side chain or R group, which varies from one amino acid to another, is also attached to the alpha carbon.