Answer:
Each amino- acid contain carbon, hydrogen, nitrogen, and oxygen. All the amino- acids are mostly the same by structure because all contain a carbon atom in its center, an amine group, and a carboxyl group.
The unique characteristics that each amino acid has is determined by the R group(side chain) which is attached to its alpha carbon. The R group in each amino acid is different from others.
The simplest amino acid is glycine which does not have any R group so it has a hydrogen atom in place of the R group. So side chain(R group) determines the unique characteristics of each amino acid.