Answer:
An amino acid can be described as a macromolecule consisting of an amino group, carboxyl group and an R- group.
The R-group determines the specificity of each amino acid. The size, polarity, pH, temperature, function etc of an amino acid are all dependent on this unique R group.
Structurally, the R group is present as a side chain which determines all the chemical properties for that amino acid. The R group is also termed as a variable group.