Amino acids are named after two of their functional groups: the amino group (NH2), which acts like a base, and the carboxyl group (COOH), which acts like an acid. Amino acids also contain a third functional group, often called the R group. In alanine, the R group is a methyl group (CH3). In serine, the R group is a methyl alcohol (–CH2OH). A molecule of alanine is shown next to a molecule of serine. Each molecular structure has an amino group (NH2) on the left side, and a carboxyl group (COOH on the right side.

How do both the similarity and differences among amino acids allow them to form macromolecules with a wide variety of properties?