Final answer:
The two types of functional groups always found in an amino acid are the amino group (-NH₂) and the carboxyl group (-COOH), both of which are attached to the alpha carbon along with the side chain or R group.
Step-by-step explanation:
Besides the amino acid side chains or R groups, the other two types of functional groups always found in an amino acid are an amino group and a carboxyl group.
The amino group, denoted as (-NH₂), is one of the functional groups that define the molecule as an amino acid. Additionally, every amino acid contains a carboxyl group, represented by the (-COOH) formula. These two functional groups, along with the R group, are all attached to the alpha (a-) carbon.
This alpha carbon is central to the amino acid structure, and it's the chemical nature of the R group that determines whether the amino acid is acidic, basic, polar, or nonpolar, which in turn affects the protein's structure and function.