Final answer:
Amino acids are the monomers that make up proteins and have a common structure consisting of a central carbon atom bonded to an amino group, a carboxyl group, and a hydrogen atom. The R group is the variable component of amino acids.
Step-by-step explanation:
Amino acids are the monomers that make up proteins and they all have the same fundamental structure consisting of a central carbon atom bonded to an amino group (NH2), a carboxyl group (COOH), and a hydrogen atom. The fourth component of an amino acid is the R group, which varies among the different amino acids. These components are common to all amino acids and are responsible for their structure, function, and diversity.