What is an amino acid?

An amino acid is defined as a molecule that features a central carbon atom bonded to a hydrogen atom, an amino group, a carboxyl group, and a distinctive variable side chain known as the R group. This molecular structure is fundamental to the formation of proteins, as amino acids link together through peptide bonds to create polypeptides. The properties and functions of proteins are deeply influenced by the characteristics of their constituent amino acids, particularly the nature of the variable side chains.

The other choices describe different biochemical components: lipids are not made of amino acids and serve different roles such as energy storage; carbohydrates are primarily composed of sugars and do not include the amino functional groups; and enzymes, while they are often proteins and may include amino acids in their structure, are different in that their primary role is to catalyze biochemical reactions. Thus, the structure and function of an amino acid as described in the correct choice is fundamental to understanding protein synthesis and the biochemical roles of these important organic molecules.