What defines an organic molecule with both an amino group and a carboxyl group?

An organic molecule that contains both an amino group (-NH2) and a carboxyl group (-COOH) is specifically classified as an amino acid. Amino acids are the building blocks of proteins and play a crucial role in various biological processes. The amino group is responsible for the basic properties of the molecule, while the carboxyl group contributes to its acidic nature. This unique combination allows amino acids to participate in peptide bond formation, leading to the synthesis of proteins. Therefore, the defining feature of amino acids—having both an amino and carboxyl group—makes them central to the structure and function of proteins, distinguishing them from other types of organic molecules.

Peptides and polypeptides are chains of amino acids linked by peptide bonds, but they do not inherently define the molecule with both functional groups; rather, they are formed from amino acids. Fatty acids, on the other hand, consist of long hydrocarbon chains with a carboxyl group but lack the amino group entirely. Thus, the presence of both groups unequivocally identifies the molecule as an amino acid.