Which of the following statements is true about amino acids?

Amino acids are the building blocks of proteins and are characterized by the presence of both an amine group (-NH2) and a carboxylic acid group (-COOH) attached to a central carbon atom. This unique structure is what differentiates amino acids from other types of organic molecules. The amine group is basic and can accept protons, while the carboxylic acid group is acidic and can donate protons. This dual functional nature allows amino acids to participate in various biochemical reactions, including the formation of peptide bonds, which link amino acids together to form proteins.

The presence of these functional groups is crucial for the unique properties of each amino acid, contributing to their roles in a variety of biological processes including enzyme activity, cellular signaling, and muscle contraction. This statement accurately encapsulates the fundamental chemical structure of amino acids, making it the correct choice.