The basic chemical structure of an amino acid consists of a central carbon atom (C) bonded to four groups: an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom (-H), and a variable side chain or R group that determines the unique characteristics of each amino acid. There are 20 standard amino acids, each with a different R group, which contributes to the diversity of proteins formed by linking these amino acids in specific sequences. The sequence and composition of amino acids ultimately define the structure and function of proteins within biological systems.