Proteins are the most abundant and functionally diverse molecules in living systems, essential for almost every life process. They are linear polymers of amino acids, which can be classified into four main groups based on their side chains: nonpolar, uncharged polar, acidic, and basic. Each amino acid has a carboxyl group, an amino group, and a distinctive side chain bonded to the α-carbon atom. Nonpolar side chains promote hydrophobic interactions, while acidic and basic side chains can donate or accept protons, respectively. The Henderson-Hasselbalch equation describes the quantitative relationship between the pH of a solution and the concentration of a weak acid and its conjugate base. Amino acids can act as buffers within ±1 pH unit of their pKa, with maximal buffering at pH = pKa. The α-carbon of each amino acid (except glycine) is chiral, and only the L-form of amino acids is found in proteins synthesized by the human body.Proteins are the most abundant and functionally diverse molecules in living systems, essential for almost every life process. They are linear polymers of amino acids, which can be classified into four main groups based on their side chains: nonpolar, uncharged polar, acidic, and basic. Each amino acid has a carboxyl group, an amino group, and a distinctive side chain bonded to the α-carbon atom. Nonpolar side chains promote hydrophobic interactions, while acidic and basic side chains can donate or accept protons, respectively. The Henderson-Hasselbalch equation describes the quantitative relationship between the pH of a solution and the concentration of a weak acid and its conjugate base. Amino acids can act as buffers within ±1 pH unit of their pKa, with maximal buffering at pH = pKa. The α-carbon of each amino acid (except glycine) is chiral, and only the L-form of amino acids is found in proteins synthesized by the human body.