Amino acids are the building blocks of proteins, which are the most abundant and functionally diverse molecules in living systems. Proteins perform a wide range of functions, including catalyzing metabolic reactions, providing structural support, and facilitating communication. All proteins are composed of amino acids linked together in a linear chain. There are 20 standard amino acids that are commonly found in mammalian proteins and are coded for by DNA. Each amino acid has a carboxyl group, an amino group, and a unique side chain (R-group) attached to the α-carbon. At physiological pH (around 7.4), the carboxyl group becomes negatively charged, while the amino group becomes positively charged. The side chains determine the properties and functions of amino acids in proteins. Amino acids are classified based on the nature of their side chains: nonpolar, uncharged polar, acidic, or basic. Nonpolar amino acids tend to cluster in the interior of proteins, while polar amino acids are often found on the surface. Some amino acids, such as cysteine, can form disulfide bonds, which are important for protein structure. Others, like serine and threonine, can participate in hydrogen bonding. Acidic amino acids, such as aspartic acid and glutamic acid, have negatively charged side chains, while basic amino acids, such as lysine and arginine, have positively charged side chains. Amino acids can act as buffers, helping to maintain a stable pH in biological systems. The Henderson-Hasselbalch equation describes the relationship between pH, the concentration of a weak acid, and its conjugate base. The isoelectric point (pI) of an amino acid is the pH at which it is electrically neutral. The pI is the average of the pKa values of the two dissociable groups in the amino acid. Only the L-form of amino acids is found in proteins synthesized by the human body. The α-carbon of each amino acid (except glycine) is chiral, meaning it can exist in two mirror-image forms. The L-form is the one found in proteins.Amino acids are the building blocks of proteins, which are the most abundant and functionally diverse molecules in living systems. Proteins perform a wide range of functions, including catalyzing metabolic reactions, providing structural support, and facilitating communication. All proteins are composed of amino acids linked together in a linear chain. There are 20 standard amino acids that are commonly found in mammalian proteins and are coded for by DNA. Each amino acid has a carboxyl group, an amino group, and a unique side chain (R-group) attached to the α-carbon. At physiological pH (around 7.4), the carboxyl group becomes negatively charged, while the amino group becomes positively charged. The side chains determine the properties and functions of amino acids in proteins. Amino acids are classified based on the nature of their side chains: nonpolar, uncharged polar, acidic, or basic. Nonpolar amino acids tend to cluster in the interior of proteins, while polar amino acids are often found on the surface. Some amino acids, such as cysteine, can form disulfide bonds, which are important for protein structure. Others, like serine and threonine, can participate in hydrogen bonding. Acidic amino acids, such as aspartic acid and glutamic acid, have negatively charged side chains, while basic amino acids, such as lysine and arginine, have positively charged side chains. Amino acids can act as buffers, helping to maintain a stable pH in biological systems. The Henderson-Hasselbalch equation describes the relationship between pH, the concentration of a weak acid, and its conjugate base. The isoelectric point (pI) of an amino acid is the pH at which it is electrically neutral. The pI is the average of the pKa values of the two dissociable groups in the amino acid. Only the L-form of amino acids is found in proteins synthesized by the human body. The α-carbon of each amino acid (except glycine) is chiral, meaning it can exist in two mirror-image forms. The L-form is the one found in proteins.