Amino Acids

• Amino acids are organic molecules composed of an amine group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a variable side chain (R group) attached to a central carbon atom.
• There are twenty different amino acids that can be classified into two groups: essential and non-essential. Essential amino acids cannot be synthesised by the human body and must be obtained from the diet. Non-essential amino acids can be produced in the body.
• The properties of an amino acid are determined by the nature of the side chain. Some side chains are hydrophilic (water-loving) due to presence of groups such as -OH, -NH2 and -COOH, whereas some are hydrophobic (water-hating) due to presence of mostly hydrocarbon chains or rings.
• The variable side chains also determine the acid or base character of the amino acid. Generally, amino acids behave as zwitterions (molecules with two opposing charges) in solution due to the amine group acting as a base (proton acceptor) and the carboxyl group as an acid (proton donor).
• Amino acids combine to form polypeptides and proteins through a condensation reaction, in which a molecule of water is eliminated. This bond formed between two amino acids is known as a peptide bond.
• When the pH of an amino acid solution is altered, the amino acid can accept or donate protons, acting as a buffer solution.
• Amino acids can be optically active, possessing a chiral carbon atom. All naturally occurring amino acids (except glycine, which has two hydrogen atoms on the central carbon and thus does not show chirality) are in the L-configuration.
• Structure of proteins, formed by amino acids, can be primary (sequence of amino acids), secondary (folding into alpha-helix or beta-pleated sheet due to hydrogen bonding), tertiary (further three-dimensional folding due to bonding between side chains), and quaternary (combination of two or more polypeptide chains).
• When proteins are exposed to different conditions like heat or change in pH, they lose their specific structure in a process referred to as denaturation.
• Some chemical reagents used for detection of proteins (since they react with amino acids) include Biuret reagent and Ninhydrin.
• Amino acids can be analysed by a technique called chromatography, where the amino acids in a mixture separate based on their different rates of movement due to the differences in their interactions with the stationary and mobile phase.
• Amino acids can be produced industrially via a method known as fermentation, where microorganisms produce the amino acids under controlled conditions.