amino acid small molecule made up of between ten and forty atoms; in addition to carbon, hydrogen, and oxygen, it always contains an amino group. Amino acids are the fundamental building blocks of proteins. Examples include glycine, glutamic acid, alanine, proline, and arginine. Nature makes use of twenty different specific amino acids to construct proteins, which are chains of amino acids bound together with peptide bonds. Short chains are called polypeptides and long ones proteins. In food, amino acids are often found bound together in proteins and also as free amino acids that can have an effect on taste. An example is glutamic acid, which is the basis of umami. Of the twenty natural amino acids, there are nine, known as the essential amino acids, that cannot be produced by the human body and that we must therefore obtain from our food (valine, leucine, lysine, histidine, isoleucine, methionine, phenylalanine, threonine, and tryptophan). Amino acids are chiral molecules, meaning that they are found in two versions that are chemically identical but are mirror images of each other. They are referred to as left-turning (L-amino acids) and right-turning (D-amino acids). Their tastes can vary depending on which way they turn.
