- An organic acid which is a building block of proteins. The sequence of amino acids in a protein determines its properties. 20 amino acids are incorporated in human tissue. Of these 12, or 11 in the case of rapidly growing infants, can be synthesized in the body; the remaining 8 or 9 (essential amino acids) must be obtained from food. high-class proteins contain the essential amino acids. They are in alphabetical order: alanine, arginine, aspartic acid, cysteine, cystine, glutamic acid, glycine, histidine, isoleucine, leucine, lysine, methionine, norleucine, ornithine, phenylalanine, serine, threonine, tryptophan, tyrosine and valine.
- noun a chemical compound which is broken down from proteins in the digestive system and then used by the body to form its own protein