- Amino acid
- One of the 20 building blocks of protein. The sequence of amino acids in a protein and, hence, the function of that protein are determined by the genetic code in the DNA. Amino acids are molecules that (in technical terms) contain a basic amino (NH2) group, an acidic carboxyl (COOH) group and a side chain attached to an alpha carbon atom. The 20 amino acids are alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, and valine. The term "amino acids" dates to the middle of the 19th century. The idea that amino acids are "Bausteine" (building stones) came from the Nobel Prize winning German biochemist Albrecht Kossel (1853-1927).
* * *An organic acid in which one of the hydrogen atoms on a carbon atom has been replaced by NH2. Usually refers to an aminocarboxylic acid. However, taurine is also an a.. SEE ALSO: α-a..- activated a. SYN: aminoacyl adenylate.- basic a. an a. containing a second basic group (usually an amino group); e.g., lysine, arginine, ornithine. SYN: dibasic a..- a. dehydrogenases enzymes catalyzing the oxidative deamination of amino acid s to the corresponding oxo (keto) acids; two relatively nonspecific varieties exist, l and d, for which l-amino acids and d-amino acids are the respective substrates; the products include NH3 and a reduced hydrogen acceptor (NADH in the l case); a. dehydrogenases of greater specificity exist ( e.g., glycine dehydrogenase). Cf.:a. oxidases.- essential amino acid s α-amino acid s nutritionally required by an organism and which must be supplied in its diet ( i.e., cannot be synthesized by the organism) either as free a. or in proteins.- nonessential amino acid s those amino acid s that may be synthesized by an organism and are thus not required as such in its diet.- nonpolar a. an α-a. in which the functional group attached to the α-carbon ( I.E., R in RCH(NH2)COOH) has hydrophobic properties; E.G., valine, leucine, α-aminobutyrate.- a. oxidases flavoenzymes oxidizing, with O2 and H2O, either l- or d-amino acids specifically, to the corresponding 2-keto acids, NH3 and H2O2. Cf.:a. dehydrogenases, yellow enzyme.- polar a. an α-a. in which the functional group attached to the α-carbon ( i.e., R in RCH(NH2)COOH) has hydrophilic properties; e.g., serine, cysteine, homocysteine.
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* * *an organic compound containing an amino group (-NH2) and a carboxyl group (-COOH). Amino acids are fundamental constituents of all protein. Breakdown of proteins found in the body yields the following amino acids: alanine, arginine, asparagine, aspartic acid, cysteine, cystine, glutamic acid, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, and valine. Some of these amino acids can be synthesized by the body; others, the essential amino acid, must be obtained from protein in the diet. Certain amino acids present in the body are not found in proteins; these include citrulline, ornithine, taurine, and gamma-aminobutyric acid acid.
* * *see at amino.
Medical dictionary. 2011.