amino acid defined in 1951 yearamino acid - amino acid;
amino acid - Organic compound containing both basic amino (NH2) and acidic carobxyl (GOOH) groups. Fundamental constituents of living matter because some hundreds or thousands of amino acid molecules are combined to make each protein molecule. There are twenty different amino-acids commonly found in proteins, and there are a few other rare ones. Essential formula of naturally occurring ones (a-amino-acids) is R-CH(NH2)-COOH, where R is a variable grouping of atoms (fundamentally a carbon chain or ring), an amino group always being attached to the carbon atom next to the carboxyl group. Amino acids are synthesized by autotrophic organisms such as most green plants. Certain ('essential') amino acids must, like vitamins, be obtained from the environment by hetero-trophic organisms. There are eight such for man (valine, leucine, phenylalanine, tryptophan, lysine, isoieucine, methionine, threo-nine), and almost the same list is known for a ciliate, an insect, a bird, and the rat. Other ('non-essentiaP) amino acids are not required from the environment, since the organism can synthesize them, though in some cases only from essential ones. amitosis. Uncommon process of division of nucleus by simple constriction into two halves, without formation of a spindle, dissolution of nuclear membrane, or appearance of chromosomes, all of which occur in mitosis. Formation of daughter nuclei with identical sets of chromosomes, as after mitosis, almost certainly does not result. Whether duplication of chromosomes occurs and the diploid number of chromosomes is approximately maintained in nuclei originating by amitosis is uncertain. Occurs, e.g. in endosperm tissue of flowering plants, macronucleus of Ciliophora (which is highly polyploid).
near amino acid in Knolik
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