| rare | 1. Not frequent; seldom met with or occurring; unusual; as, a rare event. 2. Of an uncommon nature; unusually excellent; valuable to a degree seldom found. "Rare work, all filled with terror and delight." (Cowley) "Above the rest I judge one beauty rare." (Dryden) 3. Thinly scattered; dispersed. "Those rare and solitary, three in flocks." (Milton) 4. Characterised by wide separation of parts; of loose texture; not thick or dense; thin; as, a rare atmosphere at high elevations. "Water is nineteen times lighter, and by consequence nineteen times rarer, than gold." (Sir I. Newton) Synonym: Scarce, infrequent, unusual, uncommon, singular, extraordinary, incomparable. Rare, Scarce. We call a thing rare when but few examples, specimens, or instances of it are ever to be met with; as, a rare plant. We speak of a thing as scarce, which, though usually abundant, is for the time being to be had only in diminished quantities; as, a bad harvest makes corn scarce. "A perfect union of wit and judgment is one of the rarest things in the world." (Burke) "When any particular piece of money grew very scarce, it was often recoined by a succeeding emperor." (Addison) Origin: F, fr. L. Rarus thin, rare. Source: Websters Dictionary (01 Mar 1998) |
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| rare earth elements | Those elements with atomic numbers 57-71 which closely resemble one another chemically and were once difficult to separate from one another. Synonym: rare earth elements. Origin: Lanthanum, first element of the series (05 Mar 2000) |
| rare earth metal | Those elements with atomic numbers 57-71 which closely resemble one another chemically and were once difficult to separate from one another. Synonym: rare earth elements. Origin: Lanthanum, first element of the series (05 Mar 2000) |
| rare earths | See: lanthanides. (05 Mar 2000) |
| rare-earth screen | An intensifying screen made of a rare-earth oxide phosphor, more efficient than calcium tungstate, especially at the higher kilovoltages used in modern radiography. (05 Mar 2000) |
| rare species | A species of animal or plant that is considered rare, threatened, or endangered. (17 Dec 1997) |
| metals, rare earth | Elements of group IIIb of the periodic table from lanthanum, atomic number 57, to and including lutetium, atomic number 71. (12 Dec 1998) |
| acidic amino acid | An Amino acid with a second acid moiety, e.g., glutamic acid, aspartic acid, cysteic acid. (05 Mar 2000) |
| activated amino acid | The product formed by the condensation of the acyl radical of an amino acid and adenosine 5'-monophosphate (originally in the form of adenosine 5'-triphosphate, with elimination of a pyrophosphoric group). Formed in the first step of protein biosynthesis. Synonym: activated amino acid. (05 Mar 2000) |
| alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid | <chemical> Alpha-amino-2,3-dihydro-5-methyl-3-oxo-4-isoxazolepropanoic acid. An ibotenic acid homolog and glutamate agonist. The compound is the defining agonist for the ampa subtype of glutamate receptors (receptors, ampa). It has been used as a radionuclide imaging agent but is more commonly used as an experimental tool in cell biological studies. Pharmacological action: excitatory amino acid agonists. Chemical name: 4-Isoxazolepropanoic acid, alpha-amino-2,3-dihydro-5-methyl-3-oxo- (12 Dec 1998) |
| alpha-amino acid | Typically, an amino acid of the general formula R-CHNH2-COOH (i.e., the NH2 in the a position); the l forms of these are the hydrolysis products of proteins. In rarer usages, this class of molecules also includes alpha-amino phosphoric acids and alpha-aminosulfonic acids. (05 Mar 2000) |
| alpha-amino acid esterase | <enzyme> Converts alpha-amino acid esters and water to alpha-amino acids and alcohol Registry number: EC 3.1.1.43 Synonym: alpha-amino acid ester hydrolase (26 Jun 1999) |
| alpha-amino-beta-ketoadipic acid | 2-Amino-3-oxo-1,6-hexanedioic acid;an intermediate of porphobilinogen synthesis formed by d-aminolevulinic acid synthase from succinyl-CoA and glycine; it rapidly decarboxylates to d-aminolevulinic acid. (05 Mar 2000) |
| amino acid | <biochemistry> A class of organic molecules that containing an amino group and can combine in linear arrays to form proteins in living organisms. There are twenty common amino acids: alanine, arginine, aspargine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, and valine. They are key components in all living things from which proteins are synthesised by formation of peptide bonds during ribosomal translation of messenger RNA. All the amino acids have the L configuration, except glycine which is not optically active. Other amino acids occurring in proteins, such as hydroxyproline in collagen, are formed by post translational enzymatic modification of amino acid residues in polypeptide chains. There are also several important amino acids, such as the neurotransmitter y aminobutyric acid, that have no relation to proteins. Amino acids can now be produced by biotechnology in bulk using fermentation and biotransformation. Acronym: AA (13 Nov 1997) |
| amino acid activating enzyme | <enzyme> Enzymes catalyzing the formation of a specific aminoacyl-tRNA from an amino acid and adenosine 5'-triphosphate with the concomitant formation of adenosine 5'-monophosphate and pyrophosphate. Synonym: amino acid activating enzyme, aminoacyl-tRNA ligases. (05 Mar 2000) |