| temperature sensitive mutation | <genetics, molecular biology> A type of conditional mutation in organism, somatic cell or virus that makes it possible to study genes whose total inactivation would be lethal. Such ts mutations can also make possible studies of the effect of reversible switching by temperature changes) in expression of the mutated gene. The usual mechanism of temperature sensitivity is that the mutated gene codes for a protein with a temperature dependent conformational instability, so that it possesses normal activity at one temperature (the permissive temperature), but is inactive at a second (nonpermissive) temperature. (18 Nov 1997) |
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| transition mutation | A point mutation involving substitution of one base-pair for another, i.e., replacement of one purine for another and of one pyrimidine for another pyrimidine without change in the purine-pyrimidine orientation. (05 Mar 2000) |
| transversion mutation | A point mutation involving base substitution in which the orientation of purine and pyrimidine is reversed, in contradistinction to transition mutation. (05 Mar 2000) |
| umber mutation | A mutation yielding the termination codon UGA, resulting in premature termination of a polypeptide chain. Compare: suppressor mutation. Synonym: opal mutation. (05 Mar 2000) |
| unstable mutation | <molecular biology> A mutation that has a high likelihood of reverting to its original form. (13 Nov 1997) |
| up mutation | <molecular biology> Refers to any mutation in the promoter region of a gene which can trigger transcription initiation. (09 Oct 1997) |
| up promoter mutation | A mutation that increases the frequency of initiation of transcription. (05 Mar 2000) |
| forward mutation | Any mutation which renders a formerly functional gene nonfunctional. Compare: back mutation. (09 Oct 1997) |
| frameshift mutation | <molecular biology> A type of mutation that results from insertion or deletion of a single nucleotide into, or from, an open reading frame in the normal DNA sequence. Normally, the genetic code is read in the wrong frame, three nucleotides at a time, and the entire sequence downstream of the mutation, is translated into a polypeptide with a garbled amino acid sequence from the mutated codon onwards. These mutations may be induced by certain types of mutagens or may occur spontaneously and usually result in the generation, downstream, of nonsense, chain termination codons. Synonym: addition mutation, addition-deletion mutation, deletion mutation, reading-frameshift mutation. (21 Jun 2000) |
| lethal mutation | <genetics, molecular biology> Mutation that eventually results in the death of an organism carrying the mutation. (18 Nov 1997) |
| A chain | A polypeptide component of insulin containing 21 amino acyl residues, beginning with a glycyl residue (NH2-terminus); insulin is formed by the linkage of an A chain to a B chain by two disulfide bonds; the amino-acid composition of the A chain is a function of species. Synonym: glycyl chain. In general, one of the polypeptides in a multiprotein complex. (05 Mar 2000) |
| alpha chain disease | A vague or indefinite term; could be used for alpha-heavy-chain disease (a lymphoplasma cell proliferative disease usually seen in Mediterranean men, characterised by intestinal involvement with steatorrhoea, often progressive with fatal outcome) or a thalassaemia (a genetic abnormality in the alpha globin chain of haemoglobin). (05 Mar 2000) |
| amino acids, branched-chain | Amino acids which have a branched carbon chain. (12 Dec 1998) |
| B chain | A polypeptide component of insulin containing 30 amino acyl residues, beginning with a phenylalanyl residue (NH2-terminus); insulin is formed by the linkage of a B chain to an A chain by two disulfide bonds; the amino-acid composition of the B chain is a function of species. Synonym: phenylalanyl chain. (05 Mar 2000) |
| behaviour chain | Related behaviours in a series in which each response serves as a stimulus for the next response. (05 Mar 2000) |