| ribonucleic acid | <molecular biology> A nucleic acid found in all living cells. Plays a role in transferring information from DNA to the protein-forming system of the cell. (16 Dec 1997) |
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| masked messenger RNA | <molecular biology> Long lived and stable mRNA found originally in the oocytes of echinoderms and constituting a store of maternal information for protein synthesis that is unmasked (derepressed) during the early stages of morphogenesis. In these early stages the rate of cell division is so rapid that transcription from the embryonic genome cannot occur. Undoubtedly not restricted to oocytes and the term can be applied to any mRNA which is present in inactive form. (18 Nov 1997) |
| messenger | 1. That which carries a message. 2. Having message-carrying properties. First messenger, a hormone that binds to a receptor on the surface cell and, in so doing, communicates with intracellular metabolic processes. Second messenger, an intermediary molecule that is generated as a consequence of hormone-receptor interaction; e.g., see adenosine 3',5'-cyclic monophosphate; guanosine 3',5'-cyclic monophosphate; calcium; inositide. (05 Mar 2000) |
| messenger-like RNA | An ill-defined form of RNA, of high molecular weight, that never leaves the nucleus and is thought to be the precursor of messenger RNA. (05 Mar 2000) |
| messenger RNA | <molecular biology> Single stranded RNA molecule that specifies the amino acid sequence of one or more polypeptide chains. This information is translated during protein synthesis when ribosomes bind to the mRNA. In prokaryotes, mRNA is normally formed by splicing a large primary transcript from a DNA sequence and protein synthesis starts while the mRNA is still being synthesised. Prokaryote mRNAs are usually very short lived (average t 1/2 is 5mins.). In contrast, in eukaryotes the primary transcripts (HnRNA) are synthesised in the nucleus and they are extensively processed to give the mRNA that is exported to the cytoplasm where protein synthesis takes place. This processing includes the addition of a 5' 5' linked 7 methyl guanylate cap at the 5' end and a sequence of adenylate groups at the 3' end, the poly A tail, as well as the removal of any introns and the splicing together of exons, only 10% of HnRNA leaves the nucleus. Eukaryote mRNAs are comparatively long lived with a half life ranging from 30minutes to 24 hours. (27 Jun 1999) |
| second messenger | <molecular biology> In many hormone sensitive systems the systemic hormone does not enter the target cell but binds to a receptor and indirectly affects the production of another molecule within the cell, this diffuses intracellularly to the target enzymes or intracellular receptor to produce the response. This intracellular mediator is called the second messenger. Examples include cyclic AMP, cyclic GMP, IP3 and diacylglycerol. (18 Nov 1997) |
| second messenger systems | Systems in which an intracellular signal is generated in response to an intercellular primary messenger such as a hormone or neurotransmitter. They are intermediate signals in cellular processes such as metabolism, secretion, contraction, phototransduction, and cell growth. Examples of second messenger systems are the adenyl cyclase-cyclic AMP system, the phosphatidylinositol diphosphate-inositol triphosphate system, and the cyclic GMP system. (12 Dec 1998) |
| Rambourg's chromic acid-phosphotungstic acid stain | <technique> A stain for glycoproteins, used with an electron microscope, with which ultrathin tissue sections reveal complex carbohydrates in the same locations as shown by Rambourg's periodic acid-chromic methenamine-silver stain. (05 Mar 2000) |
| a1-acid glycoprotein | <biology> Plasma protein of mammals and birds, 38% carbohydrate. In humans a single chain glycoprotein of 39 kD. Increased levels are associated with inflammation, pregnancy and various diseases. (18 Nov 1997) |
| abscisic acid | <biochemistry> A lipid hormone that inhibits cell growth in plants, it is associated with fruit drop, leaf death and seed dormancy. It is synthesised in the plastids from carotenoids. This hormone helps plants deal with water loss, and its effects can be reversed with gibberellins. (06 May 1997) |
| abscisic acid 8'-hydroxylase | <enzyme> Catalyses conversion of abscisic acid to 8'-hydroxyabscisic acid, which rearranges to phaseic acid Registry number: EC 1.14.99.- Synonym: aba 8'-hydroxylase (26 Jun 1999) |
| acetic acid | <chemical> The acid most commonly associated with vinegar, it is the most commercially important organic acid and is used to manufacture a wide range of chemical products, such as plastics and Acetobacter but, except for making vinegar, is usually made through synthetic processes. Derivatives of acetic acid which may be formed by substitution reactions. Mono- and di-substituted, as well as, halogenated compounds have been synthesised. Experimentally, alpha- and n2- substituted acetic acids have been examined for their anti-inflammatory activity and effect on the central nervous system respectively. Additionally, limited exposure data has been collected on dibromo and dichloroacetic acids to determine whether they pose health effects. Synonym: ethanoic acid. (26 Jun 1999) |
| acetoacetic acid | CH3COCH2COOH;one of the ketone bodies, formed in excess and appearing in the urine in starvation or diabetes. Synonym: diacetic acid. (05 Mar 2000) |
| acetohydroxamic acid | C2H5NO2; N-Hydroxyacetamide;an inhibitor of urease, used as adjunctive therapy in chronic urea-splitting urinary infections. (05 Mar 2000) |
| acetrizoic acid | <chemical> A water-soluble, iodinated radiographic contrast medium, used as sodium acetrizoate in hysterosalpingography. Pharmacological action: contrast media. Chemical name: Benzoic acid, 3-(acetylamino)-2,4,6-triiodo- (12 Dec 1998) |