| beta-oxidation | <biochemistry> The oxidative breakdown of fatty acids into acetyl-coenzyme A by repeated oxidation at the beta-carbon atom. Oxidation of the beta-carbon (carbon 3) of a fatty acid causes the formation of the beta-keto (beta-oxo) acid analog. This is of importance in fatty acid catabolism, the entire pathway for the catabolism of saturated fatty acids containing an even number of carbon atoms. Beta-oxidation is a part of this pathway and acetyl-CoA is a major product of this pathway. (05 Mar 2000) |
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| beta-oxidation-condensation theory | <biochemistry> That the two carbon fragments split from the fatty acid molecule by beta-oxidation are converted to acetic acid and then condensed to acetoacetic acid. (05 Mar 2000) |
| beta particle | <physics, radiobiology> An electron or positron emitted from a radioactive nucleus during beta decay. (09 Oct 1997) |
| beta pleated sheet | <cell biology> Beta secondary structure in proteins consists of two almost fully extended polypeptide chains lying side by side, linked by interchain hydrogen bonds between peptide C=O and N H groups. The chains may run in the same or opposite directions (yielding parallel or antiparallel structures, respectively). When multiple chains are involved, an extended sheet, the pleated sheet, is formed. (18 Nov 1997) |
| beta-poloidal | <radiobiology> Beta-P is the same as the ordinary beta, except only the poloidal field is used in calculating the magnetic field pressure. Beta-P is greater than 1 in many modern tokamaks. (09 Oct 1997) |
| beta radiation | <radiobiology> Radiant energy from a source of beta rays. (05 Mar 2000) |
| beta ray | 1. <radiobiology> Original term used for electrons (and positrons) ejected from decaying nuclei via beta emission. (Label derives from the old days when we had various kinds of radiation emission, and they were labelled alpha, beta, and gamma (the first letters of the Greek Alphabet) because no one really knew what any of them were.) 2. A stream of positive or negative electrons ejected with high energy from a disintegrating atomic nucleus; most biomedically used isotopes emit negative particles (electrons or negatrons, rather than positrons). Cathode rays are low-energy negative electrons produced in cathode ray tubes, also called television tubes or oscilloscopes. (12 Sep 2000) |
| beta rhythm | <neurology> Brain waves in the electroencephalogram which have a frequency of 18 to 30 per second. They are typical during periods of intense activity of the nervous system, and occur principally in the parietal and frontal regions. (12 Dec 1998) |
| beta sheets | <biochemistry> A structure of proteins where the peptide is extended and stabilised by hydrogen bonding between NH and CO groups of different polypeptide chains or separate regions of the same chain. (05 Mar 2000) |
| beta-sitosterol | Stigmast-5-en-3b-ol; (24R)-24-ethyl-5-cholesten-3b-ol;a phytosterol and anticholesteraemic. Synonym: cinchol. (05 Mar 2000) |
| beta-sulfinylpyruvic acid | <biochemistry> An intermediate product of l-cysteine catabolism in mammalian tissue. Structure: HO2S-CH2-CO-COOH (05 Mar 2000) |
| Beta tests | <psychiatry> A set of pictorially administered mental tests first used in the United States Army in 1917-1918 to determine the relative mental ability of recruits who were illiterate or deficient in reading and writing English, the instructions being given in signs and the test material's pictorial in characters; distinguished from the Army Alpha tests, which were administered at the same time to literate recruits. Synonym: Army Beta tests. (05 Mar 2000) |
| beta thalassaemia | <haematology> Thalassaemia due to one of two or more genes that depress (partially or completely) synthesis of beta-globin chains by the chromosome bearing the abnormal gene. Heterozygous state (A2 t.): thalassaemia minor with Hb A2 increased, Hb F normal or variably increased, Hb A normal or slightly reduced. Homozygous state: thalassaemia major with Hb A reduced to very low but variable levels, Hb F very high level. A disorder characterised by reduced synthesis of the beta chains of haemoglobin. There is retardation of haemoglobin a synthesis in the heterozygous form (thalassaemia minor), which is asymptomatic, while in the homozygous form (thalassaemia major, cooley's anaemia, mediterranean anaemia, erythroblastic anaemia), which can result in severe complications and even death, haemoglobin a synthesis is absent. (05 Mar 2000) |
| beta-thionase | <enzyme> A multifunctional pyridoxal phosphate enzyme. In the second stage of cysteine biosynthesis it catalyses the reaction of homocysteine with serine to form cystathionine with the elimination of water. Chemical name: L-Serine hydro-lyase (adding homocysteine) Registry number: EC 4.2.1.22 (12 Dec 1998) |
| beta-thromboglobulin | <haematology> A platelet-specific protein which is released when platelets aggregate. Elevated plasma levels have been reported after deep venous thrombosis, preeclampsia, myocardial infarction with mural thrombosis, and myeloproliferative disorders. Measurement of beta-thromboglobulin in biological fluids by radioimmunoassay is used for the diagnosis and assessment of progress of thromboembolic disorders. (12 Dec 1998) |