| quaternary carbon atom | An atom of carbon to which four other carbon atom's are attached. (05 Mar 2000) |
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| carbon-carbon double bond isomerases | <enzyme> Enzymes that catalyze the shifting of a carbon-carbon double bond from one position to another within the same molecule. Registry number: EC 5.3.3 (12 Dec 1998) |
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| carbon-carbon ligases | <enzyme> Enzymes that catalyze the joining of two molecules by the formation of a carbon-carbon bond. These are the carboxylating enzymes and are mostly biotinyl-proteins. Registry number: EC 6.4 (12 Dec 1998) |
| carbon-carbon lyases | <enzyme> Enzymes that catalyze the cleavage of a carbon-carbon bond by means other than hydrolysis or oxidation. This subclass contains the decarboxylases, the aldehyde-lyases, and the oxo-acid-lyases. Registry number: EC 4.1 (12 Dec 1998) |
| quaternary | 1. Fourth in order. 2. Containing four elements or groups. Origin: L. Quaternarius, from quattuor = four (18 Nov 1997) |
| quaternary structure | The three-dimensional structure of a complex protein, this especially refers to the way the polypeptide subunits fit together. (09 Oct 1997) |
| quaternary syphilis | Any condition indirectly due to syphilis. Synonym: metasyphilis, parasyphilosis, quaternary syphilis. (05 Mar 2000) |
| activated atom | An atom possessing more than normal energy as a result of input of energy. See: excited state. Synonym: excited atom. (05 Mar 2000) |
| atom | <chemistry, physics, radiobiology> A particle of matter indivisible by chemical means. It is the fundamental building block of the chemical elements. The elements, such as iron, lead and sulphur, differ from each other because they contain different kinds of atoms. There are about six sextillion (6 followed by 21 zeros or 6 x 1021) atoms in an ordinary drop of water. According to present day theory, an atom contains a dense inner core (the nucleus) and a much less dense outer domain consisting of electrons in motion around the nucleus. Atoms are electrically neutral. (16 Dec 1997) |
| Bohr's atom | A concept or model of the atom in which the negatively charged electrons move in circular or elliptical orbits around the positively charged nucleus, energy being emitted or absorbed when electrons change from one orbit to another. (05 Mar 2000) |
| radioactive atom | <chemistry, physics> An atom with an unstable nucleus, which emits particulate or electromagnetic radiation (radioactive emission) to achieve greater stability. See: radionuclide, half-life, Becquerel. (05 Mar 2000) |
| recoil atom | The remainder of an atom from which a nuclear particle has been emitted or ejected at high velocity; the remainder recoils with a velocity inversely proportional to its mass. (05 Mar 2000) |
| central atom | <physics> The atom to which the other atoms are bonded in a small molecule. (09 Oct 1997) |
| spectrometry, mass, fast atom bombardment | A mass spectrometric technique that is used for the analysis of a wide range of biomolecules, such as glycoalkaloids, glycoproteins, polysaccharides, and peptides. Positive and negative fast atom bombardment spectra are recorded on a mass spectrometer fitted with an atom gun with xenon as the customary beam. The mass spectra obtained contain molecular weight recognition as well as sequence information. (12 Dec 1998) |
| stripped atom | An atom minus all its electrons; a nucleus. (05 Mar 2000) |
| nuclear atom | <physics, radiobiology> A concept or model of the atom characterised by the presence of a small, massive nucleus at its centre. (05 Mar 2000) |