| olfactory tract | A nervelike, white band composed primarily of nerve fibres originating from the mitral cells and tufted cells of the olfactory bulb but also containing the scattered cells of the anterior olfactory nucleus. The tract is closely applied to the ventral surface of the frontal lobe, and attaches itself to the base of the cerebral hemisphere at the olfactory trigone, beyond which it extends in the form of the olfactory striae which distribute their fibres to the olfactory tubercle and, in largest number, to the olfactory cortex on and around the uncus of the parahippocampal gyrus. See: olfactory nerves. Synonym: tractus olfactorius, olfactory peduncle. (05 Mar 2000) |
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| olfactory trigone | A grayish triangular area corresponding to the attachment of the olfactory peduncle ("olfactory nerve" or olfactory tract) to the base of the brain, at the anterior border of the anterior perforated substance. Synonym: trigonum olfactorium. (05 Mar 2000) |
| olfactory tubercle | A small, oval area at the base of the cerebral hemisphere, between the diverging medial and lateral olfactory striae, in the anteromedial part of the anterior perforated substance; it is formed by a small area of allocortex characterised by the presence of the islands of Calleja. Corresponding to a much more prominent structure in nonprimate mammals (especially rodents and insectivores), the olfactory tubercle receives fibres from the olfactory bulb by way of the intermediate olfactory stria; it has efferent connections with the hypothalamus and the mediodorsal nucleus of the thalamus. Synonym: tuberculum olfactorium. (05 Mar 2000) |
| relative molecular mass | The sum of the atomic weight's of all the atoms constituting a molecule; the mass of a molecule relative to the mass of a standard atom, now 12C (taken as 12.000). Relative molecular mass (Mr) is the mass relative to the dalton and has no units. See: atomic weight. Synonym: molecular mass, molecular weight ratio, relative molecular mass. (05 Mar 2000) |
| gram-molecular weight | Molecular weight expressed in grams. Compare: mole. (05 Mar 2000) |
| cloning, molecular | The insertion of recombinant DNA molecules from prokaryotic and/or eukaryotic sources into a replicating vehicle, such as a plasmid or virus vector, and the introduction of the resultant hybrid molecules into recipient cells without altering the viability of those cells. (12 Dec 1998) |
| models, molecular | Models used experimentally or theoretically to study molecular shape, electronic properties, or interactions; includes analogous molecules, computer-generated graphics, and mechanical structures. (12 Dec 1998) |
| molecular | <chemistry> Of, pertaining to or composed of molecules: a very small mass of matter. (18 Nov 1997) |
| molecular behaviour | <psychology> Behaviour described in small response units rather than larger ones; a specific response. Compare: molar behaviour. (05 Mar 2000) |
| molecular biology | <study> The study of the biochemistry of cells, it is closely linked to cell biology, in particular the biochemistry of DNA and cogeners. (16 Dec 1997) |
| molecular biophysics | Biophysics concerned with membrane processes, conformational and configurational properties of macromolecules, bioelectrical phenomena, etc. (05 Mar 2000) |
| molecular chaperones | A family of cellular proteins that mediate the correct assembly or disassembly of other polypeptides, and in some cases their assembly into oligomeric structures, but which are not components of those final structures. It is believed that chaperone proteins assist polypeptides to self-assemble by inhibiting alternative assembly pathways that produce nonfunctional structures. Some classes of molecular chaperones are the nucleoplasmins, the chaperonins, the heat-shock proteins 70, and the heat-shock proteins 90. (12 Dec 1998) |
| molecular clock | This term has two separate uses. 1. <molecular biology> The rate of fixation of mutations in DNA and thus times the rate of genetic diversification. 2. <cell biology> A biological system capable of maintaining up a timing rhythm or pulse. All such clocks are thought to be entrained by a natural oscillator such as the diurnal rhythm. (18 Nov 1997) |
| molecular cloning | <molecular biology> The biological amplification of a specific DNA sequence through mitotic division of a host cell into which it has been transformed or transfected. (09 Oct 1997) |
| molecular conformation | The characteristic three-dimensional shape of a molecule. (12 Dec 1998) |