| geometric isomerism | A form of isomerism displayed by unsaturated or ring compounds where free rotation about a bond (usually a carbon-carbon bond) is restricted; e.g., the isomerism of a cis-or trans-compound as in oleic acid and elaidic acid. Compare: cis-, entgegen, trans-, zusammen. (05 Mar 2000) |
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| conformational change | <cell biology> Alteration in the shape usually the tertiary structure of a protein as a result of alteration in the environment pH, temperature, ionic strength) or the binding of a ligand (to a receptor) or binding of substrate (to an enzyme). (18 Nov 1997) |
| conformational map | A graphical representation in which the dihedral angle of rotation about the alpha-carbon to carbonyl-carbon bond in polypeptides is plotted against the dihedral angle of rotation about the alpha-carbon to nitrogen bond. Synonym: conformational map. (05 Mar 2000) |
| polymorphism, single-stranded conformational | Variation occurring within a species in the conformation of denatured DNA fragments. These single-stranded DNA fragments are allowed to partially renature in a way that prevents the formation of double-stranded DNA. The fragments are run on polyacrylamide gels under various conditions to detect subtle changes in migration due to altered secondary structure. The resulting bands will align themselves if the fragments are the same, but will misalign if any point mutations are present. Sscps have been used in detecting mutations in various genes, such as oncogenes, tumour suppressor genes, and genes responsible for genetic diseases. (12 Dec 1998) |
| Haworth conformational formula | <biochemistry> Of cyclic sugars, for the pyranoses, these depict those shapes (conformations) on which none, one, or two ring-atoms lie outside the plane of the ring. If there are two such atoms para to each other, they can lie 1) on opposite sides of the plane (trans), giving chair forms, or 2) on the same side of the plane (cis), giving boat forms. For beta-d-ribopyranose, the two chair forms (4C1 and 1C4) are depicted. Similarly, there are six boat conformations. If the two (trans) exoplanar atoms are meta to each other, the conformation is a skew form; if the two atoms are ortho to each other, the conformation is a half-chair form. For the furanoses, the envelope conformations have one ring-atom exoplanar. If there are three adjacent, coplanar ring-atoms (the two exoplanar ring-atoms on opposite sides of the plane), the conformations are twist forms. (05 Mar 2000) |
| single stranded conformational polymorphism | Technique for detecting point mutations in genes by amplifying a region of genomic DNA (using asymmetric PCR) and running the resulting product on a high quality gel. Single base substitutions can alter the secondary structure of the fragment in the gel, producing a visible shift in its mobility. (18 Nov 1997) |
| stereochemical isomerism | The phenomenon whereby compounds whose molecules have the same number and kind of atoms and the same atomic arrangement, but differ in their spatial relationships. (12 Dec 1998) |
| structural isomerism | Isomerism involving the same atoms in different arrangements; e.g., butyric acids, leucine and isoleucine, glucose and fructose. (05 Mar 2000) |
| isomerism | A condition in which several chemical compounds have the same molecular formula (have the same number and type of atoms) but, because those atomsare arranged differently in each, they all have different chemical properties. (09 Oct 1997) |
| optical isomerism | Stereoisomerism involving the arrangement of substituents about an asymmetric atom or atoms (usually carbon) so that there is a difference in the behaviour of the various isomers with regard to the extent of their rotation of the plane of polarised light. Compare: stereoisomerism. (05 Mar 2000) |