| amino acid substitution | The naturally occurring or experimentally induced replacement of one or more amino acids in a protein with another. If a functionally equivalent amino acid is substituted, the protein may retain wild-type activity. Substitution may also diminish or eliminate protein function. Experimentally induced substitution is often used to study enzyme activities and binding site properties. (12 Dec 1998) |
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| base substitution | <molecular biology> One nucleotide base is replaced by another in a DNA molecule. This is also called a point mutation. (09 Oct 1997) |
| conservative substitution | In a gene product, a substitution of one amino acid with another with generally similar properties (size, hydrophobicity, etc), such that the overall functioning is likely not to be seriously affected. (18 Nov 1997) |
| stimulus substitution | <psychology> Learning that takes place when a conditioned stimulus is paired with an unconditioned stimulus. (12 Dec 1998) |
| substitution | 1. The act of putting one thing in the place of another, especially the chemical replacement of one element or radical by some other. 2. A defense mechanism, operating unconsciously, in which an unattainable or unacceptable goal, emotion or object is replaced by one that is attainable or acceptable. Origin: L. Substitutio, from statuere = to place (18 Nov 1997) |
| substitution mutation | A mutation caused by a nucleotide base being replaced by a different one. (09 Oct 1997) |
| substitution product | A product obtained by replacing one atom or group in a molecule with another atom or group. (05 Mar 2000) |
| substitution therapy | Replacement therapy, particularly when replacement is not physiological but entails administration of a substitute. (05 Mar 2000) |
| substitution transfusion | Removal of most of a patient's blood followed by introduction of an equal amount from donors. Synonym: exsanguination transfusion, substitution transfusion, total transfusion. (05 Mar 2000) |
| symptom substitution | An unconscious psychological process by which a repressed impulse is indirectly manifested through a particular symptom, e.g., anxiety, compulsion, depression, hallucination, obsession. Synonym: symptom formation. (05 Mar 2000) |
| freeze substitution | A modification of the freeze-drying method in which the ice within the frozen tissue is replaced by alcohol or other solvent at a very low temperature. (12 Dec 1998) |
| T-cell-rich, B-cell lymphoma | <tumour> A B-cell lymphoma in which more than 90% of the cells are of T-cell origin, masking the large cells that form the neoplastic B-cell component. See: adult T-cell lymphoma. (05 Mar 2000) |
| absorption cell | A small glass chamber with parallel sides, in which absorption spectra of solutions can be obtained. (05 Mar 2000) |
| acid cell | One of the cell's of the gastric glands; it lies upon the basement membrane, covered by the chief cell's, and secretes hydrochloric acid that reaches the lumen of the gland through fine intracellular and intercellular canals (canaliculi). Synonym: acid cell, oxyntic cell. (05 Mar 2000) |
| acidophil cell | A cell whose cytoplasm or its granules stain with acid dyes. (05 Mar 2000) |