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s Related Biological Terms:

aspartate proteinase

A type of peptidase that has at its active site two aspartate residues. (see also cysteine proteinase (thiol proteinase); metalloproteinase; serine proteinase)

association analysis

(see linkage disequilibrium)

association constant (Ka)

Reciprocal of Kd (see also pKa)

asymmetrical PCR

A protocol for generation of single-stranded DNA. Unequal amounts of primers are used, so that the first PCR cycles generate equal amounts of each strand of the template but later cycles, which have no more of one of the primers, create only one new strand. McCabe, P.C. (1990) in PCR Protocols: A Guide to Methods and Applications (Innis, M.A., Gelfand, D.H., Sninsky, J.J. and White, T.J., eds.), pp. 76-83, Academic Press, San Diego

asymmetrical reaction

The unequal handling of like groups in a prochiral compound. (see also meso-carbon; Ogston hypothesis)

atomic absorption analysis

A technique for the quantification of small amounts of a metal in solution. Monochromatic light, often generated by excitation of the element in question, passes through a flame in which a test solution is vaporized, and the non-absorbed light, corrected for the excited emission of the metal in the flame, is detected by a photomultiplier. (see also flame photometry)

atomic absorption spectrometry (AA)

A method for quantifying elements, usually metals, in biological samples. The method depends upon the absorption of energy by atoms as they are excited in their electronic ground state. The choice of wavelength depends therefore, on the element to be evaluated and the most convenient energy level at which it can be excited. The sample is vapourized in a flame or electric furnace, and monochromatic light of the desired wavelength is shone through the flame or cloud; absorption of the light is proportional to the number of atoms in the observed volume. In a related technique, flame emission photometry, the small numbers of excited atoms in the flame or cloud are detected as they fall to the ground state and emit light at a wavelength which is characteristic of the element and at an intensity which is proportional to the number of atoms in the observed volume. This proportionality is lost when the concentration of atoms is sufficiently high to allow self-absorption, a phenomenon akin to the inner filter effect of fluorescence spectroscopy, in which emission from the centre of the flame or cloud is absorbed by atoms on its periphery. A standard curve, constructed with known concentrations of the element, allows quantification of experimental samples.

atomic force microscopy (AFM)

Also known as scanning force microscopy; a method for mapping the surface of microscopic (e.g. cellular) and even submicroscopic (e.g. macromolecular) surfaces. As a sharp tip passes over the surface of an object, contact pressure is kept at a minimal constant value by an electronic feedback loop; the whole deflection of the cantilevered tip is measured, for example by deflection of a reflected laser beam. Bustamante, C., Erie, D.A. and Keller, D. (1994) Curr. Opin. Struct. Biol. 4, 750-760

autocatalysis

The activation of a proenzyme preparation by that fraction of it that has already been activated.

autogenous regulation

A phenomenon in which a gene for a single protein is regulated by its own promoter and operator, and constitutes a one-protein operon.

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