activation (ak-ti-va´shun)

1. The act of rendering active. 2. An increase in the energy content of an atom or molecule, through the raising of temperature, absorption of light photons, etc., which renders that atom or molecule more reactive. 3. Techniques of stimulating the brain by light, sound, electricity, or chemical agents, in order to elicit abnormal activity in the electroencephalogram. 4. Stimulation of peripheral nerve fibers to the point that action potentials are intiated. 5. Stimulation of cell division in an ovum by fertilization or by artificial means. See cross-section. 6. The act of making radioactive.
amino acid a. the formation of the amino acyl adenylate derivative (e.g., during protein biosynthesis).
EEG a. the low voltage, fast pattern of attentive wakefulness.
feedback a. a. of an enzyme by an end product of a biochemical pathway in which that enzyme plays a part. For example, the activation of factors VIII and V by thrombin during blood clotting.
feed-forward a. the a. of an enzyme by a precursor of the substrate of that enzyme.
gene a. the process of a. of a gene so that it is expressed at a particular time. This process is crucial in growth and development.


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