| catabolite repression | <biochemistry, molecular biology> Inducible enzyme systems in some microorganisms (such as the lac operon) that are repressed when a more favoured carbon source, such as glucose, is available. Repression in E. Coli is partially relieved if cAMP is bound to the cAMP catabolite activator protein (cAMP receptor protein, CRP) that binds to DNA upstream of the repressed operon concerned. Catabolite repression (of the respiratory system) is seen in yeast in high glucose concentrations, though the mechanism is different. (16 Mar 1998) |
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| repression | The inhibition of a gene's expression, this is typically caused by the change in the activity of a regulatory protein. (09 Oct 1997) |
| repression-sensitization | Defense mechanisms involving approach and avoidance responses to threatening stimuli. The sensitizing process involves intellectualization in approaching or controlling the stimulus whereas repression involves unconscious denial in avoiding the stimulus. (12 Dec 1998) |
| primal repression | Repression of material never in conscious thought. (05 Mar 2000) |
| end product repression | Catabolite repression in which the catabolite is an end product of a particular pathway. (05 Mar 2000) |
| enzyme repression | The interference in synthesis of an enzyme due to the elevated level of an effector substance, usually a metabolite, whose presence would cause depression of the gene responsible for enzyme synthesis. (12 Dec 1998) |
| positive feedback | <physiology> The return of some of the output of a system as input so as to exert some control in the process. (18 Nov 1997) |
| negative feedback | This occurs where the products of a process can act at an earlier stage in the process to inhibit their own formation. The term was first used widely in conjunction with electrical amplifiers where negative feedback was applied to limit distortion of the signal by the amplification mechanism. Tends to stabilise the process. In contrast to positive feedback. (18 Nov 1997) |
| feedback | <physiology> The return of some of the output of a system as input so as to exert some control in the process. (18 Nov 1997) |
| feedback activation | The activation 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. (05 Mar 2000) |
| feedback control | The regulation of the activity of an enzyme by one of its products. (09 Oct 1997) |
| feedback inhibition | <biochemistry, physiology> The process of the end product of a particular metabolic reaction inhibiting an allosteric enzyme involved in that reaction as the reaction starts again, thus breaking the reaction cycle. (09 Oct 1997) |
| feedback regulation | <physiology> Control mechanism that uses the consequences of a process to regulate the rate at which the process occurs: if, for example: the products of a reaction inhibit the reaction from proceeding (or slow down the rate of the reaction), then there is negative feedback, something that is very common in metabolic pathways. Positive feedback is liable to lead to exponential increase and may be explosively dangerous in some cases. Other examples are the action of voltage dependent sodium channels in generating action potentials and the activation of blood clotting factors V and VIII by thrombin. Without damping, feedback can lead to resonance (hunting) and oscillation in the system. (18 Nov 1997) |
| feedback system | A complex of neuronal circuits whereby a part of the efferent path returns to the input to modulate its activity, thus acting as a governor on the system. See: feedback. (05 Mar 2000) |