- Activation
: "This article describes the term used in chemistry and biochemistry.": "For activation (installing) of computer software, see
product activation .": "For activation (calling) of a subroutine in computing, seeSubroutine ."Activation in (bio-)chemical sciences generally refers to the process whereby something is prepared or excited for a subsequent
reaction .Chemistry
In
chemistry , activation ofmolecule s is required for achemical reaction to occur. The phrase energy of activation [ [http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch22/activate.html The Activation Energy of Chemical Reactions ] ] refers to the energy thereactant s must acquire before they can successfully react with each other to produce the products, that is, to reach thetransition state . The energy needed for activation can be quite small and the molecules may have enough energy just from thermal fluctuations the molecules naturally have (i.e. lots of reactions don't have to be heated to proceed). The branch of chemistry that deals with this topic is calledchemical kinetics .Biochemistry
Similarly,
neutron activation is a standardanalytical technique used to analyze for elements, usually,metal s. The sample is placed in a highneutron flux and in thenuclear reaction involved, aneutron is captured by a nucleus. If the resulting newisotope is unstable, it will undergoradioactive decay . This decay can be monitored and the element emitting identified by the identity and energy of the emitted particles. Prompt Gamma Activation Analysis (PGAA) is a rapid, nondestructive, instrumental, nuclear technique which is used for trace and major component analysis of various elements.A number of enzymes are synthesised as inactive
proenzyme s. Only when a polypeptide sequence is cleaved from the end of the protein, in a process called activation, is the enzyme brought to its full level of activity.Immunology
In
immunology , activation is the transition ofleucocytes and othercell types involved in theimmune system . On the other hand, deactivation is the transition in the reverse direction. This balance is tightly regulated, since a too small degree of activation causes susceptibility to infections, while, on the other hand, a too large degree of activation causesautoimmune diseases .Activation and deactivation results from a variety of factors, including
cytokines ,soluble receptor s,arachidonic acid metabolites,steroids ,receptor antagonists ,adhesion molecules , bacterial products and viral products.Electrophysiology
Activation refers to the opening of
ion channels , i.e. the conformational change that allows ions to pass.References
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