Minimum amount of energy (heat, electromagnetic radiation, or electrical energy) required to activate atoms or molecules to a condition in which it is equally likely that they will undergo chemical reaction or transport as it is that they will return to their original state. Chemists posit a transition state between the initial conditions and the product conditions and theorize that the activation energy is the amount of energy required to boost the initial materials “uphill” to the transition state; the reaction then proceeds “downhill” to form the product materials. Catalysts (including enzymes) lower the activation energy by altering the transition state. Activation energies are determined by experiments that measure them as the constant of proportionality in the equation describing the dependence of reaction rate on temperature, proposed by Svante Arrhenius. Seealso entropy, heat of reaction.
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AID is currently thought to be the master regulator of secondary antibody diversification. It is involved in the initiation of three separate immunoglobulin (Ig) diversification processes, somatic hypermutation (SHM), class switch recombination (CSR) and gene-conversion (GC).
AID has been shown in vitro to be active on single stranded DNA, and has been shown to require active transcription in order to exert its deaminating activity. The involvement of Cis-regulatory factors is suspected as AID activity is several orders of magnitude higher in the immunoglobulin "variable" region than other regions of the genome that are known to be subject to AID activity. This is also true of artificial reporter constructs and transgenes that have been integrated into the genome.
Parthenogenetic activation of porcine oocytes and isolation of embryonic stem cells-like derived from parthenogenetic blastocysts.(Report)
Oct 01, 2007; ABSTRACT : These experiments were carried out to optimize the parameters of electrical activation, methods of...