Draft: Electron Energy Transfer

Metabolic pathways are connected indirectly so that energy released by catabolic pathways is transferred to anabolic pathways. There are two main forms of transfer, and one of them is electrons. Oxidation-reduction, or redox, reactions transfer electrons between molecules. To be oxidized means to lose electrons, and to be reduced means to gain electrons. For every oxidation, there must be a reduction since there are no free electrons in cells. In order to distinguish which molecules will be reduced while another is oxidized, the reduction potential is determined. The reduction potential is the affinity for electrons, or the likelihood of being reduced. It is determined experimentally by comparing the molecule’s reactivity to hydrogen under standard conditions. If its oxidized form has a higher affinity for electrons than hydrogen, it accepts electrons and becomes reduced. On the other hand, if its oxidized form has a lower affinity than hydrogen, its reduced form donates electrons and becomes oxidized. The reduction potential is measured in volts, and a positive potential indicates spontaneity. There is an equation developed that relates the reduction potential to change in free energy, and the presence of a negative sign on one side indicates that a positive reduction potential means a negative change in free energy. This is parallel with the fact that a positive reduction potential means a spontaneous reaction.