8.8: Electron Carriers
Electron carriers are compounds that shuttle around high-energy electrons—the cell’s currency of extractable energy—via redox reactions—coordinated states of oxidation and reduction, respectively losing and gaining these negatively charged atoms.
For instance, one principal compound is nicotinamide adenine dinucleotide, or NAD, named so because one ribose ring has an adenine base, while the other has nicotinamide attached to the first carbon atom. At the fifth carbon position, these two nucleotides are joined by two phosphate groups.
During metabolism, NAD, as a coenzyme, binds to an enzyme that catalyzes the reactions, and acts as an oxidizing agent, removing two hydrogen atoms—along with a pair of electrons—from a reactant, like a sugar.
The electrons are then transferred to the positively charged nitrogen, and a hydrogen atom is attached to the opposite carbon, forming NADH. In the end, the extra hydrogen protons are left in the cytoplasm, and NADH shuttles its electrons to the mitochondrial membrane, where they enter the electron transport chain, and the carriers can continue to undergo redox reactions.