Reduction roton) ●H Organic molecule NAD coenzyme that includes two (electron carrier Oxidized organic NADH +H+(proton) hydrogen atoms molecule (reduced electron carrier) Oxidati Figure 5.9 Representative biological oxidation. Two electrons and two protons altogether equivalent to two hydrogen atoms) are transferred from an organic substrate molecule to a coenzyme, NAD, NAD* actually receives one hydrogen atom and one electron and one proton is released into the medium. NAD* is reduced to NADH, which is a more energy-rich molecule rganisms use oxidation-reduction reactions in catabolism to extract energy from nutri- ent molecules, such as glucose