Redox Reactions

Redox reactions are fundamental to cellular energy metabolism, involving the transfer of electrons between molecules.

Oxidation, the process of losing electrons, and reduction, the process of gaining electrons, are coupled, as seen in bacterial fermentation where pyruvate is reduced to lactate and the coenzyme, nicotinamide adenine dinucleotide, or NAD, is oxidized.

In biological systems, nicotinamide adenine dinucleotide, flavin adenine dinucleotide, and nicotinamide adenine dinucleotide phosphate commonly function as electron carriers.

NAD⁺ and FAD are primarily involved in catabolic reactions such as cellular respiration.

For example, in the TCA cycle, NAD⁺ accepts two electrons and one proton, forming NADH. FAD accepts two electrons and two protons to form FADH₂.

NADP⁺ accepts electrons to form NADPH, which then provides reducing power for anabolic pathways such as fatty acid synthesis and photosynthesis.

These carriers donate electrons and are recycled back to their oxidized forms —NAD⁺, FAD, and NADP⁺—to maintain the redox balance within the cell.