Which molecule acts as a universal hydrogen acceptor?

NAD (Nicotinamide adenine dinucleotide) is recognized as a universal hydrogen acceptor because it plays a crucial role in various metabolic processes by facilitating redox reactions. In these reactions, NAD accepts electrons and a hydrogen ion (proton) to form its reduced form, NADH. This reduction-oxidation process is vital in cellular respiration, particularly in glycolysis and the Krebs cycle, where NAD acts as a key coenzyme that helps transfer energy from metabolic intermediates to the electron transport chain.

The ability of NAD to serve as a hydrogen acceptor is essential for energy production in cells, as it enables the conversion of substrates into usable energy forms, facilitating cellular metabolism. While the other molecules listed have important functions—such as FAD in similar redox reactions, ATP in energy transfer, and CoA in acyl group transfer—the specific role of NAD in accepting hydrogen makes it the universal hydrogen acceptor in biological systems.