When NAD becomes NADH, it is being reduced and gaining chemical energy.
Nicotinamide adenine dinucleotide (NAD), a coenzyme, can exist in two forms, NAD⁺ (oxidized) and NADH (reduced form).
Electrons and protons released in catabolism reactions are attached to NAD⁺. The conversion of NAD⁺ to NADH is important reaction for production of ATP during the cellular respiration.
Reduction is lowering oxidation number because element, ion or compound gain electrons.
Chemical equation for reaction of reduction of NAD⁺ (see picture below):
NAD⁺ + 2e⁻ + H⁺ → NADH
Nicotinamide adenine dinucleotide (NAD) is made of two nucleosides joined by pyrophosphate.
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