Nicotinamide adenine dinucleotide

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Nicotinamide adenine dinucleotide (NAD⁺) and nicotinamide adenine dinucleotide phosphate (NADP⁺) are two important cofactors found in cells.

NADH is the reduced form of NAD⁺, and NAD⁺ is the oxidized form of NADH. It forms NADP with the addition of a phosphate group to the 2' position of the adenyl nucleotide through an ester linkage.

Image:NADH-3D-vdW.png

NAD is used extensively in glycolysis and the citric acid cycle of cellular respiration. The reducing potential stored in NADH can be converted to ATP through the electron transport chain or used for anabolic metabolism. ATP "energy" is necessary for an organism to live.

Cells produce NAD from niacin, and use it to transport electrons in redox reactions. During this process NAD picks up electrons and is therefore reduced to NADH, releasing one proton (H⁺).

MH₂ + NAD^{+^{→ NADH + H⁺ + M: + energy, where M is a metabolite.}}

Two hydrogen ions (a hydride ion and an H⁺ ion) are transferred from the metabolite. One electron is transferred to the positively-charged nitrogen, and one hydrogen attaches to the carbon atom opposite to the nitrogen.

Image:NADPplus.png

NADP is used in anabolic reactions, such as fatty acid and nucleic acid synthesis, which require NADPH as a reducing agent. In chloroplasts, NADP is an oxidizing agent important in the preliminary reactions of photosynthesis. The NADPH produced by photosynthesis is then used as reducing power for the biosynthetic reactions in the Calvin cycle of photosynthesis.