Nicotinamide adenine dinucleotide is a chemical compound used in many cell reactions. Primarily, it transfers electrons between molecules. This compound is made up of two nucleotides bound together by two phosphate groups. Nicotinamide adenine dinucleotide is used in the metabolism of glucose and the citric acid cycle.
This dinucleotide is found in all cells. A nucleotide consists of a nitrogenous base, meaning it contains nitrogen; a sugar group; and a phosphate group. The nitrogenous bases of nucleotides can vary, but in the case of nicotinamide adenine dinucleotide, the two nitrogenous bases are adenine and nicotinamide.
The nitrogenous base binds to a ribose sugar, which consists of five carbons. The fifth carbon of the ribose sugar is bound to one of the four oxygen atoms of a phosphate group. This makes one nucleotide. A dinucleotide is made when the two phosphate groups bind together.
Nicotinamide adenine dinucleotide is abbreviated as NAD+; the plus sign indicates that the molecule can accept an electron from another molecule. When this occurs, NAD+ is reduced and becomes NADH. The molecule has gained an electron and a hydrogen atom. NADH can, in turn, donate an electron to another molecule. This is called oxidation, and NADH becomes NAD+ — the molecule has lost an electron and a hydrogen atom.
Many of the metabolic pathways in cells utilize NAD+ to transfer electrons. In glycolysis, which is the metabolism of glucose, NAD+ is used to convert glyceraldehyde 3-phosphate into 1,3 bisphosphoglycerate. The process produces two NADH molecules and two hydrogen atoms. This is the fifth step in the metabolic pathway.
NAD+ is also used in the citric acid cycle, which is used to metabolize acetyl-CoA. It is used to convert alpha-ketoglutarate to succinyl-CoA. The process produces NADH and CO2. This is the fourth step in the citric acid cycle. In the reaction, as with the one in glycolysis, an electron is transferred to NAD+ and a hydrogen atom binds to the molecule to create NADH.
Arthur Harden and William Youndin were the British scientists who discovered nicotinamide adenine dinucleotide. They conducted an experiment in which a sample of boiled, filtered yeast extract was added to a sample of unboiled yeast extract. During the experiment, they observed that the fermentation of the unboiled yeast extract increased. They assumed a coferment was responsible for it. Later, the coferment would be identified by Hans von Euler-Chelpin, who described it as a nucleotide sugar phosphate compound.