The Nicotinamide Adenine Dinucleotide (NAD) molecule in 3-D

NAD (Nicotinamide Adenine Dinucleotide) is a hydrogen acceptor, used as a coenzyme in many reactions especially in respiration to transfer (pairs of) hydrogen atoms to other molecules. Dehydrogenation - the removal of hydrogen - is effectively a form of oxidation. Accompanying this is the acceptance/gain and donation/loss of electrons.

NAD consists of two nucleotides, joined by their phosphate groups . On either side of the central phosphate groups are 5-membered ribose rings, attached to other rings (bases) containing nitrogen atoms (blue). On one end of the molecule is a double ring structure - the base adenine - and at the other end is a slightly simpler single ring structure - nicotinamide - which is a derivative of vitamin B3.

The oxidised form of the molecule carries a positive charge (so it may be called NAD+) due to the arrangement of bonds on one of the nitrogen atoms in the nicotinamide section.

The reduced form of NAD (sometimes called NADH, NADH2 or NADH/H+) has accepted an electron [cancelling the positive charge], and a hydrogen atom which can be seen on the nicotinamide section. The other hydrogen remains as an H+ ion.

In photosynthesis, hydrogen is transferred using NADP - which has an additional phosphate group attached to the ribose of adenosine..

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Possibly relevant
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Possibly relevant
material available online
(from Amazon.co.uk)