NAD and reduced NAD molecules - rotatable in 3 dimensions

NAD Notes on these diagrams reduced NAD

The basic form of the molecule carries a positive charge (so it may be callled NAD+) due to the arrangement of bonds on one of the nitrogen atoms (labelled with a +) in the nicotinamide section.
NAD (Nicotinamide Adenine Dinucleotide) is a hydrogen acceptor, used in respiration to transfer (pairs of) hydrogen atoms to other molecules. Dehydrogenation - the removal of hydrogen - is effectively a form of oxidation.

NAD consists of 2 nucleotides, joined by their phosphate groups (orange). 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 - adenine - and at the other end is a slightly simpler single ring structure - nicotinamide.

In photosynthesis, hydrogen is transferred using NADP - which has an additional phosphate group [position marked here with (P)].

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Colours explained

The reduced form of NAD (sometimes called NADH, NADH2 or NADH/H+) accepts a hydrogen atom (labelled H in the diagram above) on the nicotinamide section, and the other hydrogen remains as an H+ ion.

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