NAD. Computer artwork of a molecule of nicotinamide adenine dinucleotide (NAD). It is an extremely important coenzyme found in nature. Its function is to assist in many important biological reactions, including those involved in respiration in the cell. It does this by accepting and carrying electrons, This is vital if the biological reactions are to proceed. The chemical formula of NAD is C21.H27.N7.O14.P2. The atoms are shown as cylinders and are colour-coded: carbon (yellow), oxygen (red), nitrogen (blue), hydrogen (white) and phosphorus (green).