NAD is a coenzyme formed from:
NADP has the same structure with the addition of an extra phosphate group to AMP.
NAD can be reduced to NADH during coupling with reactions which oxidize various organic substrates. For example, the reaction catalyzed by glyceraldehyde phosphate dehydrogenase during glycolysis. NADH then passes to the inside of mitochondria where it donates the electrons it is carrying to the electron transport chain. In this manner, NAD acts as an intermediate energy storage compound that indirectly generates ATP.
Generally, NADP accepts electrons from catabolic reactions to form NADPH. An example is its coupling with the conversion of glucose-6-phosphate to ribose-5-phosphate in the pentose phosphate pathway. NADPH has a slightly different role to NADH in that it does not donate electrons to the electron transport chain. Instead, it tends to reduce intermediates in anabolic pathways e.g. fatty acid synthesis.
Last reviewed 01/2018