NAD stands for Nicotinamide Adenine Di-nucleotide, the structure of which is shown below. On the left is NAD, and then on the right is NAD in its reduced form NADH2.
For NAD (or FAD) to be reduced (gain a hydrogen) it must be associated with a dehydrogenase enzyme, as the name suggests it removes the hydrogen from other molecules, it then splits the hydrogen into an electron and a hydrogen ion which are taken up by the NAD or FAD. The diagram below shows FAD (Flavine Adenine di-nucleotide), on the left, and on the right shows FAD after being reduced.
Redox reactions are those where products become either oxidised or reduced; oxidation is the loss of electrons, and reduction is the gain of electrons, it is remembered as OIL RIG as shown below:
OXIDATION
IS
LOSS
REDUCTION
IS
GAIN
Oxidation reactions may involve the removal of hydrogen or the addition of oxygen, this is so, because of the positive and negative charges on the molecules. Oxidation is loss of electrons, so therefore hydrogen has a positive charge and oxygen had a negative charge.
Reduction reactions involve the gaining of electrons, this can be done through the addition of hydrogen or the removal of oxygen, the opposite of oxidation.
When NAD and FAD pick up hydrogen they are reduced, NAD gaining 2 electrons and a Proton, and FAD gaining 2 protons and 2 electrons. As they gain electrons they also gain; this means that when they move down the electron transport chain in respiration, the extra electrons go on to form ATP in the following way. The proteins in the electron transport chain accept an electron (reduction is gain) and so becomes reduced, and then lose it again (oxidation is loss), and become oxidised, energy from the electron is lost at each transfer powering active transport of hydrogen ions across the inner mitochondrial membrane. The result of this is there are more hydrogen ions in the outer mitochondrial space than in the inner mitochondrial space. An equilibrium tries to form between the inner and outer mitochondrial space by diffusion of Hydrogen ions from the high concentration in the outer compartment to the lower concentration in the inner compartment. As these hydrogen ions move through the middle of the stalked granules which hold the ATPase, enzymes that generate ATP, enough energy is released to form new molecules of ATP. The more electrons that can make the energy to start active transport of H+, the more ATP can be produced.
So in summary the structure of NAD is slightly less complicated than FAD, but they are both co-enzymes, which bond loosely with a dehydrogenase enzyme, to remove the hydrogen from other substances and bond to the co-enzyme in a reduction reaction. The structure of the NAD and FAD change slightly as they are reduced this happens when they collect Hydrogen which is produced in respiration, and then when the hydrogen is released into the electron transfer chain the NAD or FAD becomes oxidised. The process of reducing and oxidising these co-enzymes produce a specific amount of energy, which in turn goes on to produce energy in the form of ATP. These co-enzymes are very important molecules within organisms because without them, a lack of energy would be processed, this is why it is important to keep up the vitamin intakes as NAD is synthesised from B3 – nicotinic acid, and FAD is synthesised from B2 – riboflavin.
