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FAD is an aromatic ring system, whereas FADH 2 is not. [12] This means that FADH 2 is significantly higher in energy, without the stabilization through resonance that the aromatic structure provides. FADH 2 is an energy-carrying molecule, because, once oxidized it regains aromaticity and releases the energy represented by this stabilization ...
Found in all living cells, NAD is called a dinucleotide because it consists of two nucleotides joined through their phosphate groups. One nucleotide contains an adenine nucleobase and the other, nicotinamide. NAD exists in two forms: an oxidized and reduced form, abbreviated as NAD + and NADH (H for hydrogen), respectively.
The net gain from one cycle is 3 NADH and 1 FADH 2 as hydrogen (proton plus electron) carrying compounds and 1 high-energy GTP, which may subsequently be used to produce ATP. Thus, the total yield from 1 glucose molecule (2 pyruvate molecules) is 6 NADH, 2 FADH 2, and 2 ATP. [12] [13] [8]: 90–91
Products of the first turn of the cycle are one GTP (or ATP), three NADH, one FADH 2 and two CO 2. Because two acetyl-CoA molecules are produced from each glucose molecule, two cycles are required per glucose molecule. Therefore, at the end of two cycles, the products are: two GTP, six NADH, two FADH 2, and four CO 2. [18]
In eukaryotes, NADH is the most important electron donor. The associated electron transport chain is NADH → Complex I → Q → Complex III → cytochrome c → Complex IV → O 2 where Complexes I, III and IV are proton pumps, while Q and cytochrome c are mobile electron carriers. The electron acceptor for this process is molecular oxygen.
Acetyl-CoA enters the citric acid cycle, generating NADH and FADH 2, which are electron carriers used in the electron transport chain. It is named as such because the beta carbon of the fatty acid chain undergoes oxidation and is converted to a carbonyl group to start the cycle all over again.
The energy stored in the chemical bonds of glucose is released by the cell in the citric acid cycle, producing carbon dioxide and the energetic electron donors NADH and FADH. Oxidative phosphorylation uses these molecules and O 2 to produce ATP , which is used throughout the cell whenever energy is needed.
The energy from the acetyl group, in the form of electrons, is used to reduce NAD+ and FAD to NADH and FADH 2, respectively. NADH and FADH 2 contain the stored energy harnessed from the initial glucose molecule and is used in the electron transport chain where the bulk of the ATP is produced. [1]