Starting with electron carrying molecules such as NADH and FADH, the \"net\" ATP

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In eukaryotic cell with mitochondria, the majority of ATP is generated from via oxidative phosphorylation, the by a series of redox reactions that transfer electrons from electron carriers with more negative reduction potentials to those with more positive potential. Starting with NADH and ending with the final electron acceptor O2. Because the difference in reduction potentials between NADH and O2 is quite large (about 1.4 volts), the cell is brakes down the energy release in to small steps by the process of electron transport, to harness the most energy as possible. Through out the process protons are transported into the intermembrane space creating a proton gradient that then drives the engine like enzyme, ATP Synthase, by proton motive force. The amount of ATP produced is directly related to the number of protons transported into the intermembrane space or by the number of electrons transported to proton expulsion protien complexes by each oxidative step. For each NADH molecule it is thought that 10 protons are moved across the membrane (NADH = 10 H+) and For each FADH2 it is thought the 6 electrons dontated to the carries translates to a net 6 protons moved in to the intermembrane space (FADH2 = 6 H+) In the process of APT synthesis by ATP Synthase 4 protons are consmed, 3 are used by the enzyme and 1 is used for transport of ATP (ADP + P --> ATP). Thus: 1 NADH = 2.5 ATP 1 FADH2 = 1.5 ATP So, if up to 10 NADH (2 from glycolysis; 2 from pyruvate conversion ot acetyl CoA; and 6 from the 2 turns of the TCA cycle (also knows as Krebbs)) and 2 FADH2 ( from the 2 turns of the TCA cycle) are produced by glucose is completly oxidized to 6 CO2 : 10 NADH = 25 ATP 2 FADH2 = 3 ATP Because the energy utilized durring the ETC is produced via spontanious redox reaction and proton motive force, there is not ATP consuption like there is in glycolysis and the Krebbs Cycle (TCA). Thus the net gain of ATP from the ETC (oxidative phosphylation) is 28. *** Note many text round the ATP:NADH and ATP:FADH2 ratios up to 3:1 and 2:1 respectively... This results in a much larger number, 34. Also when calculating the total net ATP produced from glucose catabolism you need to take in to account the use of ATP as an energy source and the number of times the cycle occurs as in the glycolytic pathway and the TCA cycle. glycolysis yields a total of 4 ATP but uses 2 ATP in the process so the net gain is only 2 ATP TCA cycle yields 1 ATP for each turn, but goes through 2 cycles for each glucose molecule so the net yield is 2 ATP Thus, sum of all the reactions in Aerobic Respiration yields 32 ATP (or if you are rounding up as some text do, 38 ATP) These numbers are for eukaryotic ATP production, the numbers and cycles utilized can be different for prokaryotes. I hope this helps!

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