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Chapter Four: Cell Nutrition and Respiration
Through aerobic respiration, the glucose molecule is thoroughly broken down, and a great amount of energy is used to form ATP molecules. To calculate the net gain in ATP of aerobic respiration, we must return all the way back to the first stage which we discussed: glycolysis.
Two molecules of ATP were required to begin the reaction of glycolysis, but four were produced as a result. Therefore, there was a net gain of two ATP molecules. Also, glycolysis resulted in the formation of two molecules of NADH, each of which provides the energy for the formation of three molecules of ATP through the electron transport chain. Therefore, the two NADH molecules produce six ATP molecules total. So, the total number of ATP molecules formed from glycolysis is eight.
When each molecule of pyruvic acid is oxidized, one molecule of NADH is produced. This occurs twice, since one glucose molecule splits into two molecules of pyruvic acid. Therefore, two molecules of NADH are produced, each of which results in the formation of three molecules of ATP, for a total of six molecules of ATP.
As mentioned in the section on the Krebs cycle, two molecules of ATP, six of NADH, and two of FADH2 are formed from the breakdown of one glucose molecule, since the Krebs cycle occurs twice for each glucose molecule. The six NADH molecules result in the production of eighteen ATP molecules, and the two molecules of FADH2 produce four ATP molecules, for a total of 22. The total is therefore the two ATP molecules produced directly plus the 22 molecules formed through the electron transport chain, which equals 24.
Adding together the 8 ATP molecules formed during glycolysis, the 6 from the oxidation of pyruvic acid, and the 24 from the Krebs cycle, we obtain a final net total of 38 molecules of ATP formed for each molecule of glucose.