Energy Yields from Oxidative Phosphorylation

Energy Yields from Oxidative Phosphorylation (Reactions)... 

By combining the glycolytic pathway, the Krebs cycle, and oxidative phosphorylation, the energy yield from the aerobic degradation of glucose will be... 

We saw in Chapter 14 that the energy yield from the production of two molecules of pyruvate from one molecule of glucose in glycolysis is 2 ATP and 2 NADH. In oxidative phosphorylation (Chapter 19), passage of two electrons from NADH to 02 drives the formation of about 2.5 ATP, and passage of two electrons from FADH2 to 02 yields about 1.5 ATP. This stoichiometry allows us to calculate the overall yield of ATP from the complete... 

What is the energy yield from the complete degradation of butyryl CoA via p-oxidation, the citric acid cycle, and oxidative phosphorylation ... 

The main drawback of the glycerol-3-phosphate shuttle is that only two ATP are produced for each cytoplasmic NADH. The reason is that the electrons are shuttled to FADHj, which )delds only two ATP by oxidative phosphorylation. (The energy yield of the oxidation of mitochondrial NADH is three ATP.) Thus the total energy yield from glycolysis imder aerobic conditions in muscle and nerve cells is two ATP, produced by substrate level phosphorylation, plus four ATP (two ATP per NADH), produced by oxidative phosphorylation. This provides an energy yield of six ATP per glucose. 

Otto Shape had difficulty losing weight because human fuel utilization is too efficient. His adipose tissue fatty acids are being converted to acetyl CoA, which is being oxidized in the TCA cycle, thereby generating NADH and FAD(2H). The energy in these compounds is used for ATP synthesis from oxidative phosphorylation. If his fuel utilization were less efficient and his ATP yield were lower, he would have to oxidize much greater amounts of fat to get the ATP he needs for exercise. 

Energy from fuel oxidation is converted to the high-energy phosphate bonds of adenosine triphosphate (ATP) by the process of oxidative phosphorylation. Most of the energy from oxidation of fuels in the TCA cycle and other pathways is conserved in the form of the reduced electron-accepting coenzymes, NADH and FAD(2H). The electron transport chain oxidizes NADH and FAD(2H), and donates the electrons to O2, which is reduced to H2O (Fig. 21.1). Energy from reduction 0/O2 is used for phosphorylation of adenosine diphosphate (ADP) to ATP by ATP synthase (FgFjATPase). The net yield of oxidative phosphorylation is approximately 2.5 moles of ATP per mole of NADH oxidized, or 1.5 moles of ATP per mole of FAD(2H) oxidized. 

In the second stage of fatty acid oxidation, the acetyl-CoA is oxidized to C02 in the citric acid cycle. A large fraction of the theoretical yield of free energy from fatty acid oxidation is recovered as ATP by oxidative phosphorylation, the final stage of the oxidative pathway. 

Two ATPs are used in glycolysis and four ATPs are synthesized for each molecule of glucose so that the net yield is two ATPs per glucose. Under aerobic conditions, the two NADH molecules arising from glycolysis also yield energy via oxidative phosphorylation. 

Answer Lactate and alanine are converted to pyruvate by their respective dehydrogenases, lactate dehydrogenase and alanine dehydrogenase, producing pyruvate and NADH + H+ and, in the case of alanine, NH. Complete oxidation of 1 mol of pyruvate to C02 and H20 produces 12.5 mol of ATP via the citric acid cycle and oxidative phosphorylation (see Table 16-1). In addition, the NADH from each dehydrogenase reaction produces 2.5 mol of ATP per mole of NADH reoxidized. Thus oxidation produces 15 mol of ATP per mole of lactate. Urea formation uses the equivalent of 4 mol of ATP per mole of urea formed (Fig. 18-10), or 2 mol of ATP per mol of NH4. Subtracting this value from the energy yield of alanine results in 13 mol of ATP per mole of alanine oxidized. 

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