Glucose anaerobic catabolism

Anaerobic catabolic reactions are similar, although the electron acceptor isn t oxygen. The next example shows the fermentation of glucose to lactic acid. 

Figure 19-1 a Normal and ischemic myocardial metabolism of glucose. A total production of 36 moles of ATP results from the aerobic catabolism of 1 mole of glucose and use of NADH and FADH. in the oxidative phosphorylation process in mitochondria. When oxygen is not available, NADH and FADH levels rise and shut off the tricarboxylic acid (TCA) cycle. Pyruvate is converted to lactate. Only 2 moles of ATP are formed from anaerobic catabolism of 1 mole of glucose. (Adapted from Giuliani, E. R., ei al. Cardiology Fundamentals and Practice, 2nd ed. By permission of the Mayo Foundation, Rochester, MN.)... 

The net yield of ATP from the anaerobic catabolism of glucose can be calculated as shown in Table 11.3. Glycolysis yields two molecules of ATP per molecule of glucose consumed. 

The cost of biomass synthesis is easily determined in anaerobic cultures since oxidative phosphorylation is not active. The only ATP synthesis step is ethanol formation from pyruvate, and glycerol synthesis consumes one mole of ATP per mole formed. The ATP yield of anaerobic catabolic reactions is low as shown in Table 21. In fact, degradation of glucose is incomplete and the... 

Glycolysis is a catabolic pathway in the cytoplasm that is found in almost all organisms— irrespective of whether they live aerobically or anaerobically. The balance of glycolysis is simple glucose is broken down into two molecules of pyruvate, and in addition two molecules of ATP and two of NADH+H"" are formed. 

Since more ATP is produced by respiration of glucose than by fermentation, and since the ATP requirement for biosynthesis of cell mass is the same, it follows that to obtain the same cell yield from glucose, the yeast should consume less sugar under aerobic conditions than under anaerobic conditions, with a resultant decrease in glycolytic flux (Berry, 1982). These phenomena are referred to as the Pasteur effect. Although this effect is observed in some yeasts, in S. cerevisiae it is either absent (Gancedo and Serrano, 1989) or observed only under certain nutrient-limited conditions. The main reason for the absence of the Pasteur effect is that even under aerobic conditions, fermentation is still the main catabolic route for the utilisation of glucose because of the Crabtree effect (Walker, 1994). The Crabtree effect is the repression... 

Oxidative phosphorylation produces most of the ATP made in aerobic cells. Complete oxidation of a molecule of glucose to C02 yields 30 or 32 ATP (Table 19-5). By comparison, glycolysis under anaerobic conditions (lactate fermentation) yields only 2 ATP per glucose. Clearly, the evolution of oxidative phosphorylation provided a tremendous increase in the energy efficiency of catabolism. Complete oxidation to C02 of the coenzyme A derivative of palmitate (16 0), which also occurs in the mitochondrial matrix, yields 108 ATP per palmitoyl-... 

Only a small fraction of the total free energy content of glucose is released under anaerobic conditions. This is because no net oxidation of organic substrates can occur in the absence of oxygen. Catabolism under anaerobic conditions means that every oxidative event in which electrons are removed from an organic compound must be accompanied... 

In fast white fibers, glycolysis catabolizes glucose. The relative lack of mitochondria in these fibers causes the white appearance. The rapid breakdown of glucose by anaerobic metabolism means that ATP is made rapidly. These muscles are used in rapid, short-duration movement and exhibit a fast twitch when electrically stimulated. The flight muscles of birds are of this type—remember that you find the white meat of a chicken on the breast. 

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