Glucose energy yield

As an example of two reactions that are coupled, look at the phosphorylation reaction of glucose to yield glucose 6-phosphate plus water, an important step in the breakdown of dietary carbohydrates. The reaction of glucose with HOPO 2- does not occur spontaneously because it is energetically unfavorable, with AG° = + 13.8 kj/mol. (The standard free-energy change for a biological reaction is denoted AG0 and refers to a process in which reactants and products have a concentration of 1.0 M in a soiution with pH = 7.)... 

The energy yield from glycolysis for the anaerobic decomposition of glucose to 2 mol of lactic acid may be calculated as follows ... 

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

It is instructive to compare the energy yield from three molecules of glucose (Cig) with that from one molecule of stearic acid (also Cig). 

The energy yield resulting from glucose metabolism under aerobic conditions includes... 

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... 

The details of the process and the oxidation-reduction balance can be pictured as in Eq. 17-25. Pyruvate is cleaved by the pyruvate formate-lyase reaction (Eq. 15-37) to acetyl-CoA and formic acid. Half of the acetyl-CoA is cleaved to acetate via acetyl-P with generation of ATP, while the other half is reduced in two steps to ethanol using the two molecules of NADH produced in the initial oxidation of triose phosphate (Eq. 17-25). The overall energy yield is three molecules of ATP per glucose. The "efficiency" is thus (3 x 34.5)... 

In order for the cell to carry out a controlled oxidation of D-glucose and conserve some of the energy derived from the process, it is lira necessary to add phosphate to the hexose with the expenditure of energy. The necessary energy and the phosphate per se is supplied by ATP in two separate reactions of the system. Since each molecule of glucose can yield two molecules of irioxe phosphate for oxidation, the conversion of glucose in pyruvic acid nets two molecules of ATP per molecule of hexose utilized. 

Since two molecules of ATP are converted to ADP in the first part of the glycolysis process, there is a net gain of two molecules of ATP. The second part of the glycolysis process also yields two molecules of NADH + H+ per molecule of glucose. Subsequently, the energy-yielding conversion of the two molecules of ATP back to ADP and the oxidation of NADH,... 

Two ATP equivalents were used to activate the fatty acid, leading to a total energy yield of 129 ATPs, over three times the amount of energy obtained from metabolizing a single molecule of glucose. 

In experimental stroke, the zone of dense ischemia leads to the rapid exhaustion of substrates, particularly oxygen and glucose. The impaired energy yield cannot maintain the ion pumps so that cells loose their membrane potential (anoxic depolarization of glia and neurons). As a consequence, volt-... 

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