Energy during glucose oxidation

These electrons are subsequently transferred to cytochrome h, and then to the terminal electron acceptor, Fe oxide in contact with the cell membrane. This reaction is mediated by the enzyme Fe reductase. The net amount of energy released during glucose oxidation using Mn(IV) and Fe(III) is approximately 67 and 15%, respectively, of that released from glucose breakdown stored in the reduced end products such as Mn(II) and Fe(II). Reduction of Mn oxides occurs in wetland soils with Eh range of +200 to +300 mV, as compared to -100 to +100 mV for Fe oxide reduction. 

Recall that during respiration, animals gain energy from glucose by oxidizing it—that is, by transferring... 

During normal activity, a person uses the equivalent of about 10 MJ of energy a day. Assume that this value represents AG, and estimate the average current through your body in the course of a day, assuming that all the energy that we use arises from the reduction of 02 in the glucose oxidation reaction. See Box 12.1. 

This value of 20 kJ/L O2 can be very useful for example, it can be used to calculate that a top-class marathon runner requires oxidation of 5 g of carbohydrate every minute during the race, provided that no other fuel is used. The athlete takes up 4 litres of oxygen each minute, which is equivalent to 4 x 20, or 80 kJ each minute as 1 g of glucose releases 16 kJ of energy, the glucose or glycogen used is 80/16 or 5 g each minute. 

Fuel Oxidation. During fasting, glucose continues to be oxidized by glucose-dependent tissues such as the brain and red blood cells, and fatty acids are oxidized by tissues such as muscle and liver. Muscle and most other tissues oxidize fatty acids completely to CO2 and H2O. However, the liver partially oxidizes fatty acids to smaller molecules called ketone bodies, which are released into the blood. Muscle, kidney, and certain other tissues derive energy from completely oxidizing ketone bodies in the tricarboxylic acid (TCA) cycle. 

Fig. 13-16 Inhibition of glucose oxidation in the brain during dependence on ketone bodies for energy.

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