Glucose complete oxidation

Respiratory, or oxidative, metaboHsm produces more energy than fermentation. Complete oxidation of one mol of glucose to carbon dioxide and water may produce up to 36 mol ATP in the tricarboxyHc acid (TCA) cycle or related oxidative pathways. More substrates can be respired than fermented, including pentoses (eg, by Candida species), ethanol (eg, by Saccharomjces), methanol (eg, by Hansenu/a species), and alkanes (eg, by Saccharomjces lipoljticd). 

Succinyl-CoA derived from propionyl-CoA can enter the TCA cycle. Oxidation of succinate to oxaloacetate provides a substrate for glucose synthesis. Thus, although the acetate units produced in /3-oxidation cannot be utilized in glu-coneogenesis by animals, the occasional propionate produced from oxidation of odd-carbon fatty acids can be used for sugar synthesis. Alternatively, succinate introduced to the TCA cycle from odd-carbon fatty acid oxidation may be oxidized to COg. However, all of the 4-carbon intermediates in the TCA cycle are regenerated in the cycle and thus should be viewed as catalytic species. Net consumption of succinyl-CoA thus does not occur directly in the TCA cycle. Rather, the succinyl-CoA generated from /3-oxidation of odd-carbon fatty acids must be converted to pyruvate and then to acetyl-CoA (which is completely oxidized in the TCA cycle). To follow this latter route, succinyl-CoA entering the TCA cycle must be first converted to malate in the usual way, and then transported from the mitochondrial matrix to the cytosol, where it is oxida-... 

Glucose is metabolized to pyruvate by the pathway of glycolysis, which can occur anaerobically (in the absence of oxygen), when the end product is lactate. Aerobic tissues metabolize pyruvate to acetyl-CoA, which can enter the citric acid cycle for complete oxidation to CO2 and HjO, linked to the formation of ATP in the process of oxidative phosphorylation (Figure 16-2). Glucose is the major fuel of most tissues. 

The pentose phosphate pathway, present in the cytosol, can account for the complete oxidation of glucose, producing NADPH and COj but not ATP. 

Fats such as palmitic acid are metabolized through pathways similar to the ones for the oxidation of glucose. The complete oxidation of palmitic acid has a standard free energy change of-9790 kJ/mol and produces 130 ATP molecules per molecule of palmitic acid consumed. You should be able to verily that this metabolic process has about the same efficiency as the oxidation of glucose. 

THE COMPLETE OXIDATION OF GLUCOSE REQUIRES TRICARBOXYLIC ACID (TCA) CYCLE ACTIVITY 543... 

Cerebral metabolic rate declines from developmental levels and plateaus after maturation. Reliable quantitative data on the changes in cerebral circulation and metabolism in humans from the middle of the first decade of life to old age have been reported [2,39,44]. By 6 years of age, cerebral blood flow and oxygen consumption already have attained high rates, and they decline thereafter to the rates of normal young adulthood [45]. Oxygen is utilized in the brain almost entirely for the oxidation of carbohydrates [46]. The equation for the complete oxidation of glucose is ... 

The effect which nutrient discharges have on the dissolved oxygen of a stream is best demonstrated by reference to a simple organic molecule. If the total oxidation of glucose to carbon dioxide and water is considered (equation 10.1), one part by weight of glucose would require 1.06 parts of oxygen for complete oxidation. 

Given that the maximum energy liberated from the complete oxidation of glucose to C02 and H20) is 2866kJ/mol and that the molecular weight of glucose is 180... 

These points can be better appreciated by comparing the complete oxidation of glucose with that of a typical saturated fatty acid, palmitate. 

Under aerobic conditions, the pyravate is oxidized to CO and H O via the tricarboxylic acid or Krebs cycle and the electron transport system. The net yield for glycolysis followed by complete oxidation is 38 moles ATP per mole glucose, although there is evidence that the yield for bacteria is 16 moles ATP per mole glucose (Aiba et al., 1973). Thus, 673 kcal are liberated per mole glucose, much of which is stored as ATP. 

The complete oxidation of one molecule of glucose to carbon dioxide and water via glycolysis and the citric acid cycle generates 38 molecules... 

For calculation of rate of ATP generation from glucose, assuming complete oxidation of glucose, multiply rate of glucose utilisation by 30. 

One mole of glucose requires 6 moles of oxygen for complete oxidation, so that the uptake of glucose, on the basis of micromoles per gram tissue per minute, can be calculated from oxygen uptake provided no other fuel is being used. Such data are presented in the last column of (Table 2.8). 

As an example, in glucose metabolism, blood glucose is S, which is the substrate for complete oxidation in several organs, e.g. the brain glucose is provided, via food, from the environment and the products of the pathway, CO2 and H2O, are lost to the environment through the lungs. 

These short-chain fatty acids are acetic, butyric, lactic and propionic acids, also known as volatile fatty acids, VFA. They are produced from fermentation of carbohydrate by microorganisms in the colon and oxidised by colonocytes or hepatocytes (see above and Chapter 4). Butyric acid is activated to produce butyryl-CoA, which is then degraded to acetyl-CoA by P-oxidation acetic acid is converted to acetyl-CoA for complete oxidation. Propionic acid is activated to form propionyl-CoA, which is then converted to succinate (Chapter 8). The fate of the latter is either oxidation or, conversion to glucose, via glu-coneogenesis in the liver. 

Catabolism. This results, eventually, in formation of ammonia and small carbon-contaiiting compounds. The carbon skeletons are used for the synthesis of glucose and triacylglycerol or for complete oxidation to CO2,... 

These processes are, of course, more complex than this details are presented in this and other chapters. In brief, there are three phases for the complete oxidation of glucose and fatty acids ... 

Glycogen complete oxidation (for one glucose molecule-in-glycogen) 31... 

Approximately ten times more ATP is generated from the complete oxidation of one molecule of glncose, compared with the conversion of one molecule of glucose to lactate. A number of calculations demonstrate the difference that this would make in the use of fuels to provide sufficient ATP for various activities ... 

The ATP required by the human brain is obtained from the complete oxidation of glucose it requires about 4 g of glucose per hour. If the same amount of ATP were to be generated from the conversion of glucose to lactate, approximately 60 g per hour would be required (i.e. almost 1.5 kg of glucose each day). 

Table 9.7 Effect of aerobic physical training on the maximum capacity for ATP generation from conversion of glycogen to lactate (glycolysis) and complete oxidation of glucose (the Krebs cycle) in the guadriceps muscle of male and female volunteers...

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