Aerobic metabolism phosphorylation

In any cell that depends on aerobic metabolism, if the rate of ATP utilisation increases, the rate of the Krebs cycle, electron transfer and oxidative phosphorylation must also increase. The mechanism of regulation discussed here is for mammalian skeletal muscle since, to provide sufficient ATP to maintain the maximal power output, at least a 50-fold increase in flux through the cycle is required so that the mechanism is easier to study (Figure 9.22). 

The existence of mitochondrial DNA, ribosomes, and tRNAs supports the hypothesis of the endosymbiotic origin of mitochondria (see Fig. 1-36), which holds that the first organisms capable of aerobic metabolism, including respiration-linked ATP production, were prokaryotes. Primitive eukaryotes that lived anaerobically (by fermentation) acquired the ability to carry out oxidative phosphorylation when they established a symbiotic relationship with bacteria living in their cytosol. After much evolution and the movement of many bacterial genes into the nucleus of the host eukaryote, the endosymbiotic bacteria eventually became mitochondria. 

Optimum living conditions also give rise to intensification of aerobic metabolism. Within the zone of temperature tolerance, the intensification depends directly upon temperature (Van t Hoff-Arrhenius law). Many workers have shown that, in the optimum temperature zone, there are increases in oxygen consumption, activities of cytochrome oxidase and succinic dehyrogenase, respiration/phosphorylation ratio (respiratory control) and muscle electrical potential (Hochachka and Somero, 1973,1977 Wodtke, 1974 Khaskin, 1975 Derkatchev et al., 1976 Walesby and Johnston, 1980 Romanenko etal., 1991). 

SQR (respiratory complex II) is involved in aerobic metabolism as part of the citric acid cycle and of the aerobic respiratory chain (Saraste, 1999). QFR participates in anaerobic respiration with fumarate as the terminal electron acceptor (Kroger, 1978 Kroger etal., 2002) and is part of the electron transport chain catalyzing the oxidation ofvarious donor substrates (e.g., H2 or formate) by fumarate. These reactions are coupled via an electrochemical proton potential (Ap) to ADP phosphorylation with inorganic phosphate by ATP synthase (Mitchell, 1979). 

The first sub-cellular organelle to be isolated (other than the nucleus), mitochondria are the powerhouse of the cell, generating ATP through aerobic oxidative phosphorylation the TCA (Krebs) cycle (the hub of metabolism ) and fatty acid oxidation take place entirely within mitochondria. Other pathways and cycles (urea cycle, haem biosynthesis, cardiohpin synthesis, quinone and steroid biosynthesis) include steps both outside and inside the mitochondria. 

As animals ourselves, we perhaps easily overlook the ultimate primacy of photosynthesis for our biosphere. Photosynthesis is the source of essentially all the carbon compounds and all the oxygen that makes aerobic metabolism possible. Moreover, as we shall see, there are considerable mechanistic and evolutionary parallels between the light reactions of photosynthesis and steps in oxidative phosphorylation. 

Cyanide is described as a cellular toxin because it inhibits aerobic metabolism. It reversibly binds with ferric (Fe " ") iron-containing cytochrome oxidase and inhibits the last step of mitochondrial oxidative phosphorylation. This inhibition halts carbohydrate metabolism from citric acid cycle, and intracellular concentrations of adenosine triphosphate are rapidly depleted. When absorbed in high enough doses, respiratory arrest quickly ensues, which is probably caused by respiratory muscle failure. Cardiac arrest and death inevitably follow. 

Aerobic Metabolism II Electron Transport and Oxidative Phosphorylation... 

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