Aerobic metabolism respiration

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. 

Substances in the bulk solution diffuse into the biofilm, where they are consumed (such as oxygen, point 1 in Figure 6) or recycled (such as sulfate through stepwise reoxidation of H2S from sulfate reduction, point 5). Within the biofilm, very steep gradients exist for oxygen or hydrogen sulfide and also for ferrous iron from reductive dissolution of ferric oxides. These gradients result from the coexistence of anaerobic and aerobic metabolisms such as aerobic respiration (point 1), reduction of ferric oxides (point 3), and sulfate... 

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). 

Krebs cycle The second metabolic pathway in aerobic cell respiration converts carbohydrates and lipids (sugars and fats) into carbon dioxide and water and produces energy-rich compounds, including some ATP. 

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). 

A common approach to estimating the contribution of microorganisms to Fe(III) and Mn(IV) reduction based on carbon mass balance. Total anaerobic microbial respiration is estimated by measuring the carbon mineralization rate (i.e., Y.CO2 + CH4 production). The carbon that was respired by SO -reducing bacteria and methanogens is subtracted from the total, and the difference is assumed to be the contribution of Fe(III)- and Mn(IV)-reducing bacteria (Canfield et al., 1993b Thamdmp, 2000). Typically, the contribution of aerobic metabolism to carbon... 

Reducing the 02 concentration around fresh fruits and vegetables reduces their respiration rate to an extent that varies with temperature, commodity, cultivar, and physiological age at harvest. Below a minimum of about 1 to 2% 02, a shift from aerobic to anaerobic respiration occurs with a concomitant increase in CO2 production Q0). The reduction in aerobic metabolism associated with reduced 02 levels is apparently not mediated by cytochrome oxidase, which has a K , value of 10"8 to 10 7 M 02 (11.12). It is more likely that reduction of aerobic respiration results from diminished activity of other oxidases such as ascorbic acid oxidase, polyphenol oxidase (FFO), and glycolic acid oxidase, whose affinities for 02 are 5 to 6 times lower than that of cytochrome oxidase (12). 

However, as distinguished from the aerobic metabolism of normal cells, cancer cell metabolism is in the main anaerobic and does not invoke the carboxylic acid cycle, dependent on oxygen and fimdamental to cell respiration, as set forth in Chapter 3 for glycolysis. Thus, respiration of the cancerous cell is excluded from consideration. Hence, from this standpoint, the anticancer claims for amygdalin or laetrile can be viewed as missing the mark. That is, under this interpretation, cyanide would affect aerobic normal cells but not anaerobic cancerous cells. 

The dissolved oxygen half saturation constant (Ks) for microbial respiration has been reported to be less than 0.1 mg/1. It was found to be related to cell size for many organisms tested. Aerobic metabolic activities should therefore proceed at maximum rates when the dissolved oxygen concentration is... 

The phase of primary respiratory alkalosis rarely is recognized in children with salicylate toxicity. They usually present in a state of mixed respiratory and renal acidosis, characterized by a decrease in blood pH, a low plasma bicarbonate concentration, and normal or nearly normal plasma PCO2. Direct salicylate-induced depression of respiration prevents adequate respiratory hyperventilation to match the increased peripheral production of CO2- Consequently, plasma PCO2 increases and blood pH decreases. Because the concentration of bicarbonate in plasma already is low due to increased renal bicarbonate excretion, the acid-base status at this stage essentially is an uncompensated respiratory acidosis. Superimposed, however, is a true metabolic acidosis caused by accumulation of acids as a result of three processes. First, toxic concentrations of salicylates displace 2-3 mEq/L of plasma bicarbonate. Second, vasomotor depression caused by toxic doses of salicylates impairs renal function, with consequent accumulation of sulfuric and phosphoric acids. Third, salicylates in toxic doses may decrease aerobic metabolism as a result of inhibition of various enzymes. This derangement of carbohydrate metabolism leads to the accumulation of organic acids, especially pyruvic, lactic, and acetoacetic acids. 

Alcoholic fermentation is less efficient in producing ATP than aerobic root respiration thus, net energy production by the anaerobic pathway is only a fraction of that produced by the aerobic respiration. Root energy metabolism under aerobic and anaerobic conditions is as follows ... 

One of the most important functions of the microcirculation is the delivery of O2 to tissue and the removal of waste products, particularly of CO2, from tissue. O2 is required for aerobic intracellular respiration for the production of adenosine triphosphate (ATP). C02is produced as a by-product of these biochemical reactions. Tissue metabolic rate can change drastically, for example, in aerobic muscle in the transition... 

The early work of Meyerhof showed that there was an intimate connection between resynthesis of carbohydrate and aerobic metabolism. When the production of lactic acid by tissues under anaerobic conditions was compared with the production of lactic acid under aerobic conditions, it was found that the uptake of 1 mole of respired oxygen inhibited the formation of 1 to 2 moles of lactic acid i.e., three to six times as much lactic acid as could have been oxidized by the observed oxygen uptake. This phenomenon of the suppression of glycolysis under aerobiosis has been called by Warburg the Pasteur effect. 

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