Aerobic respiration electron transport chain

In the case of fermentation, the carbon and energy source is broken down by a series of enzyme-mediated reactions that do not involve an electron transport chain. In aerobic respiration, the carbon and energy source is broken down by a series of enzyme-mediated reactions in which oxygen serves as an external electron acceptor. In anaerobic respiration, the carbon and energy source is broken down by a series of enzyme-mediated reactions in which sulfates, nitrates, and carbon dioxide serve... 

Coenzyme QIO (21) is one of the essential enzymes in the mitochondrial electron transport chain, participating in the aerobic respiration cycle. The role of Co-QlO as a cardioprotective substance and an antioxidant are well studied. Recently, it was found that Co-QlO is also capable of attenuating the intracellular deposition of Ap in transgenic AD mouse models. Additionally, the same group reported that Co-QlO administration also led to reduction of preexisting plaque burden in the same model. Such properties are suggestive of a potential therapeutic role for Co-QlO in AD. 

In this chapter we will look at the processes by which reduced carriers such as NADH and FADH2 are oxidized within cells. Most familiar to us, because it is used in the human body, is aerobic respiration. Hydrogen atoms of NADH, FADH2, and other reduced carriers appear to be transferred through a chain of additional carriers of increasingly positive reduction potential and are finally combined with 02 to form H20. In fact, the hydrogen nuclei move freely as protons (or sometimes as H ions) it is the electrons that are deliberately transferred. For this reason, the chain of carriers is often called the electron transport chain. It is also referred to as the respiratory chain. 

Electron transport chain A series of reactions that takes place within the mitochondria that result in the production of ATP. It is a major process of aerobic respiration. 

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). 

Aerobic respiration The mitochondrial electron-transport chain incorporates cytochrome c, and the oxidation and reduction of the iron atoms in this biomolecule passes electrons through a series or chain of metabolic reactions. This is illustrated in Figure 4.3. 

Bimetallic catalysis also plays a vital role in the four-electron reduction of dioxygen to water, which is the reverse process of photosynthesis, to maintain the life of an aerobic organism by the respiration (3,157,158). Cytochrome c oxidases (CcOs), the last protein in the electron transport chain, are responsible for catalyzing the reduction of dioxygen to water by the soluble electron carrier, cytochrome c(3,157,158). The X-ray structures of CcOs revealed that the catalytic... 

There are many examples of biological oxidation-reduction reactions. For example, the electron-transport chain of aerobic respiration involves the reversible oxidation and reduction of iron atoms in cytochrome c. 

In skeletal muscle and other tissues, ATP is generated by anaerobic glycolysis when the rate of aerobic respiration is inadequate to meet the rate of ATP utilization. Under these circumstances, the rate of pyruvate production exceeds the cell s capacity to oxidize NADH in the electron transport chain, and hence, to oxidize pyruvate in the TCA cycle. The excess pyruvate is reduced to lactate. Because lactate is an acid, its accumulation affects the muscle and causes pain and swelling. 

FIGURE 9.2. Example of a bacterial electron transport chain Postulated mechanism for proton translocation in Escherichia coli during aerobic respiration. (Adapted from Ref. 3.)... 

Aerobic respiration can be subdivided into a number of distinct but coupled processes, such as the carbon flow pathways resulting in the production of carbon dioxide and the oxidation of NADH + H+ and FADH2 (flavin adenine dinucleotide) to water via the electron transport systems or the respiratory chain. 

There are two fermentative processes that at first appear to be quite similar to oxygen and nitrate-dependent respirations the reduction of C02 to methane and of sulfate to sulfide. However, on closer examination, it is clear that they bear little resemblance to the process of denitrification. In the first place, the reduction of C02 and of sulfate is carried out by strict anaerobes, whereas nitrate reduction is carried out by aerobes only if oxygen is unavailable. Equally important, nitrate respirers contain a true respiratory chain sulfate and C02 reducers do not. Furthermore, the energetics of these processes are very different. Whereas the free energy changes of 02 and nitrate reduction are about the same, the values are much lower for C02 and sulfate reduction. In fact, the values are so low that the formation of one ATP per H2 or NADH oxidized cannot be expected. Consequently, not all the reduction steps in methane and sulfide formation can be coupled to ATP synthesis. Only the reduction of one or two intermediates may yield ATP by electron transport phosphorylation, and the ATP gain is therefore small, as is typical of fermentative reactions. 

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