Electron transport chain organization

The ready reversibility of this reaction is essential to the role that qumones play in cellular respiration the process by which an organism uses molecular oxygen to convert Its food to carbon dioxide water and energy Electrons are not transferred directly from the substrate molecule to oxygen but instead are transferred by way of an electron trans port chain involving a succession of oxidation-reduction reactions A key component of this electron transport chain is the substance known as ubiquinone or coenzyme Q... 

The decline in immune function may pardy depend on a deficiency of coenzyme Q, a group of closely related quinone compounds (ubiquinones) that participate in the mitochondrial electron transport chain (49). Concentrations of coenzyme Q (specifically coenzyme Q q) appear to decline with age in several organs, most notably the thymus. 

These energy-producing reactions are termed respiration processes. They require the presence of an external compound that can serve as the terminal electron acceptor of the electron transport chain. However, under anaerobic conditions, fermentation processes that do not require the participation of an external electron acceptor can also proceed. In this case, the organic substrate undergoes a balanced series of oxidative and reductive reactions, i.e., organic matter reduced in one step of the process is oxidized in another. 

All tissues except mature red blood cells are able to manufacture haem for use in the respiratory cytochrome proteins of the electron transport chain. However, the liver is an especially important site of haem synthesis because it (a) is a major organ of erythropoiesis in utero and (b) haem-containing cytochrome-P450 (CYP-450) enzymes play significant roles in hepatic detoxification of drugs, toxins and endogenous waste products (Section 6.4). 

Marine organisms concentrate metals in their tissues and skeletal materials. Many of these trace metals are classified as micronutrients because they are required, albeit in small amounts, for essential metabolic functions. Some are listed in Table 11.4, illustrating the role of metals in the enzyme systems involved in glycolysis, the tricarboxylic acid cycle, the electron-transport chain, photosynthesis, and protein metabolism. These micronutrients are also referred to as essential metals and, as discussed later, have the potential to be biolimiting. 

Electron transport chain a series of multienzyme complexes organized in the inner layer of the mitochondrial membrane that catalyze the transport of electrons from reduced coenzymes to molecular oxygen coupled to the synthesis of ATP. 

The electron transport chain is vital to aerobic organisms. Interference with its action may be life threatening. Thus, cyanide and carbon monoxide bind to haem groups and inhibit the action of the enzyme cytochrome c oxidase, a protein complex that is effectively responsible for the terminal part of the electron transport sequence and the reduction of oxygen to water. 

What has been achieved by the participation of coenzyme systems and the electron transport chain is twofold. First, there is no need for the substrate AH2 to react with oxygen. Second, it provides common routes for the oxidation of many different organic compounds, rather than a specific route for every compound, a vast variety of which will be present in... 

Generalized/organ specific (lung disease, anemia, decreased blood supply) Cellular hypoxia (cyanide poisoning of electron transport chain in mitochondria) Inflammatory (pathology from abnormal inflammatory response in the body) Autoimmune and/or chronic diseases (systemic lupus erythmatosus, rheumatoid arthritis)... 

Figure 18-5 A current concept of the electron transport chain of mitochondria. Complexes I, III, and IV pass electrons from NADH or NADPH to 02, one NADH or two electrons reducing one O to HzO. This electron transport is coupled to the transfer of about 12 H+ from the mitochondrial matrix to the intermembrane space. These protons flow back into the matrix through ATP synthase (V), four H+ driving the synthesis of one ATP. Succinate, fatty acyl-CoA molecules, and other substrates are oxidized via complex II and similar complexes that reduce ubiquinone Q, the reduced form QH2 carrying electrons to complex III. In some tissues of some organisms, glycerol phosphate is dehydrogenated by a complex that is accessible from the intermembrane space.

Chemolithotrophic organisms often grow slowly, making study of their metabolism difficult.310 Nevertheless, these bacteria usually use electron transport chains similar to those of mitochondria. ATP is formed by oxidative phosphorylation, the amount formed per electron pair depending upon the number of proton-pumping sites in the chain. This, in turn, depends upon the electrode potentials of the reactions involved. For example, H2, when oxidized by 02, leads to passage of electrons through the entire electron transport chain with synthesis of 3 molecules of ATP per electron pair. On the other hand, oxidation by 02 of nitrite, for which E° (pH 7) = +0.42 V, can make use only of the site III part of the chain. Not only is the yield of ATP less than in the oxidation of H2 but also there is another problem. Whereas reduced pyridine... 

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