Oxidative phosphorylation electron transfer

Oxidative Phosphorylation Electron transfer through the cytochrome system liberating free energy which is transformed into high-energy phosphate bonds. [NIH]... 

A similar inconsistency exists concerning oxidative phosphorylation in AD. Although activities of enzymes of the mitochondrial electron transfer chain are reported to be normal in AD brain, partial uncoupling of oxidative phosphorylation (electron transfer and phosphorylation of adenosine diphosphate are normally functionally linked) (Sims et al., 1987) and overexpression of cytochrome oxidase subunit-3 gene in cerebral temporal cortices (Alberts et al., 1992) have been reported. In addition, substantial decreases of complex IV activity were detected in platelets from five patients with AD (Parker et al., 1990). 

Structural problems in oxidative phosphorylation Electron transfer... 

We saw in Case studies 4.2 and 4.3 that exergonic electron transfer processes drive the synthesis of ATP in the mitochondrion during oxidative phosphorylation. Electron transfer between protein-bound co-factors or between proteins also plays a role in other biological processes, such as photosynthesis (Section 5.11 and Case study 12.3), nitrogen fixation, the reduction of atmospheric Nj to NH3 by certain microorganisms, and the mechcuiisms of action of oxidoreductcises, which are enzymes that catalyze redox reactions. 

Figure 19.25. Comparison of Photosynthesis and Oxidative Phosphorylation. The light-induced electron transfer in photosynthesis drives protons into the thylakoid lumen. The excess protons flow out of the lumen through ATP synthase to generate ATP in the stroma. In oxidative phosphorylation, electron flow down the electron-transport chain pumps protons out of the mitochondrial matrix. Excess protons from the intermembrane space flow into the matrix through ATP synthase to generate ATP in the matrix.

In the process of oxidative phosphorylation, electrons are eventually transferred to oxygen molecules from NADH and. The electron transfer chain is composed of a series of... 

Two and twelve moles of ATP are produced, respectively, per mole of glucose consumed in the glycolytic pathway and each turn of the Krebs (citrate) cycle. In fat metaboHsm, many high energy bonds are produced per mole of fatty ester oxidized. Eor example, 129 high energy phosphate bonds are produced per mole of palmitate. Oxidative phosphorylation has a remarkable 75% efficiency. Three moles of ATP are utilized per transfer of two electrons, compared to the theoretical four. The process occurs via a series of reactions involving flavoproteins, quinones such as coenzyme Q, and cytochromes. 

Dinitrophenol is a member of the aromatic family of pesticides, many of which exhibit insecticide and fungicide activity. DNP is considered to be highly toxic to humans, with a lethal oral dose of 14 to 43mg/kg. Environmental exposure to DNP occurs primarily from pesticide runoff to water. DNP is used as a pesticide, wood preservative, and in the manufacture of dyes. DNP is an uncoupler, or has the ability to separate the flow of electrons and the pumping of ions for ATP synthesis. This means that the energy from electron transfer cannot be used for ATP synthesis [75,77]. The mechanism of action of DNP is believed to inhibit the formation of ATP by uncoupling oxidative phosphorylation. 

Fig. 6.9 The catalysts for denitrification. Nitrate is reduced by a molybdenum enzyme while nitrite and oxides of nitrogen are reduced today mainly by copper enzymes. However, there are alternatives, probably earlier iron enzymes. The electron transfer bct complex is common to that in oxidative phosphorylation and similar to the bf complex of photosynthesis, while cytochrome c2 is to be compared with cytochrome c of oxidative phosphorylation. These four processes are linked in energy capture via proton (H+) gradients see Figure 6.8(a) and (b) and the lower parts of Fig. 6.9 which show separately the active site of the all iron NO-reductase, and the active site of cytochrome oxidase (02 reductase).

As fuel molecules are oxidized, the electrons they have lost are used to make NADH and FADH2. The function of the electron transport chain and oxidative phosphorylation is to take electrons from these molecules and transfer them to oxygen, making ATP in the process. 

The driving force of oxidative phosphorylation is the difference between the electron transfer potential of NADH or FADH2 relative to that of 02. For the redox couple... 

ASPECTS OF CARBOHYDRATE OXIDATION, ELECTRON TRANSFER, AND OXIDATIVE PHOSPHORYLATION... 

This was confirmed by Keilin and Hartree using antimycin A as an inhibitor. The antibiotic blocked the reduction of cytochrome cx by NADH or succinate but did not block the reduction of cytochrome b. This site-specific inhibition brought antimycin A into popular use by biochemists in the analysis of electron transfer and oxidative phosphorylation. 

The spatial separation between the components of the electron transport chain and the site of ATP synthesis was incompatible with simple interpretations of the chemical coupling hypothesis. In 1964, Paul Boyer suggested that conformational changes in components in the electron transport system consequent to electron transfer might be coupled to ATP formation, the conformational coupling hypothesis. No evidence for direct association has been forthcoming but conformational changes in the subunits of the FI particle are now included in the current mechanism for oxidative phosphorylation. 

Many enzymes in the mitochondria, including those of the citric acid cycle and pyruvate dehydrogenase, produce NADH, aU of which can be oxidized in the electron transport chain and in the process, capture energy for ATP synthesis by oxidative phosphorylation. If NADH is produced in the cytoplasm, either the malate shuttle or the a-glycerol phosphate shuttle can transfer the electrons into the mitochondria for delivery to the ETC. Once NADH has been oxidized, the NAD can again be used by enzymes that require it. 

Mitochondria, which are cytoplasmic organelles involved in cellular respiration, have their own chromosome, which contains 16,569 DNA base pairs (bp) arranged in a drcalar molecule. This DNA encodes 13 proteins that are subunits of complexes in the electron transport and oxidative phosphorylation processes (see Section 1, Chapter 13). In addition, mitochondrial DNA encodes 22 transfer RNAs and two ribosomal RNAs. 

The major role of electron transfer is the generation of ATP from ADP and P, (oxidative phosphorylation). Since the... 

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