Electron transport release from phosphorylation

The two processes are electron transport and oxidative phosphorylation. NADH is reoxidised by the process of electron transport using the electron transport chain and the energy released from this process is harnessed by oxidative phosphorylation to generate ATP. We noted earlier that the two processes are intimately linked or coupled. Normally one cannot proceed without the other. 

In eukaryotes, electron transport and oxidative phosphorylation occur in the inner membrane of mitochondria. These processes re-oxidize the NADH and FADH2 that arise from the citric acid cycle (located in the mitochondrial matrix Topic L2), glycolysis (located in the cytoplasm Topic J3) and fatty acid oxidation (located in the mitochondrial matrix Topic K2) and trap the energy released as ATP. Oxidative phosphorylation is by far the major source of ATP in the cell. In prokaryotes, the components of electron transport and oxidative phosphorylation are located in the plasma membrane (see Topic Al). 

The citric acid cycle is a sequence of reactions in which the two carbon atoms of acetyl-CoA are ultimately oxidized to C02. It is the central pathway for the release of energy from acetyl-CoA, which is produced from the catabolism of carbohydrates (Chap. 11), fatty acids (Chap. 13), and some amino acids (Chap. 15) and is closely involved with two other processes, namely, electron transport and oxidative phosphorylation (Chap. 14). 

Submitochondrial particles (SMPs) are produced by disruption of the mitochondria by mechanical, osmotic, or sonic shock treatment. The fragmentation results in the release of water-soluble components and inner membrane fragments that re-form into vesicles (Figure 14-2). The components are then separated by differential centrifugation. The membranes of SMPs have the characteristic inner membrane spheres on their outside. SMPs are capable of electron transport and oxidative phosphorylation (i.e., the synthesis of ATP from ADP and phosphate). Removal of the inner membrane spheres by further mechanical treatment, urea, or trypsin results in the dissociation of the electron transport assembly from ATP synthesis. The ability to synthesize ATP resides in the overall structure, which includes the spheres (called FO, the stalks, and a membrane protein subunit (called Fq). The Fo-subunit spans the inner membrane and thus is retained in the vesicles. 

The final stage in the extraction of energy from food is oxidative phosphorylation, in which the energy of NADH and FADHj is released via the electron transport chain (ETC) and used by an ATP synthase to produce ATP. This process requires O. ... 

Photosynthesis occurs in the plant cell organelle called the chloroplast. During the process of photosynthesis, electrons are transferred from H20 to NADP+ via an electron carrier system. The energy released by electron transport is converted into the form of a proton gradient and coupled to ADP phosphorylation. In this experiment a method is introduced to demonstrate the formation of the proton gradient across the chloroplast membranes. 

Some evidence for a much closer functional relationship between the electron transport and proton translocation on one hand and the phosphorylation on the other hand in chloroplasts is given by a recent report from Prochaska and Dilley.17 This report shows that in chloroplasts the protons released from water in the photoreaction of photosystem II are sequestered in the membrane and interact directly with a particular subunit of the CF within the membrane. Recent evidence from other laboratories, including our own,18 9 all points to a much more localized mech-... 

Uncouplers Release Electron Transport from Phosphorylation... 

The focus of this article will be upon those aspects of the structure and function of cytochrome c oxidase that contribute particularly to an understanding of the chemical events that lead to the reduction of dioxygen to water. This important function is, however, only one aspect of its physiological role. The functioning enzyme is provided with electrons from the electron transport chain by cytochrome c, uses these electrons to reduce dioxygen bound at the active site, communicates the energy released in this reduction to the site of oxidative phosphorylation,... 

ATP is produced from ADP (adenosine diphosphate) by coupling the release of electrons to the reaction of organic phosphates and ADP producing ATP. ATP has two modes of production substrate-level phosphorylation and oxidative phosphorylation. In the former, the electrons released by the energy source are absorbed by an intermediate product within the system. The electron absorption is accompanied by an energy release and ATP is formed. The electron-transport system is simple. 

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