Respiratory chain electron

ATP results from the movement of approximately three protons from the cytosol into the matrix through Fg. Altogether this means that approximately four protons are transported into the matrix per ATP synthesized. Thus, approximately one-fourth of the energy derived from the respiratory chain (electron transport and oxidative phosphorylation) is expended as the electrochemical energy devoted to mitochondrial ATP-ADP transport. 

Ubiquinone, known also as coenzyme Q, plays a crucial role as a respiratory chain electron carrier transport in inner mitochondrial membranes. It exerts this function through its reversible reduction to semiquinone or to fully hydrogenated ubiquinol, accepting two protons and two electrons. Because it is a small lipophilic molecule, it is freely diffusable within the inner mitochondrial membrane. Ubiquinones also act as important lipophilic endogenous antioxidants and have other functions of great importance for cellular metabolism. ... 

As in the respiratory chain (see p. 140), the light reactions cause electrons to pass from one redox system to the next in an electron transport chain. However, the direction of transport is opposite to that found in the respiratory chain. In the respiratory chain, electrons flow from NADH+H to O2, with the production of water and energy. 

Energy Span of the Respiratory Chain Electron transfer in the mitochondrial respiratory chain may be represented by the net reaction equation... 

In the overall reaction catalyzed by the mitochondrial respiratory chain, electrons move from NADH, succinate, or some other primary electron donor through flavoproteins, ubiquinone, iron-sulfur proteins, and cytochromes, and finally to 02. A look at the methods used to determine the sequence in which the carriers act is instructive, as the same general approaches have been used to study other electron-transfer chains, such as those of chloroplasts. 

FIGURE 19-15 Summary of the flow of electrons and protons through the four complexes of the respiratory chain. Electrons reach Q through Complexes I and II. QH2 serves as a mobile carrier of electrons and protons. It passes electrons to Complex III, which passes them to another mobile connecting link, cytochrome c. Complex IV... 

Figure 17.2. Respiratory chain. Electrons flow through Complex I (I)/Complex II (II), ubiquinone (Q), Complex III (III), cytochrome c (CytC), and Complex IV (IV) and protons are pumped from the matrix to the intermembrane space.

Figure 1 The mitochondrial respiratory chain. Electron transfer (brown arrows) between the three major membrane-bound complexes (I, III, and IV) is mediated by ubiquinone (Q/QH2) and the peripheral protein c)dochrome c (c). Transfer of protons hnked to the redox chemistry is shown by blue arrows red arrows denote proton translocation. NAD+ nicotinamide adenine dinucleotide, FMN flavin mononucleotide, Fe/S iron-sulfur center bH,bi, and c are the heme centers in the cytochrome bc complex (Complex III). Note the bifurcation of the electron transfer path on oxidation of QH2 by the heme bL - Fe/S center. Complex IV is the subject of this review. N and P denote the negatively and positively charged sides of the membrane, respectively...

The mitochondrial respiratory chain consists of several components that catalyze the reduction of molecular oxygen in vivo. In the respiratory chain, electrons are transported through a series of electron carriers as shown in Fig. 39. This concept has been deduced based on their standard reduction potentials. The order of the reduction potentials of the coenzymes investigated here i.e., CoQ>FMN and FAD>NAD is found to be consistent with the sequence of these coenzymes in the respiratory chain. In the reduction of these coenzymes, the parts being reduced at the electrode surface are the same as those in vivo. 

Iron-sulfur protein e. g. ferredoxin, complexes of the respiratory chain Electron transfer... 

In the respiratory chain, electrons from the powerful reducing agents NADH and FADH2 pass through four membrane-bound protein complexes and two mobile electron carriers before reducing O2 to H2O. We shall see that the electron transfer reactions drive the synthesis of ATP at three of the membrane protein complexes. 

Srinivas V, Leshchinsky I, Sang N, King MP, Minchenko A, Caro J. Oxygen sensing and HlF-1 activation does not require an active mitochondrial respiratory chain electron-transfer pathway. J Biol Chem 2001 276(25) 21995-21998. 

RESPIRATORY CHAIN (ELECTRON TRANS-PORT SYSTEM) ... 

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