Mitochondria Electron transport system

In eukaryotes, most of the reactions of aerobic energy metabolism occur in mitochondria. An inner membrane separates the mitochondrion into two spaces the internal matrix space and the intermembrane space. An electron-transport system in the inner membrane oxidizes NADH and succinate at the expense of 02, generating ATP in the process. The operation of the respiratory chain and its coupling to ATP synthesis can be summarized as follows ... 

The next step in building a biochemical network model for the TCA cycle is determining the governing differential equations. Since we are not treating transport of material into or out of the mitochondrion, the reactants of the overall reaction of Equation (6.31) are held clamped in this model. In addition, ASP and GLU are held fixed because there are no sources or sinks for the metabolites other than the aspartate aminotransferase reaction built into the model at this stage. Since the electron transport system is not modeled, proton transport is not included and pH is held fixed. 

As mentioned, the battery cell process is analogous to the living cell process of the mitochondrion, the chloroplast, and the electron-transport system in the cytoplasmic membrane of the procaryotes. Thus, Equation (15.11) can represent the basic thermodynamics of a microbial system. 

Krebs cycle Citric acid cycle, TCA cycle, the mitochondrial process by which acetyl groups from acetyl-CoA are oxidized to CO. The reducing equivalents are captured as NADH and FADH, which feed into the electron transport system of the mitochondrion to produce ATP via oxidative phosphorylation. 

The electron transport chain (ETC) or electron transport system (ETS) shown in Figure 16-1 is located on the inner membrane of the mitochondrion and is responsible for the harnessing of free energy released as electrons travel from more reduced (more negative reduction potential, E to more oxidized (more positive carriers to drive the phosphorylation of ADP to ATP. Complex 1 accepts a pair of electrons from NADH ( = -0.32 V)... 

How does brown fat generate heat and burn excess calories For the answer we must turn to the mitochondrion. In addition to the ATP synthase and the electron transport system proteins that are found in all mitochondria, there is a protein in the inner mitochondrial membrane of brown fat tissue called thermogenin. This protein has a channel in the center through which the protons (H ) of the intermembrane space could pass back into the mitochondrial matrix. Under normal conditions this channel is plugged by a GDP molecule so that it remains closed and the proton gradient can continue to drive ATP synthesis by oxidative phosphorylation. 

NADH carries electrons to the electron transport system inside the mitochondrion via a shuttle system (Figure 15.11). Electrons that enter via the shuttle in Figure 15.11a bypass complex I of the electron transport system, whereas electrons that enter via the shuttle in Figure 15,11b enter at complex L... 

These enzymes contain FAD, and the reduced coenzyme FADH2 that is formed is reoxidized by an electron transferring flavoprotein (Chapter 15), which also contains FAD. This protein carries the electrons abstracted in the oxidation process to the inner membrane of the mitochondrion where they enter the mitochondrial electron transport system, as depicted in Fig. 10-5 and as discussed in detail in... 

Fig. 4.22 The biochemical anatomy of mitochondria, showing the location enzymes of the citric acid cycle, the electron-transport chains, the en catalysing oxidative phosphorylation, and the internal pool of coenzymes. The muai membrane of a single liver mitochondrion may have over 10 000 sets of electron-transpKjrt chains and ATP synthetase molecules. The number of sets is proportional to the area of the inner membrane. Heart mitochondria, which have very profuse cristae and thus a much larger area of inner membrane, contain over three times as many sets of electron-transport systems as liver mitochondria. The internal pool of coenzymes and intermediates is functionally separate from the cytosolic pool.

Two organelles, the mitochondrion and the chloroplast, have extensive internal membranes which support electron-transport systems necessary for the production of energy. Mitochondria are found in most eukaryotic cells whereas chloroplasts are restricted to plant cells. 

The processes of electron transport and oxidative phosphorylation are membrane-associated. Bacteria are the simplest life form, and bacterial cells typically consist of a single cellular compartment surrounded by a plasma membrane and a more rigid cell wall. In such a system, the conversion of energy from NADH and [FADHg] to the energy of ATP via electron transport and oxidative phosphorylation is carried out at (and across) the plasma membrane. In eukaryotic cells, electron transport and oxidative phosphorylation are localized in mitochondria, which are also the sites of TCA cycle activity and (as we shall see in Chapter 24) fatty acid oxidation. Mammalian cells contain from 800 to 2500 mitochondria other types of cells may have as few as one or two or as many as half a million mitochondria. Human erythrocytes, whose purpose is simply to transport oxygen to tissues, contain no mitochondria at all. The typical mitochondrion is about 0.5 0.3 microns in diameter and from 0.5 micron to several microns long its overall shape is sensitive to metabolic conditions in the cell. 

It has been known for many years that the mitochondrion shows a respiration-linked transport of a number of ions. Of these, calcium has attracted the most attention since it depends on a specific transport system with high-affinity binding sites. The uptake of calcium usually also involves a permeant anion, but in the absence of this, protons are ejected as the electron transfer system operates. The result is either the accumulation of calcium salts in the mitochondrial matrix or an alkalinization of the interior of the mitochondrion. The transfer of calcium inwards stimulates oxygen utilization but provides an alternative to the oxidative phosphorylation of ADP618 ... 

Mitochondrion—The site for the electron-transport and the respiratory enzyme systems in eucaryotes. 

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