Principles of Biochemistry Volume 2 - A. Lehninger 1985

Bioenergetics and Metabolism
Electron Transport, Oxidative Phosphorylation, and Regulation of ATP Synthesis
Electron transport and oxidative phosphorylation take place in the inner mitochondrial membrane.

In Eukaryotic Cells, almost all of the specific dehydrogenases involved in the Oxidation of Pyruvate and other cellular fuels via The Citric Acid Cycle reside within the inner compartment of Cell/35.html">Mitochondria—their matrix (Fig. 17-2). The inner mitochondrial membrane houses the electron carriers that comprise the Respiratory Chain, as well as the Enzymes that catalyze ATP synthesis from ADP and phosphate. Fuel molecules for The Citric Acid cycle, such as pyruvate, must move from the Cytosol—where they are produced—into the mitochondrial matrix to be acted upon by dehydrogenases, which naturally requires them to cross both mitochondrial membranes. Similarly, ADP generated from ATP in the cytosol during various energy-requiring processes must enter the mitochondrial matrix to be rephosphorylated to ATP. The newly formed ATP must then return to the cytosol. The inner mitochondrial membrane contains specialized transport systems (Section 17.19) that shuttle pyruvate and other cellular fuels from the cytosol into the mitochondria, while also mediating the influx of ADP and phosphate and the efflux of ATP during Oxidative Phosphorylation. Thus, the inner mitochondrial membrane is composed of numerous components. It incorporates electron carriers, a series of enzymes, and several membrane transport systems. Together, these components account for up to 75% or even more of the total membrane mass, with Lipids making up the remainder. The inner mitochondrial membrane features a complex mosaic Structure whose integrity is essential for such a vital function as ATP synthesis.

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Fig. 17-2. Biochemical anatomy of a mitochondrion. The localization of citric acid cycle enzymes, Electron Transport Chains, oxidative phosphorylation enzymes, and the internal coenzyme pool is indicated. The inner membrane of a single rat Liver mitochondrion may contain over 10,000 sets of electron transport chains and ATP synthase molecules. The number of such sets increases with the surface area of the inner membrane. Heart mitochondria, with their abundant cristae, contain three times as many such sets as liver mitochondria. The internal pool of Coenzymes and intermediates is functionally segregated from the corresponding cytoplasmic pool. The mitochondrial structure is described in detail in Chapter 2.