Coupling of Electron Transport to ATP Production

According to the chemiosmotic theory, the electron-transport system, powered by the transport of electrons, pumps protons (H+) from the mitochondrial matrix into the space between the inner and outer mitochondrial membranes. The electron-transport system is grouped into three complexes that serve as proton pumps (fig. 5.10). The first pump (the NADH-coenzyme Q reductase complex) transports four H+ from the matrix to the intermembrane space for every pair of electrons moved along the electron-transport system. The second pump (the cy-tochrome c reductase complex) also transports four protons into the intermembrane space, and the third pump (the cytochrome c oxidase complex) transports two protons into the intermembrane space. As a result, there is a higher concentration of H+ in the intermembrane space than in the matrix, favoring the diffusion of H+ back out into the matrix. The inner mitochondrial membrane, however, does not permit diffusion of H+, except through structures called respiratory assemblies.

The respiratory assemblies consist of a group of proteins that form a "stem" and a globular subunit. The stem contains a channel through the inner mitochondrial membrane that permits the passage of protons (H+). The globular subunit, which protrudes into the matrix, contains an ATP synthase enzyme that is capable of catalyzing the reaction ADP + Pi ^ ATP when it is activated by the diffusion of protons through the respiratory assemblies and into the matrix (fig. 5.10). In this way, phosphory-lation (the addition of phosphate to ADP) is coupled to oxidation (the transport of electrons) in oxidative phosphorylation.

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Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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