Question

Complexes in eelectron transport chain of mitochondria

Answer 1

Electrons are transferred from NADH to O2 through a chain of three large protein complexes called NADH-Q oxidoreductase, Q-cytochrome c oxido-reductase, and cytochrome c oxidase . Electron flow within these transmembrane complexes leads to the transport of protons across the inner mitochondrial membrane. Electrons are carried from NADH-Q oxidoreductase to Q-cytochrome c oxidoreductase, the second complex of the chain, by the reduced form of coenzyme Q (Q), also known as ubiquinone because it is a ubiquitous quinone in biological systems. Ubiquinone is a hydrophobic quinone that diffuses rapidly within the inner mitochondrial membrane. Ubiquinone also carries electrons from FADH2, generated in succinate dehydrogenase in the citric acid cycle, to Q-cytochrome c oxidoreductase, generated through succinate-Q reductase. Cytochrome c, a small, soluble protein, shuttles electrons from Q-cytochrome c oxidoreductase to cytochrome c oxidase, the final component in the chain and the one that catalyzes the reduction of O2. NADH-Q oxidoreductase, succinate-Q reductase, Q-cytochrome c oxidoreductase, and cytochrome c oxidase are also called Complex I, II, III, and IV, respectively. Succinate-Q reductase (Complex II), in contrast with the other complexes, does not pump protons.


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