Question

Describe the relationship between the redox potentials and electrical respiratory chain.

Answer 1

The redox potential (designated E′₀) increases as electrons flow down the respiratory chain to oxygen. Electrons flow through a respiratory enzyme complex by passing in sequence through the multiple electron carriers in each complex. As indicated, part of the favorable free-energy change is harnessed by each enzyme complex to pump H⁺ across the inner mitochondrial membrane. It is thought that the NADH dehydrogenase and cytochrome b-c₁ complexes each pump two H⁺ per electron, whereas the cytochrome oxidase complex pumps one. It should be noted that NADH is not the only source of electrons for the respiratory chain. The flavin FADH₂ is also generated by fatty acid oxidation and by the citric acid cycle. Its two electrons are passed directly to ubiquinone, bypassing NADH dehydrogenase; they therefore cause less H⁺ pumping than the two electrons transported from NADH.