The complete oxidation of glucose during the first three stages of cellular respiration results in the production of two kinds of reduced electron carriers: NADH and FADH2. We are now going to see how the energy stored in these electron carriers is used to synthesize ATP.
The energy in these electron carriers is released in a series of redox reactions that occur as electrons pass through a chain of protein complexes in the inner mitochondrial membrane to the final electron acceptor, oxygen, which is reduced to water. The energy released by these redox reactions is not converted directly into the chemical energy of ATP, however. Instead, the passage of electrons is coupled to the transfer of protons (H+) across the inner mitochondrial membrane, creating a concentration and charge gradient (Chapter 5). This electrochemical gradient provides a source of potential energy that is then used to drive the synthesis of ATP.
We next explore the properties of the electron transport chain, the proton gradient, and the synthesis of ATP.