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We now move our discussion past complexes I-IV on to complex V, called oxidative phosphorylation, in which ATP is synthesized from ADP and phosphate in the matrix of mitochondria. The enzyme that catalyzes this reaction is called ATP synthase the protein component of complex V.
As we introduced in the last section, as a result of the electron transport chain, an electrochemical gradient is formed on either side of the inner mitochondrial membrane. The outside of the membrane is positive while the inside is negative. The positive hydrogen ions are allowed to flow back across the membrane through specialized channels manned by ATP synthase, which uses the energy created by the energetically favorable transport to synthesize ADP and phosphate into ATP. This process is also called chemiosmosis.
Figure 3.10: Oxidative Phosphorylation
The transport of just two electrons through the electron transport chain generates enough free energy in the form of an electrochemical gradient to drive the synthesis of one molecule of ATP. The synthesis of ATP necessitates the dissolution of the electrochemical gradient, however, since the whole process is driven by positive hydrogen ions (protons) flowing back into the matrix space from the intermembrane space. The ETC maintains the electrochemical gradient by continuing to generate hydrogen ions.
In total, the process started through the glycolysis of one glucose molecule yields up to 34 ATP in oxidative phosphorylation. In total, oxidative phosphorylation accounts for around 90 percent of the body's total ATP.
In addition to ATP generation, oxidative phosphorylation produces heat. Endothermic organisms, like mammals, can use this heat to regulate body temperature.
Conclusion
We have now concluded our study of cell respiration, following the entire process of a glucose molecule from the cytosol and glycolysis into mitochondria and through the electron transport chain and oxidative phosphorylation. It is worth noting that other biological macromolecules also yield ATP and can also be broken down through cellular respiration. For instance, peroxisomes break down lipids to produce energy. With our new knowledge, we can now produce an updated version of our overall map of cell metabolism and how the ATP that powers cellular work is produced.
Figure 3.11: Map of Cell Metabolism
