Although bacteria lack any internal membranes, aerobic bacteria nonetheless carry out oxidative phosphorylation by the same processes that occur in eukaryotic mitochondria. Enzymes that catalyze the reactions of both the glycolytic pathway and the citric acid cycle are present in the cytosol of bacteria; enzymes that oxidize NADH to NAD+ and transfer the electrons to the ultimate acceptor O2 are localized to the bacterial plasma membrane.
The movement of electrons through these membrane carriers is coupled to the pumping of protons out of the cell (see Figure 8-2). The movement of protons back into the cell, down their concentration gradient, is coupled to the synthesis of ATP. Bacterial F0F1 complexes are essentially identical in structure and function with the mitochondrial F0F1 complex, but are simpler to purify and study. The protonmotive force across the bacterial plasma membrane is also used to power the uptake of nutrients such as sugars, using proton/sugar symporters, and the rotation of bacterial flagella (see Figure 8-1). As we noted earlier, a primitive aerobic bacterium was probably the progenitor of mitochondria in eukaryotic cells (see Figure 8-3).
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