The cell membrane is the locus of the respiratory electron transport system. In respiring bacteria, the flavoproteins, quinones, and cytochromes of the electron-transport chain are found in the inner surface of the bacterial membrane, as are the enzymes necessary for ATP synthesis. In certain electron microscope preparations, the inner surface of the membrane appears covered with tiny spheres on stalks.

These structures resemble the inner membrane spheres seen in mitochondria, and like them, they may be the locations at which respiration and ATP synthesis occur. Glycolysis takes place in the cytoplasm, or cell fluid, of the bacterium, as do the reactions of the citric acid cycle in those bacteria that respire. The reduced carrier molecules from glycolysis and the citric acid cycle then diffuse to the outer membrane and enter the respiratory chain.