Copyright 1997. Thomas M. Terry, The University of Connecticut.

Animation of Chemiosmotic ATP synthesis in Bacteria

Step 1: Proton gradient is built up as a result of NADH (produced from oxidation reactions) feeding electrons into the electron transport system. As these electrons are transported through a series of electron carriers, protons are translocated to the outside face of the cell membrane.

Step 2: Protons (indicated by + charge) enter back into the bacterial cytoplasm through channels in ATP synthase enzyme complex. This entry is coupled to ATP synthesis from ADP and phosphate (P_i)

Go to Animation of electron transport in Bacteria

The schematic diagram above illustrates a bacterial cell. In the animation, watch as H⁺ ions accumulate just outside the cell membrane whenever NADH is made from oxidation reactions, generating a proton gradient (upper image). Protons re-enter the cell through the ATP synthase complex, generating ATP (lower image).
Key points:

Protons are first translocated across the membrane, from the cytoplasm to the periplasmic space, as a result of electron transport resulting from the formation of NADH by oxidation reactions. (See animation of electron transport if you don't understand this step.) The continued buildup of these protons creates a proton gradient.
ATP synthase is a large protein complex with a proton channel that allows re-entry of protons.
ATP synthesis is driven by the resulting current of protons flowing through the membrane:
ADP + P_i---> ATP

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