The following images attempt to illustrate
how the electron transport chain (ETC) creates a proton gradient
that powers the synthesis of ATP. These images are intended to emphasize
the key steps in these processes. Clicking on each of the
thumbnail images will bring up a larger, labeled version of the
see the Flash movie for the following sequence of images,
The electron transport
chain (ETC) is located in the inner
membrane of the mitochondria.
NADH is the electron
donor for the ETC.
Electron donation to the first complex
(blue) and hydrogen ion pumping are coupled.
The donated electrons are then passed
to the first mobile carrier protein (pink).
The electrons are then passed to the second
complex (red). This transfer is again coupled with the pumping
of hydrogen ions.
Electrons are then passed to the second
mobile carrier protein (purple).
Next, the electrons are transferred to
the third complex (orange).
While contained by the third complex,
the electrons interact with oxygen and hydrogen
The reaction ends with hydrogen ions,
or protons, being pumped across the membrane
and the release of water molecules (H2O).
The pumping of protons creates a proton
The hydrogen ion pumping actions of the
ETC are coupled with ATP synthesis.