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Cytochromes are proteins with prosthetic groups called heme groups (4 organic rings around one iron atom; similar to hemoglobin but transfers electrons not oxygen).  Prosthetic Groups are non-protein components essential for catalytic functions of certain enzymes.  They alternate between oxidized and reduced as they donate and accept electrons.

ETC pumps protons to run ATP Synthase

The ETC is located on the inner mitochondrial membrane.  The ETCs job is to release energy in smaller quantities/steps to make the energy more manageable.  Some members of the ETC must accept/release protons along with electrons.  At certain steps along the ETC, H⁺ is accepted and expelled into the intermembrane space.  Electron carriers are spatially arranged such that the aforementioned occurs.  The H⁺ gradient that results is called Proton-Motive Force.

Oxidative phosphorylation is the means of ATP production in this process.

FADH₂ gives 1/3 less energy than NADH because it adds electrons to the ETC at a lower energy level.

ATP Synthase makes ATP

The enzyme works like an ion pump in reverse.  It uses energy in an existing gradient (proton gradient) to make ATP.  The proton gradient is the difference in pH on opposite sides of the membrane that indirectly makes ATP.  Click here to see how ATP Synthase uses the gradient (link as of June 1999).

Next:  "Fermentation."