Free energy electron transport

As we have seen, the metabolic energy from oxidation of food materials—sugars, fats, and amino acids—is funneled into formation of reduced coenzymes (NADH) and reduced flavoproteins ([FADHg]). The electron transport chain reoxidizes the coenzymes, and channels the free energy obtained from these reactions into the synthesis of ATP. This reoxidation process involves the removal of both protons and electrons from the coenzymes. Electrons move from NADH and [FADHg] to molecular oxygen, Og, which is the terminal acceptor of electrons in the chain. The reoxidation of NADH,... 

The energetics of the electron transport steps makes the process work. Overall there s a lot of free energy lost in the tranfer of electrons from NADH to oxygen—the overall reaction is very favorable, with an equilibrium constant that s overwhelmingly large. At the three sites where ATPs are made (labeled I, II, and III), the reaction is the most downhill. 

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