BIOG 1105-1106 | Cornell Introductory Biology, Individualized Instruction

The stoichiometry of oxidative phosphorylation was worked out here at Cornell in Professor Peter Hinkle's Lab. You are not responsible for the details provided below, but the following diagram may help your understanding of this crucial process.

Notice that at site 1 (Complex I in our diagram), 4 H+ ions are transported across the membrane for each pair of electrons that are accepted from NADH + H+.
At site 2 (Complex III in our diagram), 2 H+ ions are transported across the membrane for each pair of electrons.
At site 3 (Complex IV) 4 H+ ions are transported across the membrane for each pair of electrons.
The total number of H+ ions transported across the membrane is 10.
It takes a total of 4 H+ ions for the synthesis of one ATP: three are used directly by ATP synthase, and one is used in the uptake of ADP and Pi by the adenine nucleotide transporter (AT) and phosphate transporter. (PT)
It follows then, that if 10 H+ ions are effectively transported across the membrane, a net gain of 10/4 or 2.5 ATP can be produced. Since the electrons from FADH₂ and the NADHs produced in glycolysis enter the chain at Q, only 6 H+ ions are transported across, so only 1.5 ATP can be produced.