This is one of the easiest exam questions to answer ever… its whatever your professor told you it was. This is how you will pass his/her exam. Alas, whether your professors desired response in a reality is truly correct or not is a whole other matter.
Historically, the answer was 36 or 38 depending upon which text book one used. Contemporary thinking puts it around the 30 figure.
The disparity in numbers is primarily driven by NADH and FADH2 multipliers which come about by the mechanisms / models utilized. It seems far from a trivial thing to exactly resolve one way or another.
The multiplier thing is intuitively hard to grasp. This video presents some of the background involved.
Its not mission critical to understanding the ratios, but one should be aware of protein complex numbering as to H+ production. I tend to believe this is correct, but a copy of it on Khanmedicine suggests otherwise…
Having spent hours on this rabbit trail, I tend to think the correction on Khanmedicine is correct… but I can also see why the videos author presented this the way she did.
A fellow student came up with the following from page 1103 of The Molecular Machinery of Keilin’s Respiratory Chain which seems to nail it. The entire article is pretty eye opening, but is more than a bit intense for those of us without a biochem background.
Electron transfer from succinate to oxygen will result in six H+ deposited outside (four due to bc1 complex and two due to cytochrome oxidase), six H+ taken up from the matrix (four due to bc1 complex and two due to cytochrome oxidase) and six charges translocated (two due to bc1 complex and fourdue to cytochrome oxidase). The majority view, although still perhaps open to possible question, is that electron transfer from NADH to ubiquinone through complex I is coupled tothe net translocation of four H+ and four charges across the membrane. The reduced ubiquinone is then reoxidized with the same outcome as succinate. Hence succinate oxidation is linked to six electrogenic proton translocations and NADH is linked to ten.