questions regarding the electron transport chain in cellular respiration in humans?

Question

I have this from the textbook. "For every two NADH moleculaes, one O2 molecule is reduced to two molecules of water."
So does protons H+ play a role in forming water? or does the H+ protons(4 protons) just go through the respiratory chain from the mitochondrial matrix to the intermembrane space?

Answer 1

The protons play a role in forming water. As electrons go through the electron transport chain, H+ is pumped across the membrane, creating a gradient by having more H+ on the outside which will later cause H+ to physically flow inside through ATP synthase and form ATP. When the H+ that was pumped out through one of the complexes moves back into the matrix from the intermembrane space, it couples with electrons to make a complete hydrogen atom (one electron and one proton). Therefore, four electrons plus four protons (which combine again to make four hydrogens) plus one O2 combine to make 2 molecules of water.

The fact that NAD+ is reduced to NADH plus a proton is kind of confusing, but I believe it occurs because NAD+ will only bind to something that will give it no charge, and if it just accepted a hydrogen it would still be NADH+. I'm not completely sure about this, but this is how I interpreted my biochemistry teacher