PROBLEM Oxidative Phosphorylation

[plasmaprestige]

Let me preface this by saying I am a senior in high school taking AP Biology. Currently, we are studying glycolysis, TCA cycle, and oxidative phosphorylation.

 

Were taught many years ago that the oxidation of glucose to harvest energy can be generalized by

 

C6H12O6 + 6O2 -> 6CO2 + 6H2O

 

I am trying to account for where all of these molecules are either consumed or made.

 

One glucose is used in glycolysis, which makes 2 NADH + 2 protons. Pyruvate oxidation creates an additional 2 NADH + 2 protons and 2 CO2 (per glucose). Two cycles of the TCA cycle produce 6 NADH + 6 protons, 2 FADH2, and 4 CO2. So far, the glucose and the CO2 have been entirely accounted for. I excluded water because two waters are made from glycolysis but 2 are used again in TCA cycle.

 

So, 10 NADH + 10 protons and 2 FADH2 enter the electron transport chain. They donate, collectively, 12 pairs of electrons, which ultimately result in the reduction of 3 molecules of oxygen (O2) to make 6 H2O. O2 doesn't fit. I say 3 molecules and not 6 because each oxygen molecule needs 4 electrons (and protons) before it can become 2 H2O.

 

This does not match with the generalized equation. I have consulted a few biochemistry texts, but was unsuccessful in finding a satisfactory explanation. Can someone please explain this?

Edited January 10, 2013 by plasmaprestige

[BabcockHall]

Twelve pairs of electrons is twenty four electrons. That is enough to reduce six molecules of O₂.

[vampares]

err? There are 12 electrons from my count. Not pairs.

 

These electrons go to ATP ?

[BabcockHall]

No, Each NADH has a pair of electrons to give (ultimately) to oxygen. The same is true of FADH₂. To verify this you can assign oxidation numbers to the relevant carbon atoms in the molecules. The electrons go through the electron transport chain to oxygen. When they do, a protonmotive force (pmf) is built up, and this is the energy used for the synthesis of ATP. In other words, the electrons do not go to ATP. The protonmotive force is a type of electrochemical gradient. Peter Mitchell first proposed this was the driving force for synthesis of ATP, to the best of my knowledge.

Edited February 5, 2013 by BabcockHall