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I am looking into Glycolysis and TCA cycle. I have learnt that oxygen is the final electron acceptor.

So, let's say we know the amount of NADH and FADH2 produced under some circumstance related to the Glycolysis and TCA cycle.

How would we calculate the amount of oxygen consumption level?

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Assuming that you know the amount of NADH and FADH$_2$ produced by glycolysis and TCA cycle, you can determine the reducing equivalent produced: for each NADH or FADH$_2$ produced, two reducing equivalents are produced. It means that the re-oxidation of NADH and FADH$_2$ will release 2 electrons. Here are the corresponding half-reactions:

$\textrm{NADH} = \textrm{NAD}^+ + \textrm{H}^+ + 2~\textrm{e}^-$

$\textrm{FADH}_2 = \textrm{FAD} + 2~\textrm{H}^+ + 2~\textrm{e}^-$

Knowing the total reducing equivalent produced, divide it by four in order to obtain dioxygen consumption: O$_2$ is reduced into 2 H$_2$O by accepting four electrons. Here is the corresponding half-reaction:

$\textrm{O}_2 + 4~\textrm{e}^- + 4~\textrm{H}^+ = 2~\textrm{H}_2\textrm{O}$

Of course this only applies to aerobic organisms: some microbes are able to use other electron acceptors than O2.

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  • $\begingroup$ This is of course correct, though I think it might help to just write the reaction: 2 NADH + O2 -> 2 NAD+ + 2 H2O $\endgroup$ – Victor Chubukov Mar 3 '17 at 22:17
  • $\begingroup$ The half-reaction for oxygen reduction is not balanced, missing 4 H+. $\endgroup$ – Roland Mar 4 '17 at 16:53

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