enter image description hereAccording to an answer in this question, my concept used below does not apply:

In the non-cyclic photophosphorylation, consider splitting of two water molecules, then 4 e- (electrons) and 4 H+ (protons) are generated in the lumen of the thylakoid. Due to quinone cycle 8 H+ are transferred from stroma to lumen. 4 e- will reduce 2 NADP+ to 2 NADPH, these H+ are taken from stroma so there is a net decrease of 8 + 2 = 10 H+ and a net increase of 4 + 8 = 12 H+ in the lumen. So if we apply principles of chemistry then to attain equilibrium there should be equal number of H+ on both side. Therefore 11 H+ must be transferred from lumen of thylakoid to stroma. Now there is 1 H+ on each side at equilibrium. We know that F0-F1 ATPase will produce 1 ATP for 3 H+ being transferred so in this process 11/3 ATP should produce but in books it is given that all 12 H+ are transported which is violating the principle of chemical equilibrium and produces 12/3=4 ATP.

So I basically want to ask: Why does it seem that in this process the principles of chemistry are violated?

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    $\begingroup$ About which principles of chemistry are you talking? $\endgroup$
    – Chris
    Feb 12 '16 at 14:02
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    $\begingroup$ @chris According to books all 12p will get transferred but we know from chemistry point of view that only 11p could get transferred as per the gradient created $\endgroup$
    – JM97
    Feb 12 '16 at 14:06
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    $\begingroup$ @Chris the principle is that at equilibrium there must equal number of protons on both sides $\endgroup$
    – JM97
    Feb 12 '16 at 14:13
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    $\begingroup$ A schematic of the reactions involved would help. It's kind of a narrative. $\endgroup$
    – AliceD
    Feb 13 '16 at 19:54
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    $\begingroup$ You should just write down the equation. Here is an explanation on how to write chemistry expression. Then, you'll probably want to use the term stoichiometry somewhere in your post. Finally, note that your question would be a better fit for Chemistry.SE than for Biology.SE but I would predict that the level of knowledge in chemistry needed to answer the question will be simple enough for us, biologists. $\endgroup$
    – Remi.b
    Feb 14 '16 at 1:07

From the link given by @Kendall

Such a gradient can be maintained because the thylakoid membrane is essentially impermeable to protons.

I think this solves your dilemma of 'why not maintaining equilibrium' totally.

The reason for this difference is that the thylakoid membrane is quite permeable to Cl- and Mg2+. The light-induced transfer of H+ into the thylakoid space is accompanied by the transfer of either Cl- in the same direction or Mg2+ (1 Mg2+ per 2 H+) in the opposite direction. Consequently, electrical neutrality is maintained and no membrane potential is generated.

It precisely shows why electrical equilibrium is not disturbed due to pH disturbance.


2 H2O + 2 NADP+ + 10 H+stroma => O2 + 2NADPH + 12 H+lumen

12 H+lumen + 4 ADP + 4 Pi => 4 ATP + 12 H+stroma


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