A lot of websites aren't being specific and they are just saying that when electrons move from a high to low energy state during the ETC, "energy" is being released and that energy is used to pump (active transport) H+ ions through the membrane. I want to know more. Isn't ATP formed by adding a phosphate to ADP? If so, where do electrons moving through the ETC get that phosphate from? BTW, I'm not talking about ATP synthase, because you need H+ ions for ATP synthase and I'm not understanding how those H+ ions are being actively transported through the membrane in the first place.

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    $\begingroup$ On SE we expect you to do more research before posting, as you will find if you read the help on asking good questions. It's not sufficient to say "a lot of websites aren't being specific" — you need to find sources that treat the subject at a more advanced level. And the best sources are books, not websites. If you have the money, buy as many as you can afford. If not, try NCBI Bookshelf. For Biochemistry use Berg et al. — Try Chapter 18. $\endgroup$ – David Jan 23 '18 at 14:05
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    $\begingroup$ If you are referring to the active electron transport by complexes I-IV (which I guess you mean, by saying you're not referring to ATP synthase), then the most likely answer is 'we don't really know'. For ATP synthase the mechanism is quite well known, but for the ETC complexes I think I've only ever seen some structural/mechanical theory for one of the complexes. $\endgroup$ – Nicolai May 24 '18 at 16:38

ATP formation is done using the Complex V called as ATPsynthase (also called as F0/F1 particle) and the theory explaining this process is called as the Chemiosmotic Theory2.

During cellular respirationKreb’s cycle (in the mitochondria) and Light dependent Photophosphorylation photosynthesis (in the chloroplast thylakoids) a set of reactions establish a proton gradient across the inter-membrane space ( hereby referred to as IMS) of the mitochondria/chloroplast( if you remember mitochondria/chloroplast are double membrane bound organelles).

Just as in a battery/cell we have EMF(electron motive force) we have, in the IMS of the mitochondrion/chloroplasts, a proton motive force.

Since substances always flow from higher potential to lower potential, the IMS of mitochondrion/chloroplast having a high amount of protons is a region of high potential and lumen of mitochondrion/chloroplast is a region of low potential since there are less number of protons.

The only way protons can move from the IMS of the mitochondrion/chloroplast to the lumen of the mitochondrion/chloroplast is via the complex V (also known as ATPsynthase).

The ATPsynthase is a lollipop shaped protein structure that is freely rotatable and it brings ADP & phosphate molecules close together so that a covalent bond can be formed in between them.

How does it exactly do this you ask? So let’s summarise what all we have here:

  1. ATPsynthase that can rotate about its rotor.
  2. Proton gradient across the IMS ( high potential) and the lumen ( low potential).
  3. The only way out for the protons is via the ATPsynthase.

Now we can see a link here.

So what happens is, there’s the F0 subunit of the ATPsynthase through which the protons are able to move across the membrane and during that movement the rotate the F1 subunit. During this rotation shown in animation here the ADP & the phosphate group which are present in the active site of the F1 subunit are brought near each other and due to atomic interactions a bond is formed. The mechanical energy ( movement of protons across the membrane) is converted into chemical energy ( covalent bond) between the two molecules. This is the process via which the currency of the cell, ATP, is produced. Hope that answers the question.

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    $\begingroup$ I don't think you should answer questions in which the poster has not done his homework properly, but it you do, please read them first. What he writes is "I'm not talking about ATP synthase, because you need H+ ions for ATP synthase and I'm not understanding how those H+ ions are being actively transported through the membrane in the first place." You have described the ATP synthase — he wants to know how the proton gradient is established in the electron transport chain. I have told him where he can read about it for himself. $\endgroup$ – David Jan 23 '18 at 15:47
  • $\begingroup$ Oh, I see. Thank you for pointing it out. I thought he needed the mechanism of it. I think he needs to learn the cycles to completely understanding how H+ ions are being transported. I’ll be more careful next time. $\endgroup$ – Raheel Jan 23 '18 at 15:52

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