H+ concentration gradient Photosynthesis

AI Thread Summary
The discussion focuses on the mechanisms maintaining the H+ concentration gradient across the thylakoid membrane during the light-dependent reactions of photosynthesis. Key points include the role of the cytochrome b6/f complex, which pumps H+ ions into the thylakoid lumen during electron transport from photosystem II. This process is essential for creating the electrochemical gradient necessary for ATP synthesis via ATP synthase. The participants clarify that energy from electrons cannot be directly used to synthesize ATP; instead, it must first be converted into a proton gradient, which is then utilized by ATP synthase to produce ATP. The structure of ATP synthase requires this H+ gradient, explaining why the process is indirect and involves multiple steps. The discussion concludes with an acknowledgment of the complexity and necessity of this mechanism in photosynthesis.
garytse86
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FOr the light dependent reaction, In the textbook it says that the H+ concentration gradient across the thylakoid membrane is maintained by:

1) photolysis
2) transport of electrons from photosystem II along carriers
3) formation of NADPH.

I can understand 1) and 3), but I have no idea how transport of e- would maintain a hydrogen ion concentration gradient. Can someone help please?

THanks.

Gary
 
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Does this statement help:

The cytochrome b6/f complex acts to pump H+ across the thylakoid during electron transport
 
so this is exactly the same as cyclic phosphorylation then? energy from e- is used to pump H+ across thylakoid membrane?
 
but it seems silly for plants to have evolved such mechanisms.
Why pump the hydrogen into the lumen, and when they diffuse out along the electrochemical gradient the energy is used to synthesise ATP. Why go through this process, why can't the energy just be used to synthesise ATP in the first place?
 
Energy for e- is used to pump H+ out. ATP is synthesis due to that process, which is why H+ are pump out.

Look at the figure
http://bio.winona.msus.edu/bates/Bio241/images/figure-08-12-1.jpg
 
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why go through H+? why can't the energy from the electrons be directly used to synthesise ATP?
 
There is no mechanism to do it directly. ATP synthase is powered by the proton gradient. The only way to make ATP is to use the enzyme ATP synthase, because of the structure of the ATP. Energy has to be transferred from photons to electrons to the H+ gradient, then to ATP.
 
nipwoni said:
There is no mechanism to do it directly. ATP synthase is powered by the proton gradient. The only way to make ATP is to use the enzyme ATP synthase, because of the structure of the ATP. Energy has to be transferred from photons to electrons to the H+ gradient, then to ATP.
oh now i get it. It is because of the structure of the enzyme which needs a H+ gradient.


Many thanks to all of you.

Gary
 

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