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H+ concentration gradient Photosynthesis

  1. Mar 16, 2005 #1
    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?


  2. jcsd
  3. Mar 16, 2005 #2


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    Does this statement help:

    The cytochrome b6/f complex acts to pump H+ across the thylakoid during electron transport
  4. Mar 16, 2005 #3
    so this is exactly the same as cyclic phosphorylation then? energy from e- is used to pump H+ across thylakoid membrane?
  5. Mar 16, 2005 #4
    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?
  6. Mar 16, 2005 #5


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    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 [Broken]
    Last edited by a moderator: May 1, 2017
  7. Mar 17, 2005 #6
    why go through H+? why can't the energy from the electrons be directly used to synthesise ATP?
  8. Mar 24, 2005 #7
    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.
  9. Mar 25, 2005 #8
    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.

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