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    So the book says: Hydrogen ions are actively pumped out of the companion cell into the surrounding tissues using ATP. The hydrogen ions return to the companion cell down a concentration gradient via a co-transport protein.
    what i dont understand is why does the H+ ion move into the surrounding tissue at the first place? Is it to aid the co-transportation of sucrose?
    thanks a lot!
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    (Original post by tifflcy)
    So the book says: Hydrogen ions are actively pumped out of the companion cell into the surrounding tissues using ATP. The hydrogen ions return to the companion cell down a concentration gradient via a co-transport protein.
    what i dont understand is why does the H+ ion move into the surrounding tissue at the first place? Is it to aid the co-transportation of sucrose?
    thanks a lot!
    You're right.

    When sucrose moves into the sink cells, it moves via a co-transport protein called a H+/Sucrose symporter. It's exactly like the sodium-glucose co-transporter you find in the epithelial cells.

    When the hydrogen ions, aka protons, move back into the companion cell, it binds sucrose molecules as well and thus sucrose moves against it's concentration gradient, allowing maximum absorption of sucrose and other photosynthates.

    If you were to use a channel protein that allows sucrose to move via facilitated diffusion, then an equilibrium would establish and we don't want an equilibrium.
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    (Original post by RMNDK)
    You're right.

    When sucrose moves into the sink cells, it moves via a co-transport protein called a H+/Sucrose symporter. It's exactly like the sodium-glucose co-transporter you find in the epithelial cells.

    When the hydrogen ions, aka protons, move back into the companion cell, it binds sucrose molecules as well and thus sucrose moves against it's concentration gradient, allowing maximum absorption of sucrose and other photosynthates.

    If you were to use a channel protein that allows sucrose to move via facilitated diffusion, then an equilibrium would establish and we don't want an equilibrium.
    Thank you so much! (Esp replying on a sunday hahaa)
 
 
 
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