membrane permeability

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membrane permeability

Post by NewtoBiology » Wed Jul 15, 2009 11:40 pm

Hello Biologists,

Q: Assume that the plasma membrane of a cell was suddenly permeable to the same degree to both Na+ and K+ and that teach responded to a concentration gradient of the same magnitude. Would you expect those two ions to move across the membrane at the same rates? Why or why not?

I always take a galliant effort to try to answer my own questions before posting. I have researched this possibility and come up with a solution. I am wondering you biologists would be so kind to read it and offer any additional thoughts.

A: I know that inorder for Na+ and K+ ions to move in and out of a cell they need an NA+/K+ ATase, therefore if a membrane was suddenly permeable to the same degree to both Na+ and K+ the two ions could not move across the membane at the same rate! In the second step of Na+/K+ ATPase 3 Na+ ions move out of the cell into the extracellular space reducing an ATP molecule to ADP. In turn, in the 4th step of the NA+/K+ ATPase, two K+ ions move into the cell, while also loosing an attached phosphate molecule. Therefore regardless of the sudden permeabilty change, the ration of Na+/K+ is still 3:2.

Thank you for your time


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Post by kolean » Wed Jul 22, 2009 2:33 am

If the plasma membrane was permeable to the same degree to both Na+ and K+, then they would not have to use the ATPase. And since the concentration gradient of both ions are of the same magnitude, then I would expect the ions to move across the membrane at pretty much the same rate (even though K is a bigger atom than Na). The only thing different is that Na+ would be going in, while K+ would be going out, till the concentration of each ion was the same inside the cell to outside the cell establishing equilibrium.

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Re: membrane permeability

Post by ankitakhemka » Wed Jul 22, 2009 12:11 pm

hi , if both ions will move with the same conc and same time then the required conc may not balanced and also as you say both requires different conditions that is ADP and ATP thus they may not pass at the same time.

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