Biophysics: Concentration and Electric potential

1. Apr 20, 2014

fu11meta1

1. The problem statement, all variables and given/known data

Consider a membrane which is permeable to a singly charged ionic species. If the concentration on one side is 25 times that of the other, what is the electric potential required to maintain a net flux of zero at 37C?

2. Relevant equations

I'm not sure:
U = KQq/r
flux = Q/ε

3. The attempt at a solution

I was using K * Q * 25Q/R

But I'm getting no where

2. Apr 21, 2014

D.W.

I would check check this out:

http://en.wikipedia.org/wiki/Debye_length

There are a few equations there-in that might be useful to you.

I don't know how rigorous your Biophysics course is, but I remember doing problems like this having to do with modeling the net electric field and potential in the environment around charged DNA backbones and across membranes, and these equations, and the idea's they relate to, are what I used. If I have more time, I'll see if I can be more help than this.

EDIT: In particular, the section on "Debye length in an electrolyte" would be the most relevant to your interests.

Last edited: Apr 21, 2014
3. Apr 21, 2014

fu11meta1

Thank you, but I don't believe the problem is that in depth. Our course isn't very mathematically heavy , so it's usually basic formulas and whatnot. I just can't think of what to do -.-