- A Neutral Protein Carrier May Help An Ion To Transfer Into And Cross A Lipid Membrane A How Would You Approach Model 1 (712.83 KiB) Viewed 14 times
A neutral protein “carrier” may help an ion to transfer into and cross a lipid membrane. a) How would you approach modelling this ion with electrostatics? In other words, what kind of shape would you use to model this ion? What charge q would this shape have? b) Let's model water and the lipid membrane as two solutions with a dielectric constant, D. Water has a dielectric constant of 80, and the lipid membrane (our “hydrocarbon solvent”) has a dielectric constant of 2. Write down an equation for the ion's energy in each medium using the given model q2 U = 41Deo(2R) c) What is the Bjerrum length lp? Simplify your two equations in (b) using the mathematical expression for the Bjerrum length. d) Calculate the electrostatic free energy change when a monovalent ion is transferred from water at 25°C (13=708) to a hydrocarbon solvent (lb =2808). Assume R is approximately 28 (+1 bonus: what is R?). By what factor does the energy of the ion change when it enters the lipid membrane? e) Comment on the ability of the ions to diffuse through the lipid bilayers. How has nature solved this problem? How do ions manage to get across?