Movie 2. Probability [Low affinity] = 1. This movie illustrates a Monte Carlo simulation by using a selectivity filter with one K-binding site that is fixed in the low-affinity state, as indicated by the binding site being a green square. K or Na ions that enter the entrance to the filter are bound briefly, after which they either return to the solution they came from or they cross the membrane and permeate. In the latter case, they are counted in the squares at the bottom of the lower compartment, with solid circles indicating ions that have crossed. At the end of this short simulation (1,000 steps) three K ions and six Na ions have permeated. The simulation is too short to obtain reliable statistics.     (Movie 3)  (Back)