Here's one experimental approach to finding out how rapidly a membrane transporter can move its solute into the cell: combine biochemical information about how much solute accumulates in the cell over time with structural information about how many transporters are on the surface of the cell. You are studying a spherical eukaryotic cell that has a diameter of 17 ?m and is engaged in glycolysis. Its energy source is glucose, which it is taking up from its environment via Na/glucose symporters distributed throughout the surface of its plasma membrane. By briefly adding an inhibitor of all glucose breakdown, you are able to determine that glucose accumulates in the cell at the rate of 47 ?M/hr.

Based on this number, how many ?moles of glucose must be entering the cell per hour?

(Assume that one-half of the volume of the cell is composed of organelles, and thus not available for diffusion of glucose)

What is the flux of glucose into the cells (flux is expressed in moles per cm2 per sec)?

If electron microscopy indicates that there is on average 1 Na/glucose symporter per ?m2 of the plasma membrane, at what rate must each symporter transport glucose, in molecules per second?