Cells use transporters to move nearly all metabolites across membranes. Butt how

Question

Cells use transporters to move nearly all metabolites across membranes. Butt how much faster is a transporter than simple diffusion? There is sufficient information available for glucose transporters to make comparison. The normal circulating concentration of glucose in humans is 5 mM, whereas the intracellular concentration is usually very low (for this problem assume the internal concentration of glucose is 0 mM). At what rate (molecules/sec) would glucose diffuse into a cell if there were no transporter? The permeability coefficient of glucose is 3 x 10-8 cm/sec. Assume a cell is a sphere with a diameter of 20 um. The rate of diffusion equals the concentration difference multiplied by the permeability coefficient and the total surface area of the cell (Surface of of sphere = 4pieR2. Rememeber to convert everything to compatible units so that the rate is molecules/sec).

A. 1.1 X 106 molecules/sec

B. 2.1 X 106 molecules/sec

C. 1.1 X 107 molecules/sec

D. 2.1 x 105 molecules/sec

E. No glucose will be transported.

Explanation / Answer

A is the correct answer.

R= (5mM-0mM)*3*10^(-8)cm/sec * 4*pi*(10um)^2

convert all units and get 1.135*10^6 molecules/sec.

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