The Na^+ -glucose symport system of intestinal epithelial cells couples the \"do
ID: 475132 • Letter: T
Question
The Na^+ -glucose symport system of intestinal epithelial cells couples the "downhill" transport of two Na^+ ions into the cell to the "uphill" transport of glucose, pumping glucose into the cell against its concentration gradient. If the Na^+ concentration outside the cell ([Na^+]_out) is 149 mM and that inside the cell ((Na^+]_in) is 19.0 mM, and the cell potential is -55.0 mV (inside negative), calculate the maximum ratio of [glucose]_in to [glucose]_out that could theoretically be produced if the energy coupling were 100% efficient. Assume the temperature is 37 degree C.Explanation / Answer
Use gas constant of 8.3145, and converted the temp to kelvin (ended up with 310.15), and a Faraday constant of (96.5 kJ/(mol·V)
deltaGchem=- RTln([Na+in]/[Na+out])
We know the values of Na+in and Na+out as 19mM and 149 mM
delta Gchem = 5310.93 J
DeltaGelec= - zFdelta membrane potential,
z = No of ions
delta Gelec = 10.615 KJ
Then added the two values, and used the
delta G = 10.615 KJ + 5310.93 J
15925.93 =- RTln([glucose in]/[glucose out])
([glucose in]/[glucose out]) = 2.078*10^-3