The Na+/glucose symport transports glucose from the lumen of the small intestine into cells lining the lumen. Transport of 1 glucose molecule is directly coupled to the transport of 1 Na+ ion into the cell.

Assume the following conditions at 37 °C: [Na+]in = 12 mM, [Na+]out = 145 mM, [glucose]out = 28 μM, and ˆ†( = - 72 mV (inside negative).
a. What is ˆ†G for transport of Na+ from outside to inside under these conditions?
b. What is the upper limit for [glucose]in under these conditions?
c. Which of the two hypothetical symports shown below (A or B) would achieve the highest concentration of [glucose]in under the conditions described above? Briefly explain your choice.

Transcribed Image Text:

1 Na out1 glucoseout Nn1 glucosen A: 1 Na out + 2 glucose,out → 1 Nain + 2 glucose,n B: 2 Na out + 1 glucoseout → 2 Nain+ 1 glucose,n