& Blology/Spring 2018 Page 8 of 15 Practice questions for Exam 3 50. You have pr
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& Blology/Spring 2018 Page 8 of 15 Practice questions for Exam 3 50. You have prepared lipid vesicles (spherical lipid bilayers) that contain Nnthe molecule that normay protein. All of the Na"-K' pumps are oriented faces the cytosol is in the inside of the vesicle and the portion of the moump extracellular space is on the outside of the vesicle. Assume that each direction and one K" ion in the other direction during each pumping Na-K' pump normally functions in the plasma membrane). K" pumps as the sole membrane n such a way that the portion of that normaly transports one Na" ion in one cycle (see figure below to see how the ADP Predict what would happen in each of the following conditions a) The solutions inside and outside the vesicles contain both Nat and K ions but no ATP, b) The solution outside the vesicles contains both Na' and K' ions, the soltution Inside contains both Na" c) The solution outside contains Na*; the solution inside contains Na" and ATP and K-ions and ATP. For a particular cell, the concentration of sucrose is 10 mM on the inside of the cell and 0.5 mM on the outside, whereas [Na'] is 0.5 mM on the inside of the cel and 10 mM on the outside. The membrane potential is-150 mV, and the temperature is 25'C IS1, Constants: R 1.987 cal/mok T-25C 298 K a) What is the AG for the inward transport of sucrose? b) What is the &G; for the inward transport of Na"? What would be the net AG for the coupling of these two reactions? c) 52. The bacterium Brucella abortus can utlize the tetrose erythritol as a carbon source. The concentration of erythritol within a B abortus cell is 10 mM, while the external erythritol concentration is at levels as low as 0.20 mM. What is the energy requirement for the inward transport of erythritol at 37"C under these conditions? Hint: You may use the equation below. Hint: In this case, T 37 C 310 K a) AGmad2,409.7 cal/mol c) AG1,046.5 cal/mol d) AG-1,046.5 calmolExplanation / Answer
Answer to Q50
a) If the ATP is not present, the Na+-K+ pump will not work because ATP binding provides the confirmation to which Na+ binds and so it is essential for pump to perform its activity. No ions will be transported in either direction.
b) If Na+, K+ and ATP, all three are present then the pump will operate. For each hydrolyzed ATP, one Na+ is transported out and one K+ is transported inside the cell.
c) As solution inside contains Na+ and ATP, the pump will start functioning. On ATP hydrolysis, the Na+ would be released from phosphorylated pump. Now, as no K+ ions are present outside, the pump will stop working after transporting a single Na+.
Answer to Q 51
?Ginward = RT ln[(Sinside)/(Soutside)]
a) ?Ginward for sucrose
?Ginward = 1.987 x 298 ln[(10)/(0.5)]
?Ginward = 592.126 ln(20)
?Ginward = 592.126 x 2.9957
?Ginward = 1773.831 cal/mol
b) ?Ginward for sodium
?Ginward = 1.987 x 298 ln[(0.5)/(10)]
?Ginward = 592.126 (-2.9957)
?Ginward = -1773.831 cal/mol
Answer to Ques 52
?Ginward = RT ln[(Sinside)/(Soutside)]
?Ginward = 1.987 x 310 ln[(10)/(0.20)]
?Ginward = 615.97 (1.69897)
?Ginward = 1046.51 cal/mol
Correct option is Option C
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