sample_midterm_1_2005_key

sample_midterm_1_2005_key - YOUR NAME_ Student ID#_ MIDTERM...

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YOUR NAME__________________________ Student ID#_________________ 1 NPB 100 MIDTERM 1 SPRING, 2005 Your signature______________________ Question Score Total 1 6 2 7 3 10 4 6 5 18 6 5 7 20 8 20 9 8 TOTAL 100
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YOUR NAME__________________________ Student ID#_________________ 2 Question 1. (6 points) At which point(s) in this action potential is the cell’s membrane more permeable to potassium than it is to sodium? CIRCLE AS MANY ANSWERS AS ARE CORRECT! A B C D Question 2. (7 points) Ouabain is a toxin that prevents the Na + /K + ATPase from working. 2a. (3 points) You apply ouabain to a cell with a resting membrane potential of –60 mV, and you wait several hours. This will have which effect on the cell’s membrane potential? CIRCLE ONE ANSWER: depolarize hyperpolarize no effect 2b. (4 points) Explain your answer to question 4a. The Na + /K + ATPase is what sets up the concentration gradients of sodium and potassium which underlie the cells membrane potential. Without this pump, the concentration gradients run down until equal concentrations of both sodium and potassium are found inside and outside the cell. This causes the cell’s membrane potential to go to approximately 0 mV (if only sodium and potassium were involved in the membrane potential it would go to exactly 0 mV. From the GHK equation if only sodium and potassium are involved you would get ln(1) which is 0. Since chloride has a small contribution to the resting membrane potential, it will not go exactly to 0). 0 mV is more positive than –60 mV, so this change in potential is a depolarization. GO ON TO THE NEXT PAGE!
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YOUR NAME__________________________ Student ID#_________________ 3 Question 3. (10 points) You are studying a cell with no chloride transporters or exchangers. The resting membrane potential of this cell is -65 mV. Remember that log 0.01= -2, log(0.1) = -1, log(1) = 0, log(10) = 1, log(100) =2, log(1000)=3 3a. (5 points) What is the equilibrium potential for chloride? Explain your answer. -65mV If there are no transporters or exchangers, the cell cannot regulate the concentrations of chloride inside and outside the cell. Therefore the driving force on chloride will move chloride ions until the concentrations are such that the equilibrium potential for chloride will equal the resting membrane potential of the cell.
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sample_midterm_1_2005_key - YOUR NAME_ Student ID#_ MIDTERM...

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