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Exam 1 Key

Exam 1 Key - Name Pg 1 First Exam BIO 365R Spring 2008...

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Name_______________________________ Pg. 1 First Exam- BIO 365R- Spring 2008 PLEASE NOTE THAT THERE WERE TWO VERSIONS OF THE EXAM, WHILE SIMILAR, THE ANSWERS TO SOME QUESTIONS WERE DIFFERENT. 1) (8pts) You discover a new life form on Mars. It has the following ions in its extracellular fluids: strontium (Sr + ), Rubidium (Rb + ), fluorine (Fl - ). These are in the following concentrations. Extracellular (mM) Intracellular (mM) Extracellular (mM) Intracellular (mM) Sr + 10 1000 1000 10 Rb + 1000 100 100 1000 Fl - 500 500 500 500 What is the resting potential of their neurons if it is solely due to a conductance to Sr + ? V m = 58log 10 1000 = 58log 1 100 = 58log(0.01) = 58( " 2) = " 116 mV V m = 58log 1000 10 = 58log 100 1 = 58log(100) = 58(2) = 116 mV What is the resting potential of their neurons if it is solely due to a conductance to Rb + ? V m = 58log 1000 100 = 58log 10 1 = 58log(10) = 58(1) = 58 mV V m = 58log 100 1000 = 58log 1 10 = 58log(0.1) = 58( " 1) = " 58 mV What is the resting potential of their neurons if it is solely due to a conductance to Fl - ? V m = 58 " 1 log 500 500 = " 58log 1 1 = " 58log(1) = " 58(0) = 0 mV What is the resting potential of their neurons if the membranes are two times more permeable to Sr + than Rb + ? V m = 58log 1000 + 100 10 + 1000 = 58log 1100 1010 = 58log(1.09) = 58(0.037) = 2.2 mV What is the resting potential of their neurons if the membranes are equally permeable to Sr + and Rb + ? V m = 58log 10(2) + 1000 1000(2) + 100 = 58log 1020 2100 = 58log(0.49) = 58( " 0.31) = " 18 mV 2) (2 pts) During kidney failure extracellular K + levels become elevated. This hyperpolarizes/depolarizes (circle one) all excitable cells. 3) (4 pts) What is the definition of driving force? You may write it in words or in an equation. Driving force = V m - E ion

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Name_______________________________ Pg. 2 4) (4 pts) Explain why the action potential can never become more negative than E K . If any more K + were to leave the cell going down its concentration gradient, the electrical gradient would oppose it and pull it back in because it is more negative. Explain why the action potential can never become more positive than E Na . At E Na if any Na + entered the cell it would be pushed back by the electrical gradient. 5) (6 pts) True/False. Write in the space in front of each statement T if the statement is true, and F if the statement is false. [NOTE: The order and content of these questions was not the same for both versions, please read them carefully.] F The equilibrium potential for an ion is the point at which the force of the concentration gradient on an ion is twice the force of the electrical gradient. F The driving force on Na + is greater at – 70 mV than it is at +20 mV. T The driving force on K + is greater at – 70 mV than it is at +20 mV. T Prolonged depolarization causes voltage-dependent Na + channels to inactivate. F Refractory period is due to the inactivation of both Na + and K + channels.
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