BIO 365R Exam I key - Name_...

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Name_________________________ Vertebrate Physiology (BIO 365R) Thursday Feb. 19, 2009 1) (8 pts) Imagine a cell with the following intra- and extracellular ion concentrations: Intra (mM) Extra (mM) Na + 200 200 K + 200 20 Ca 2+ 10 100 Cl - 400 40 a) If the membrane were solely permeable to K + , the membrane potential would be: __________________ Vm = 58 log 20/200 = 58 log 1/10 = -58 mV b) If the membrane were solely permeable to Na + , the membrane potential would be: _________________ 0 mV c) If the membrane were solely permeable to Ca 2+ , the membrane potential would be: _________________ Vm = 58/2 log 100/10 = 26 log 10 = 26 mV d) If the membrane were solely permeable to Cl - , the membrane potential would be: ___________________ Vm = 58/-1 log 40/400 = -58 log -1 = 58 mV 2) (4 pts) Using the ion concentrations above, set up an equation (but you don’t have to solve it) that would allow you to solve for the resting potential of the cell if the membrane permeability to Na + were 10x greater than to K + and 100X greater to Na + than Cl - . V m = 58log [ Na ] o (100) +[ K ] o (10) +[ Cl ] i [ Na ] i (100) +[ K ] i (10) +[ Cl ] o or V m = 58log [ Na ] o +[ K ] o (.1) +[ Cl ] i (.01) [ Na ] i +[ K ] i (.1) +[ Cl ] o (.01) 3) (4 pts) At an ion’s equilibrium potential (circle the correct answer): a) the forces exerted by the chemical and electrical gradients are exactly opposite and equal b) the forces exerted by the chemical gradient are greater than those of the electrical gradient c) the forces exerted by the electrical gradient are greater than those of the chemical gradient 1
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Name_________________________ d) The Nernst potential is always 0 mV. 4) (5 pts) Label T for true and F for false statements. K + leakage channels have: __ F __ a non-linear I-V curve __ T __ are mainly responsible for setting resting potential __ T __ are formed by a tetramer of four subunits __ F __ have an S4 segment __ F __ are blocked by tetrodotoxin 5) (4 pts) Write the target of each drug in the space next to it. ouabain ____ Na+-K+ pump (Na+ K+ ATPase )______ TEA ______ K+ channel _____________ TTX ______ Na+ channel _____________ digitalis ___ Na+-K+ pump (Na+ K+ ATPase )__ 6) (4 pts) What causes the high levels of K + ions and low levels of Na + ions inside cells? The Na+ K+ pump pumps out Na+ ions and brings in K+ ions. 7) (2 pts) What is the equation for driving force? In your own words, what does it mean? (Vm –Eion) This is the difference between the membrane potential and the equilibrium potential for an
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BIO 365R Exam I key - Name_...

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