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Homework 1 key - Homework 1 1 You are studying a cell with...

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Homework 1 1) You are studying a cell with the following intracellular and extracellular ionic concentrations (mM): Ion Extracellular Intracellular Sodium 100 10 Potassium 10 100 Chloride 100 10 Membrane permeabilities are as follows: Sodium: 10 Potassium: 100 Chloride: 10 The cell is at room temperature. Using this information, answer the following questions: A) What is the equilibrium potential for chloride? Using the Nernst equation, E = -58log (100/10) = -58 mV cl Using the GHK equation, V =58log((100X10 + 10X100 + 10X10)/(100X100 + 10X10 + 10X100) m V =58log(2100/11100) = 58log(0.189) = -41.9 mV m The resting membrane potential is less negative than the chloride equilibrium potential. Therefore, at rest chloride will be driven into the cell (trying to make the inside of the cell closer to the chloride equilibrium potential) so the transporter must move chloride out of the cell in order to maintain the chloride concentration. B) What is the resting membrane potential of the cell? C) This cell has a chloride transporter which maintains the chloride concentration inside the cell. Which direction does the transporter move chloride across the membrane?
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D) There are no ions present in this system other than potassium, sodium, chloride and organic anions.
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