Hanna Week 3 Key - IA Hanna Tran [email protected] Section...

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IA: Hanna Tran Section: Tue 6-6:50 APM 2301 [email protected] OH: Wed 1PM Hi Thai BIPN 100 PROBLEM SET: WEEK 3 Topics: Membrane Potential and Ion Concentration Nernst Equation Goldman-Hodgkin-Katz Equation Ionic Currents and Ohm’s Law Graded vs. Action Potentials MEMBRANE POTENTIAL AND ION CONCENTRATION 1. Draw a cell and label the relative concentration gradients of K + , Na + , Ca 2+ , Cl - , and protein 2. What is a membrane potential (V m )? What is the unit? How is it established? Membrane potential (V m ) : electrical potential between the intra- and extracellular compartments Units: mV Membrane potential is established when ions move down their concentration gradients, resulting in a build up of electrical potential. The abundant expression of K + leak channels has the most influence on the membrane potential, resulting in the negative resting potential. 3. As a result of the Na + K + ATPase, the inside of the cell has a net __________ (positive/ negative ) charge and the outside of the cell has a net __________ ( positive /negative). (Hint: the net reaction equation – the result is 3 Na+ ions go out of the cell and 2 K+ ions go in.) NERNST EQUATION 4. What is the equilibrium potential of an ion (E ion )? What is the unit? Equilibrium potential (E ion ): membrane potential at which the concentration gradient and electrical potential are in equilibrium – essentially the net flow between open channels is 0. Units: mV 5. (a) Write out the Nernst Equation. Define the variables. E ion = RT ln[ion] out zF [ion] in K + Na + Cl - Ca 2+ Protein (A - ) Extracellular space Intracellular space K + Na + Cl - Ca 2+ Protein (A - ) 1
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IA: Hanna Tran Section: Tue 6-6:50 APM 2301 [email protected] OH: Wed 1PM Hi Thai R = universal gas constant z = charge T = absolute temperature (K) F = Faraday’s constant. (b) Write out the simplified Nernst equation. (They need to memorize this!) E ion = 61 log[ion] out z [ion] in 6. Fill in the middle two columns of the chart below with the normal concentrations of each ion at physiological conditions (T = 37C), and then calculate each equilibrium potential for each ion. You can
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