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Jordan Sullivan Week 1, Winter 2009 BIPN 100 Section Friday 10:00am (Solis 109) HEY EVERYBODY… HERE’S THE ANSWER SHEET FOR THIS PAST SECTION’S HANDOUT. HOPEFULLY YOU DID THE PROBLEMS THAT WE DIDN’T FINISH ON YOUR OWN… IF NOT THEN I RECOMMEND YOU DO THIS BEFORE LOOKING AT THE ANSWERS. THERE ARE TWO QUESTIONS ON HERE THAT I HIGHLIGHTED IN GREEN… THESE ARE THE TWO QUESTIONS THAT I FELT I DIDN’T EXPLAIN VERY WELL IN SECTION, SO I WROTE A DETAILED SUMMARY ON THE ANSWERS FOR THOSE TWO QUESTIONS. ALL THE OTHER ANSWERS ARE WRITTEN IN RED. ALSO, SOMEBODY ASKED WHAT HAPPENS WHEN USING Ca 2+ IN THE GOLDMAN EQUATION… I LOOKED IT UP AND I FOUND THAT YOU WOULD WRITE IT THE SAME AS YOU WOULD K+ OR Na+, EXCEPT THAT YOU WOULD SQUARE THE CONCENTRA- TIONS OF Ca 2+ ON BOTH THE TOP AND BOTTOM. I REALLY WOULDN’T WORRY ABOUT THIS, HOWEVER… IN OTHER WORDS, THIS IS JUST F.Y.I.! Vm = 61xlog{ (P K + [K + out ]+ P Na + [Na + out ]) + P Ca 2+ [Ca 2+ out ] 2 ) /(P K + [K + in ]+ P Na + [Na + in ] + P Ca 2+ [Ca 2+ in ] 2 ) } SEE YOU NEXT FRIDAY! - JORDAN

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Problem Set: 1) Write out the mechanism of the Na + /K + -ATPase (IN = inside of cell; OUT = outside of cell). Be sure to include direction of ion flow, and the energy source used. IN | OUT | | | | | | | | | | | | 3Na(in) + 2K(out) + ATP “ADP + Pi” + 2K(in) + 3Na(out) 2) In order to transfer amino acids across intestinal epithelial cells, the cell membranes must get creative. Given that the inside of the cell has a higher amino acid concentration than either the gut lumen or the ECF, and that a Na+ cotransport is used as the power source, come up with a plausible pathway for getting Na+ through the intestinal epithelial cells and into the ECF (which leads to the bloodstream) [See drawing on board for help; See Figure 21-17 for the actual pathway… Also note that you don’t have to memorize this specific pathway, just get the feeling of what’s going on!] See Figure 21-17 in Silverthorn Book for answer 3) Two glass beakers connected by a semipermeable barrier are filled with water and different concentrations of solutes. For the following experiments determine which way water will flow (Note: All concentrations listed below are in units of milliosmolar) 1) Experiment 1 Beaker A: [Na+] = 40, [K+] = 0 Beaker B: [Na+] = 0, [K+] = 40
Ion Permeabilities: Only H2O is permeable Water will not flow because the two beakers are isoosmotic! 2) Experiment 2 Beaker A: [Na+] = 40, [K+] = 0 Beaker B: [Na+] = 0, [K+] = 40 Permeabilities: Na+ is permeable Na+ will flow down its concentration gradient (From A B)and water will follow it by osmosis! Thus, water will flow into Beaker B from Beaker A! 3) Experiment 3

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