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15-1,585 Obviously ion concentration not the same inside cell as outside How is this maintained?

15-1,585 Obviously ion concentration not the same inside cell as outside How is this maintained? What is magic about these concentrations (similar for inverts, verts)??. 15-1, 579 Properties of a pure phospholipid membrane 15-33, 611 In real membranes water gets in via aquaporins.

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15-1,585 Obviously ion concentration not the same inside cell as outside How is this maintained?

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  1. 15-1,585 Obviously ion concentration not the same inside cell as outside How is this maintained? What is magic about these concentrations (similar for inverts, verts)??

  2. 15-1, 579 Properties of a pure phospholipid membrane 15-33, 611 In real membranes water gets in via aquaporins transporting epithelia (RBCs, kidney, tear ducts) poisoned by mercury not ion permeable at least 5 isoforms Ishida et al. 1996 Expression and characterization of lacrimal gland water channels in Xenopus oocytes BBRC 224:1-4 inject aquaporin cDNA into oocytes-take up water inject antisense cDNA into same eggs-stops water uptake

  3. 15-3, 581 membrane transporters that do not require ATP hydrolysis Couple a reaction that is thermodynamically favorable to one that is not Transport with same rules as enzyme kinetics 15-5, 583

  4. 15-7, 584 Glucose transporters -uniporters -7 genes, 6 proteins GLUT 1-RBC, brain, ubiquitous GLUT 2-liver GLUT 3-brain and fetal muscle GLUT 4-skeletal and cardiac muscle GLUT 5-sperm, muscle, adipocytes GLUT 6-pseudogene GLUT 7-hepatocytes Can go in either direction- concentration driven Normally glucose higher outside cell than in, but during starvation transport reverses

  5. Frozen wood frogs -upregulate glucose transporters dramatically as soon as toes freeze -freeze from outside in -thaw from inside out -highest concentration of glucose in organs

  6. Ion Concentration vs. Charge Concentration across membranes -resting potential of a cell is -70 mV (or -85 mV-depending on who you talk to)-that means the inside is negative relative to the outside - -70 mV over 3.5 nm of plasma membrane thickness = 200000 V over cm thickness -not trivial -plasma membrane is a capacitor- two conducting surfaces separated by a nonconducting material -spontaneous movement of ions (not ATP involved) determined by both concentration gradient and electrical potential across membrane

  7. At Nernst potential-concentration gradient perfectly balanced with electrical gradient (electrical potential) and ions don't flow in or out Osmolarity-total particle concentration-has to be balanced on both sides of membrane or cell will shrink or swell.

  8. Group Exercise #10 This is an old model of how ions are transported across membranes, which is now has virtually no support. Why can’t this model work?

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