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Membrane Transport

Membrane Transport. 3 Types of transport. Passive Transport. Simple diffusion Small non-polar molecules No ions Examples: Fatty acids Steroids CO 2 O 2 H 2 O (?)—osmosis Only move DOWN concentration gradient. Osmosis. Osmosis, con't. Mediated Transport. Passive mediated transport

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Membrane Transport

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  1. Membrane Transport

  2. 3 Types of transport

  3. Passive Transport Simple diffusion • Small non-polar molecules • No ions • Examples: • Fatty acids • Steroids • CO2 • O2 • H2O (?)—osmosis • Only move DOWN concentration gradient

  4. Osmosis

  5. Osmosis, con't.

  6. Mediated Transport • Passive mediated transport • Facilitated diffusion • Carrier proteins • Channel proteins • DOWN a conc. gradient • Active transport • Primary active transport—uses ATP • Secondary active transport—uses a different energy source • Pumps things UP a conc. gradient

  7. How to tell mediated transport vs. simple diffusion • Saturation kinetics • Competition kinetics • Specificity

  8. Some more terms

  9. GluT1 (RBCs)—a carrier protein

  10. Channel proteins • Ion channels • Ions • Selective • Generally gated • Porins • Larger • Less specific • Aquaporins • water

  11. Porins

  12. The Pore-Forming Toxins • Lethal molecules produced by many organisms • Insert themselves into the host cell plasma membrane • Kill by • collapsing ion gradients • facilitating entry by toxic agents • introducing a harmful catalytic activity

  13. Colicins • Produced by E. coli • Inhibit growth of other bacteria (even other strains of E. coli) • Single colicin molecule can kill a host!

  14. Other Pore-Forming Toxins • Hemolysin from • Staphylococcus aureus • a symmetrical pore • Aerolysin • Aeromona hydrophila • Anthrax toxin protective antigen • Bacillus anthracis

  15. Hemolysin

  16. Ionophore Antibiotics

  17. Valinomycin • Cyclic peptide • Valinomycin-potassium complex diffuses freely and rapid across membranes

  18. Gramicidin—pore forming

  19. Active Transport

  20. Direct and Indirect AT

  21. The Na/K ATPase

  22. Consequences of Na/K ATPase • Two ion gradients • Used as energy source • Electrical signaling • Charge difference across membrane • Membrane potential difference • Negative on inside • -60 to –90 mV in animal cells • ~ -150 mV in bacteria • -200 to –300 mV in plants • Not just due to these ions • Phosphatidylserine on inside of PM • Other ions

  23. Indirect (secondary) AT • Na/glucose symporter • Intestinal absorptive cells

  24. Energetics of Transport

  25. Thermodynamics of Transport, charged

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