Membrane Transport

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

5. Osmosis

6. Osmosis, con't.

7. 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

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

9. Some more terms

10. GluT1 (RBCs)—a carrier protein

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

12. Porins

13. 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

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

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

17. Hemolysin

18. Ionophore Antibiotics

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

20. Gramicidin—pore forming

22. Active Transport

23. Direct and Indirect AT

25. The Na/K ATPase

27. 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

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

31. Energetics of Transport

32. Thermodynamics of Transport, charged