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Transcript
Membrane Transport 3 Types of transport Passive Transport Simple diffusion – Small non-polar molecules • No ions – Examples: • • • • • Fatty acids Steroids CO2 O2 H2O (?)—osmosis – Only move DOWN concentration gradient Osmosis Osmosis, con't. 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 How to tell mediated transport vs. simple diffusion • Saturation kinetics • Competition kinetics • Specificity Some more terms GluT1 (RBCs)—a carrier protein Channel proteins • Ion channels – Ions – Selective – Generally gated • Porins – Larger – Less specific • Aquaporins – water Porins 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 Colicins • Produced by E. coli • Inhibit growth of other bacteria (even other strains of E. coli) • Single colicin molecule can kill a host! Other Pore-Forming Toxins • Hemolysin from – Staphylococcus aureus – a symmetrical pore • Aerolysin – Aeromona hydrophila • Anthrax toxin protective antigen – Bacillus anthracis Hemolysin Ionophore Antibiotics Valinomycin • Cyclic peptide • Valinomycinpotassium complex diffuses freely and rapid across membranes Gramicidin—pore forming Active Transport Direct and Indirect AT The Na/K ATPase 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 Indirect (secondary) AT • Na/glucose symporter – Intestinal absorptive cells Energetics of Transport Ain Aout GA = RT ln ([A]in/[A]out) if [A]out>[A]in, then G<0 for inward movement Thermodynamics of Transport, charged GA = RT ln ([A]in/[A]out) + ZAF Z= charge on A F = Faraday's constant, the charge in a mole of electrons = membrane potential, difference in charge between in and out, generally negative