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 –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 Valinomycin- potassium 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

Thermodynamics of Transport, charged