MEMBRANE TRANSPORT PROTEINS © 2016 Paul Billiet ODWS

Passive Transport Driving forces Diffusion along a concentration gradient Electrochemical gradient: A membrane potential is set up due to a voltage (potential difference) across the membrane The cell contains a lot of negatively charged ions Positive ions are encouraged to move in and Negative ions are encouraged to move out. © 2016 Paul Billiet ODWS

Electrochemical gradient K+ +ve ECF Plasma membrane Cytoplasm Cl- -ve Positive ions are encouraged to move in and negative ions are encouraged to move out. © 2016 Paul Billiet ODWS

Diffusion and facilitated diffusion Diffusion may occur through any part of the plasma membrane or through channel proteins e.g. transport of N2 gas molecules Facilitated diffusion uses pores made of carrier proteins e.g. transport of glucose molecules. © 2016 Paul Billiet ODWS

Diffusion and facilitated diffusion Simple diffusion Rate of transport Concentration Pores saturated Facilitate diffusion © 2016 Paul Billiet ODWS

Channel Proteins Permit the passive movement of molecules or ions of appropriate size (dialysis) through an aqueous pore Simple diffusion © 2016 Paul Billiet ODWS

Potassium ion pore channel ECF Potassium ion pore channel Cytoplasm © 2016 Paul Billiet ODWS

Carrier proteins Bind to specific solutes to transport them across a membrane Facilitated diffusion Protein changes conformation © 2016 Paul Billiet ODWS

Active Transport Uses energy Faster than diffusion Can move against a concentration or electrochemical gradient Uses carrier proteins – very specific  selective transport. © 2016 Paul Billiet ODWS

Evidence of active transport in marine algal cells © 2016 Paul Billiet ODWS

Change of configuration Uniport pore One type of molecule transported Change of configuration P P P Phosphorylation Dephosophorylation ATP + H2O  ADP + Pi © 2016 Paul Billiet ODWS

Change of configuration Coupled pores Two molecules transported together Symport: Both molecules move in the same direction Change of configuration P P P Phosphorylation Dephosophorylation ATP + H2O ADP + Pi © 2016 Paul Billiet ODWS

Antiport pores Molecules move in opposite directions (one in the other out) e.g. Na+ (out) and K+ (in) © 2016 Paul Billiet ODWS

Change of configuration P Phosphorylation Change of configuration P Dephosophorylation © 2016 Paul Billiet ODWS

The Sodium-Potassium Pump