MEMBRANE TRANSPORT PROTEINS © 2010 Paul Billiet ODWSODWS

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 Positive ions are encouraged to move in and Negative ions are encouraged to move out © 2010 Paul Billiet ODWSODWS

Electrochemical gradient ECF +ve Cytoplasm -ve Plasma membrane K+K+ Cl - Positive ions are encouraged to move in and negative ins are encouraged to move out © 2010 Paul Billiet ODWSODWS

Diffusion and facilitated diffusion Diffusion may occur through any part of the plasma membrane, e.g. N 2 gas molecules. Facilitated diffusion uses pores, e.g. glucose molecules © 2010 Paul Billiet ODWSODWS

Diffusion and facilitated diffusion Facilitate diffusion Pores saturated Rate of transport Concentration Simple diffusion © 2010 Paul Billiet ODWSODWS

Channel Proteins Permit the passive movement of molecules or ions of appropriate size (dialysis) through an aqueous pore © 2010 Paul Billiet ODWSODWS

Carrier proteins Bind to specific solutes to transport them across a membrane © 2010 Paul Billiet ODWSODWS

Active Transport Uses energy Faster than diffusion Can move against a concentration or electrochemical gradient Uses carrier proteins – very specific  selective transport © 2010 Paul Billiet ODWSODWS

Evidence of active transport in marine algal cells © 2010 Paul Billiet ODWSODWS

Uniport pore One type of molecule transported Change of configuration Phosphorylation ATP + H 2 O  ADP + Pi Dephosophorylation P P P © 2010 Paul Billiet ODWSODWS

Coupled pores Two molecules transported together Symport: Both molecules move in the same direction Phosphorylation Change of configuration ATP + H 2 O  ADP + Pi Dephosophorylation P P P

Antiport pores Molecules move in opposite directions (one in the other out) e.g. Na + (out) and K + (in) ATPase is an antiport pore protein ATP is made on the mitochondria inner membranes by throwing an ATPase into reverse

Dephosophorylation Phosphorylation Change of configuration P P P P P P

Exocytosis and Endocytosis Transferring large molecules or particles or large volumes in and out of the cell Mediated by special proteins Endocytosis may form small vesicles by invaginating the plasma membrane = Pinocytosis Endocytosis may also occur when a large cell flows round and engulfs a smaller cell = Phagocytosis. © 2010 Paul Billiet ODWSODWS

ExocytosisEndocytosis Two bilayers of phospholipid touch Bilayer adherence Two bilayers fuse Bilayer joining ECF Cytoplasm Invagination ECF Cytoplasm Secretion © 2010 Paul Billiet ODWSODWS

Exocytosis and Endocytosis Exocytosis may be continuous as a cell makes material for secretion Exocytosis may be regulated, vesicles are stored in the cytoplasm waiting for a signal to be released Endocytosis uses protein coated pits which form coated vesicles The plasma membrane has receptor molecules on the outer surface When the specific molecule attaches to the receptors the membrane invaginates © 2010 Paul Billiet ODWSODWS

Phagocytosis Also works using receptor molecules Phagocytic white blood cells (neutrophils and macrophages) recognise and engulf microbes this way Pseudopod © 2010 Paul Billiet ODWSODWS

Phagocytosis Contact with prey Receptor molecules on the plasma membrane recognise surface antigens © 2010 Paul Billiet ODWSODWS

Phagocytosis Feeding cup forms to engulf the prey The membrane stays in contact with the prey © 2010 Paul Billiet ODWSODWS

Phagocytosis Bilayer adherance © 2010 Paul Billiet ODWSODWS

Phagocytosis Bilayers fuse Food vacuole forms Lysosomes fuse with it The prey is digested Food vacuole © 2010 Paul Billiet ODWSODWS