The Open Door Web Site
Membrane Transport Proteins
Passive Transport - Facilitated diffusion
The difference between diffusion and facilitated diffusion.
Diffusion may occur through any part of the plasma membrane, e.g. N2 gas molecules.
Facilitated diffusion uses pores, e.g. glucose molecules
Types of pore
Carrier proteins: Bind to specific solutes to transport them across a membrane
Uniport pore: One type of molecule transported
Coupled pores: Two molecules transported together
Symport: Both molecules move in the same direction eg Glucose and Na+ in the kidney and intestine epithelial cells.
Antiport: Molecules move in opposite directions (one in the other out), eg 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.
Exocytosis and Endocytosis
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.
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.
The Open Door Web Site is non-profit making. Your donations help towards the cost of maintaining this free service on-line.
Donate to the Open Door Web Site using PayPal