Membrane Transport

Membrane Transport

1. Endocytosis

   • fluidity of membrane
     • allows materials to be taken in
     • allows structures surrounded by membrane to change shape and structure
   • vesicles pinched off from membranes
     • done by proteins in membrane using ATP
     • forms inside plasma membrane
     • carries materials from outside
   • contents
     • water
     • solutes
     • molecules too large to pass through membrane
     • sometimes large undigested food particles
     • sometimes pathogens to kill

2. Vesicle movement in cells

   • vesicle
     • small sac of membrane with drop of fluid inside
     • spherical
     • present in eukaryotic cells usually
     • called contractile vacuole
   • move materials within cells
   • movement of cell contents or proteins

3. Exocytosis

   • fluidity of membrane
     • allows materials to be released
     • vesicle fuses with plasma membrane; contents out of cell
     • digestive enzymes released
     • expel waste products

4. Simple diffusion

   • moves particles across membrane
   • higher concentration to lower concentration down concentration gradient
   • passive process
   • particles pass between phospholipids in membrane
   • non-polar particles enter easily
   • polar particles can enter at low rates
   • smaller the easier

5. Facilitated diffusion

   • particles move across membrane
   • particles that cannot diffuse pass through a channel in membrane
   • channels
     • holes with narrow diameter
     • protein walls
     • diameter and chemicals ensure only one type enters
   • high conc to low conc

6. Osmosis

   • particles move across membrane
   • net water movement
   • low conc solute to high conc
   • passive
   • water channels aquaporins
     • narrowest point - slightly larger than water molecules
     • positive charge prevents proton entry
   • small enough to flow freely through membrane

7. Active transport

   • particles move across membrane
   • against conc gradient
   • requires ATP
   • carried out by pump proteins
   • allows cell to control cytoplasm
   • pumped in from central chamber