1. Membrane Transport Structure of Biological Membranes
Diffusion and Fick’s First Law
Partition Coefficients and Movement
Osmosis and Osmotic Movement
Charge Gradients Across the Membrane
Donnan Equilibrium
Passive Transport
Straight Diffusion
Facilitated Diffusion -- Cystic Fibrosis
Active Transport -- Na/K ATPase
Coupled Transport

2. Membrane Protein/Lipid Ratio
Myelin
Plama Membrane
Liver Cell
Intestinal cell 4.6
RBC Ghost
E.R
Size
Plasma Membrane 9-10 nm
Mitochondria outer nm
Golgi 8 nm

4. Membrane Lipids
Membranes vary in thickness but all appear to be lipid bilayers
Components-- phosphoglycerides, sphingolipids and cholesterol
Cholesterol stabilizes membrane
40%-60% lipid by weight
Most common lipid phosphatidylcholine

8. Osmosis
Osmosis is the special case of the diffusion of water across a membrane
Osmosis = Gas constant x absolute temperature x concentration gradient
p = CRT where C = concentration in moles l-1; R = gas constant of .082 l atm/Ko-1 mole-1;T= temperature

9. Water Movement Diffusive water movement is much less than osmotic flux
Water pores have been postulated by never documented
Diffusion may be limited by unstirred layers on either side of the membrane

13. Crossing Membranes Diffusion Diffusion shows linear kinetics
Fick’s First Law Revisited
Rate = DA [C]/x or the amount of a substance crossing the membrane per unit time = the diffusion coefficient (cm2/sec) x area of the membrane (cm2) x the concentration gradient (moles/cm3)/ the thickness of the membrane (cm)
Diffusion shows linear kinetics

14. Permeability
The permeability coefficient in units of cm-sec is a measure of how easily a substance penetrates and crosses the membrane
Solutes must break hydrogen bonds with water, move into the lipid phase and cross to an aqueous phase
Solute charge, size of molecule, temperature and membrane type all determine permeability

16. Donnan Equilibrium
Both concentration gradients and charge gradients contribute to the distribution of ions on either side of a membrane
If one side of the membrane contains a charge impermeant solute like protein, the concentrations of the permeant ions on either side will not be equal

19. Transport Types Straight Diffusion
Facilitated Diffusion through a protein channel or pore
Active transport
Coupled Transport

21. Facilitated Diffusion
Movement is through a protein based channel in the membrane
Diffusion is greater than it would be without the channel
The chloride channel in cystic fibrosis is a good example of a regulated channel
Facilitated diffusion displays saturation kinetics

25. Coupled Transport
In coupled transport, an actively established ion gradient is used to drive the movement of another solute
Example: sugar and amino acid uptake in the small intestine is linked to uptake of Na which depends upon a favorable gradient created by Na/K ATPase