Beng 130 Lecture Review 14-18

Beng 130 Lecture Review 14-18 - Membrane Transport •...

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Unformatted text preview: Membrane Transport • Lipids and Biological Membranes- Amphiphilic lipid molecules- Lipid bilayers- Biological membranes • Membrane transport processes- Thermodynamic basis and overview • Nernst Equation- Diffusion potential- Electrochemical potential • Osmosis - Osmolarity- Osmotic pressure – Van’t Hoff equation- Donnan Effect and Donnan Potential • Transport across membranes- Passive transport by diffussion- Active transport BENG 130 Lectures 14&15 Reading: Chapter 5 and Lecture Notes Lipids – Amphiphilic Molecules Phospholipid (phosphitidylcholine) Cholesterol FIGURE 2–7 Amphipathic compounds in aqueous solution. (a) Longchain fatty acids have very hydrophobic alkyl chains, each of which is surrounded by a layer of highly ordered water molecules. (b) By clustering together in micelles, the fatty acid molecules expose the smallest possible hydrophobic surface area to the water, and fewer water molecules are required in the shell of ordered water. The energy gained by freeing immobilized water molecules stabilizes the micelle. Hydrophobic Effect: Self Assembly of Lipid Molecules in Water The Thermodynamic Basis of Membrane Transport • Movement of charged/hydrophilic solutes across membranes involves a desolvation process with a very high activation energy. • The activation energy for translocation of a polar solute across the bilayer is so large that pure lipid bilayers are virtually impermeable to polar/charged species. • Transporters are essential for transporting them across the bilayers. A A Osmosis and Osmotic Pressure semipermeable elastic barrier solution solvent For very dilute solution, RT V n n A A B = Π V V n A A = cRT = Π (Van’t Hoff Equation) Osmolarity • In order to really understand the concentration difference of water we should get a measure of all the free particles in solution. • To do this let us define the term osmolarity. - 1 M solution of glucose has 1 Osm. - 1 M solution of NaCl has 2 Osm (1 M Na + + 1 M Cl- ). • The higher the osmolarity of a solution the lower the concentration of water. Note: solutions of 1) 300 mM glucose 2) 150 mM NaCl 3) 100 mM glucose + 100 mM NaCl 4) 75 mM NaCl + 75 mM KCl All have the same osmolarity of 300 mOsm Osmotic Pressure How to extract fresh water from sea water? Density of sea water is about 1025 kg/m 3 . The average salinility of sea water is about 3.5% (~0.6 M NaCl + other salts). So C total = 1.2 Osm ≈ 1 M Osm At equilibrium at the membrane a the bottom of the tank: Π = − in out P P ) ( ) ( ' ' = Π − + − + h g P h g P atm atm ρ ρ Fresh water Semi-permeable membrane sea water P atm = 1 atm h = ? C total = 1 M Osm ' h m 1 h so tank, m 1 m 1 m 1 a in water of m 1 get Want to ' 3 = × × Π + = ' ' h g h g ρ ρ ∴ Osmotic Pressure Π + = ' ' h g h g ρ ρ m 250 kgm 1025 ms 9.8 s m kg 10 1.013 298 0.08205 1 kgm 1025 ms 9.8 s m kg 10 1.013 298 0.08205 1 m 1 kgm 1000 ms 9.8 )/ ( 3- 2- 2- 5 3- 2- 2- 5 3- 2- ' ' ≈ × × × × × ≈ × × × × ×...
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This homework help was uploaded on 04/07/2008 for the course BENG 130, 103B, taught by Professor Gough during the Spring '08 term at UCSD.

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Beng 130 Lecture Review 14-18 - Membrane Transport •...

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