Beng 130 Lecture 14 & 15

Beng 130 Lecture 14 & 15 - Membrane Transport • Lipids...

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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 15&16 Reading: Chapter 5 and Lecture Notes Membranes in Cells Ion Concentrations Inside and Outside of a Cell 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 Structures Formed by Lipid Molecules Liposome Structure – Thermodynamically Stable Fluid Mosaic Model of Membrane Structure Model STM Structure 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. Membrane Transport: Summary of Transport Types Transport of solutes across a membrane Protein Channels: Water and Ion Channels http://nobelprize.org/chemistry/laureates/2003/public.html Na +-K + ATPase Maintains Intracellular Concentrations of Na + and K + and Generates Electrical Potential in Cells To maintain the electrical potential of 50-70 mV which is the characteristic in most animal cells and essential for conduction of action potential in neurons, ~ 25% of total energy is consumed in the process for a human at rest. This is important in maintaining osmotic balance and volume of cells as well. Both the insides and outsides of cells contain ions. For charged particles, the driving force for diffusion is made up of two components: 1. A difference in concentration 2. The presence of an electric field Diffusion of Electrolytes Even though there is no concentration gradient, Na + will migrate towards the cathode and Cl- toward the anode due to the force imposed on the ions by an electric field....
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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 14 & 15 - Membrane Transport • Lipids...

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