Lecture 7 (Sept 9)

Lecture 7 (Sept 9) - Biological S nce 110A: I ntroduction...

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Lecture 7: Membrane properties and membrane transport Regulation of membrane fluidity Diffusion of proteins in the membrane Passive diffusion vs. facilitated transport Ion channels and carrier proteins ATPase transporters: Na+/K+ pump Co-transport/secondary active transport Regulation of osmosis Regulation of glucose uptake Biological Sciences 110A: Introduction to Biology Kendal Broadie Reading in Chapter 4 (136-150) Karp
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The fluid mosaic model of cellular membranes Lipid bilayer ~ 4.5 nm Membrane proteins 1. Rapid rotation about lipid axis 2. Rapid lateral diffusion (random walk) in membrane plane: ~2 μ m in 1 sec rate: 10 -6 sec 3. Flip flop extremely slow: rate: 10 5 sec (<1 event/month) Membrane fluidity is vital Cell motility and morphology Membrane fission and fusion Intracellular vesicle trafficking Localization and function of membrane proteins Fig. 4.24 Karp
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Fluid membrane Membrane fluidity is temperature dependent At normal physiological temperatures, cell membranes are fluid Rotational Translational Flexibility Fig. 4.21 Karp
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Crystallized membrane Membrane fluidity is temperature dependent This is very bad! Cooling cells (to 0-4 o C) slows or halts many functions dependent on membrane fluidity Cells use three strategies to regulate membrane fluidity: 1. Alter length of lipid tails (all) 2. Alter saturation of lipid tails (all) 3. Cholesterol (animals) At low temperature, the hydrocarbon tails of membrane lipids “congeal” into what can be described as a crystalline gel At normal physiological temperatures, cell membranes are fluid Rotational Translational Flexibility Fig. 4.21 Karp
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Proteins diffuse in the plane of the membrane F luorescence R ecovery A fter P hotobleaching (FRAP) 1. Fluorescently label membrane protein in living cell 2. Photobleach patch or with laser beam: irreversibly destroys fluorophore 3. Monitor recovery of fluorescence (Why does fluorescence recover?) 4. Recovery rate is a measure of lateral diffusion of labeled protein Photobleach T is a measure of diffusion rate Fluorescent intensity Elapsed time (sec) 0 Many proteins freely diffuse Protein diffusion is slower than lipids Unbleached protein diffuses from surrounding areas Fig. 4.25, 4.26 Karp
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This note was uploaded on 01/04/2010 for the course BSCI BSCI 110A taught by Professor Zwiebel during the Spring '09 term at Vanderbilt.

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Lecture 7 (Sept 9) - Biological S nce 110A: I ntroduction...

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