Lecture 7 (Sept 12)

Lecture 7 (Sept 12) - Biological Sciences 110A:...

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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 C e ll m o tility a nd m o rpho lo g y Me m b rane  fis s io n a nd fus io n  Intrac e llula r ve s ic le  tra ffic king Lo c a liza tio n a nd func tio n                                              o f m e m b ra ne  pro te ins Fig . 4.24 Ka rp
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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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Lecture 7 (Sept 12) - Biological Sciences 110A:...

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