Week 1, Lecture 3, Cell Membranes

Week 1, Lecture 3, Cell Membranes - B I O L O G Y 0 2 3...

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Unformatted text preview: B I O L O G Y 0 2 3 30-Dec-09 Gardiner 1 Cell Membranes Membrane Function 1. Be protective 2. Regulate transport 3. Signal transduction 4. Cell recognition 5. Provide anchoring sites 6. Help compartmentalize 7. Provide stable site for enzyme binding 8. Regulate fusion via junctions 9. All directed organelle motility The proteins in the plasma membrane may provide a variety of major cell functions. Fig. 8.9 B I O L O G Y 0 2 3 30-Dec-09 Gardiner 8 Phospholipids Phosphate group gives lipid a polar head ( hydrophilic water loving) Fatty acids are hydrophobic (water-fearing) In water phospholipids form a bilayer = membrane : polar group facing out, fatty acids in. Complex Lipids phospholipids-phosphate group-glycerol-two fatty acids Hydrophilic head Hydrophobic tails Figure 5.4 Phospholipid Membrane Fig. 5.4 Fig. 6.7 Membrane molecules are held in place by relatively weak hydrophobic interactions. Most of the lipids and some proteins can drift laterally in the plane of the membrane, but rarely flip-flop from one layer to the other. Membranes are fluid The lateral movements of phospholipids are rapid, about 2 microns per second. Many larger membrane proteins move more slowly but do drift. Some proteins move in very directed manner, perhaps guided/driven by the motor proteins attached to the cytoskeleton. Other proteins never move, anchored by the cytoskeleton. Fig. 5.2 Fluidity is influenced by temperature and by its constituents. As temperatures cool, fluid solid state Membranes rich in unsaturated fatty acids are more fluid that those dominated by saturated fatty acids Fig. 5.5 B I O L O G Y 0 2 3 30-Dec-09 Gardiner 16 Cholesterol amount may vary with the type of membrane Plasma - one cholesterol per phospholipid molecule Other membranes (like those around bacteria) have no cholesterol Fig. 5.7 To work properly with active enzymes and appropriate permeability, membrane must be fluid, about as fluid as salad oil....
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This note was uploaded on 04/18/2010 for the course BIOLOGY 1223 taught by Professor Gardiner/lajoie during the Fall '09 term at UWO.

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Week 1, Lecture 3, Cell Membranes - B I O L O G Y 0 2 3...

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