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Membranes

Membranes. Membrane Functions. A Bit of History. Charles Overton—1890’s Lipid nature of membranes Lipids readily crossed the membrane Polar/charged molecules did not Irving Langmuir—1900’s Phospholipid monolayer. E. Gorter and F. Grendel—1925 RBCs Lipid bilayer

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Membranes

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  1. Membranes

  2. Membrane Functions

  3. A Bit of History • Charles Overton—1890’s • Lipid nature of membranes • Lipids readily crossed the membrane • Polar/charged molecules did not • Irving Langmuir—1900’s • Phospholipid monolayer

  4. E. Gorter and F. Grendel—1925 • RBCs • Lipid bilayer Lipid bilayer was not enough to describe differential permeability • Hugh Davson and James Danielli—1935 • Protein-lipid "sandwich"

  5. Electron microscope—1950s • Organelles have membranes too • Membranes have trilaminar appearance • J. David Robertson—1960 • "unit membrane" theory • Basically extension of "sandwich" to all membranes

  6. Problems with this theory • Artificial membranes (no protein) look same under EM • Doesn't explain different ratios of lipid/protein in different membranes • Most membrane proteins are globular, not in sheets

  7. Fluid Mosaic Model • S. Jonathan Singer and Garth Nicolson—1972 • Lipid bilayer (fluid) • Mosaic of proteins floating in the lipids • Richard Henderson and Nigel Unwin—1975 • Structure of membrane-bound protein • Went through the membrane (not just on surface)

  8. The Lipids of Membranes • Phospholipids • Glycolipids • Sterols

  9. Different membranes, different lipids Differ between layers of the bilayer--assymetric

  10. Lipid Movement

  11. Evidence for fluidity

  12. Photobleaching

  13. Laser tweezers

  14. Maintaining Fluidity • Fatty acid type/length • Sterols

  15. Sterols Moderate extremes

  16. Membrane Proteins

  17. Three types

  18. Functions of membrane proteins

  19. Properties of membrane proteins • Asymmetric • Evidence--structures • Diffuse laterally, rotate • NO flip-flop • Can be anchored to other things • Restricted mobility • Often glycosylated

  20. Evidence for Protein Mobility

  21. Glycoproteins

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