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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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a bit of history
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
slide4
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"
slide5
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
problems with this theory
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
fluid mosaic model
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)
the lipids of membranes
The Lipids of Membranes
  • Phospholipids
  • Glycolipids
  • Sterols
different membranes different lipids
Different membranes, different lipids

Differ between layers of the bilayer--assymetric

maintaining fluidity
Maintaining Fluidity
  • Fatty acid type/length
  • Sterols
slide20

Sterols

Moderate extremes

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