260 likes | 443 Views
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
E N D
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 Lipid bilayer was not enough to describe differential permeability • Hugh Davson and James Danielli—1935 • Protein-lipid "sandwich"
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 • 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 • 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 • Phospholipids • Glycolipids • Sterols
Different membranes, different lipids Differ between layers of the bilayer--assymetric
Maintaining Fluidity • Fatty acid type/length • Sterols
Sterols Moderate extremes
Properties of membrane proteins • Asymmetric • Evidence--structures • Diffuse laterally, rotate • NO flip-flop • Can be anchored to other things • Restricted mobility • Often glycosylated