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History of Cell Membrane Models
Transcript of History of Cell Membrane Models
Pliny The Elder
Charles Ernest Overton
Gorter and Grendel
Danielli, Daveson, and Harvey
Singer and Nicolson
Unwin and Henderson
One of the first to write about the effects oil has on water when the two are mixed together, Pliny the Elder recorded his findings in his encyclopedic work, Natural History. He wrote that “...seawater is made smooth by oil, and so divers sprinkle oil on their face because it calms the rough element…”
Did experiments with oil to determine its effects when poured on water. Franklin poured a small amount of oil on a lake in Clapham Common and quickly noticed that the oil spread over the pond until a large section was covered, creating a surface that was “smooth as a looking glass”.
Conducted the same experiment as Benjamin Franklin and was able to determine the area of water that a known volume of oil would cover and the thickness of the layer of oil. He published his results and was then contacted by Agnes Pockles.
Conducted experiments involving oil and water in her own kitchen before writing to Lord Rayleigh who later joined her to help her publish her works. However, she is most known for developing the langmuir apparatus, a device used to determine the exact area of a surface covered by an oil film, which is still used today.
Came up with the theory that the membrane is composed of lipids. He discovered this on accident while working with plants in an experiment where he to determine substances able to diffuse in plant cells. This also led to the discovery that non-polar substances pass quickly through the membrane, which contrasted previous knowledge.
Made artificial membranes by dissolving phospholipids with benzene. Observed that even after the benzene dissolved the phospholipid layer remained as a film on the water. Came up with the model that the lipid layer forms a monolayer with the polar heads in contact with the water and their hydrocarbon tails away from the water. Also remade Agnes Pockles's device.
These two were the first to study the lipids from the cell itself using red blood cells. Using chemical solvents, they extracted the phospholipid part of the membrane from these cells. They discovered that it could cover the cell twice around because the surface area was double that of the cell. They repeated the experiment with several different animals and ultimately concluded that red blood cells have a double phospholipid bilayer. This was not a model for all cells but was a plausible structure for the membrane.
They created the first cell membrane model which was a "sandwich" of lipids in between two layers of proteins. They found that oil droplets could be absorbed by mackerel eggs which shows how the proteins are in place and stable since the are absorbed by the phospholipid layer.
Developed the fluid mosaic model which keeps the same lipid bilayer structure of the unite membrane model but the proteins float within the lipid bilayer instead of sandwiching the lipids. The hydrophobic tails on the phospholipids are on the inside, facing away from the water. The hydrophilic heads are on the outside, pointed toward the water. Inside of this bilayer are the proteins. The intire membrane is fluid and the proteins float freely.
These two discovered that the parts of the proteins spanning the lipid bilayer are hydrophobic in nature and are arranged in a shape often in the form of an alpha helix.