How did we find out the plasma membrane is a bilayer?

During the late 1800's not much was known about the boundary surrounding cells, except that there was one, and it was probably made of lipids (Overton, 1889). In 1924, Gorter and Grendel wanted to know how lipids surrounding cells were organized. Using red blood cells from mammals (which lack membrane bound organelles) and estimated their surface area. They extracted the lipids from these cells and spread them out into a layer 1 molecule thick. Measuring the area of this monolayer and found it to be almost exactly 2 times greater than the surface area of the cells the lipids had been come from. Their conclusion: if cells are covered in lipids, and there are enough lipids to cover the surface of a cell twice, then cells are actually covered by lipids two molecules thick (a bilayer).

• The paper

Something extra. A short and interesting primer on the discovery of the lipid bilayer from Nature Education.

Gorter and Grendel used a modified version of a Langmuir Trough to measure the surface area of lipids extracted from mammalian red blood cells.

Source: Nature Education