About seven decades ago, Gorter and Grendel, the "founding fathers" of our current model of plasma membrane structure, predicted quite simply that if a plasma membrane were really a bilayer then its surface area should be half that occupied by all its amphipathic lipids spread out in a monolayer. To test this prediction, they measured the surface areas of different mammalian erythrocytes microscopically. Independently, they also extracted the lipids from erythrocyte membranes (from the samples used for measurements of cell surface areas), spread the lipids out at an air/saline interface and measured the respective monolayer surface areas. Comparison of these two measurements produced a cell:monolayer surface area ratio of approximately 1:2 for a number of different mammalian red cells, thereby confirming their bilayer model of the plasma membrane.
Why weren't their ratio measurements exactly 1:2? Also, as we've already seen (opposite page), bilayers vary in their degree of lateral compaction; monolayers do as well. How could Gorter and Grendel standardize this feature in their experiment? Is a 2:1 ratio reasonable? Do their measurements and their model ignore crucial features of plasma membranes? Are there other ways of testing the bilayer hypothesis?
Where's all the membrane protein? Continue on to the [Section 5 - under construction] to examine this question and to explore the nature of integral and peripheral proteins. [If you've been following this thread from a LabBook presentation of Membrane Fluidity, you can easily return to this topic.]