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Benjamin Franklin
Benjamin Franklin poured a small amount of oil into a pond and noted that the oil spread quickly against the surface of the pond in a thin monolayer film. This revealed the hydrophobic nature of lipids. -
Lord Rayleigh (John William Strutt)
Lord Rayleigh repeated Franklin's experiments on a smaller scale. He found that an amount of olive oil that was just enough to cover the entire surface area of a bath. He obtained 16.3 Å as the thickness of the oil monolayer. Knowing the molecular structure of lipids, he assumed that the oil spread out until the layer was one molecule thick. Through a series of calculations, Rayleigh determined the thickness. Later on, his calculation would prove to be an accurate thickness of a lipid monolayer. -
Agnes Pockels
Agnes Pockels sought out Lord Rayleigh and sent him her research. Together, they published various articles on experiments she had done in her home. Her first article discussed surface tension of water. Through an apparatus of her own making, involving a tin box, would later be modified by Langmuir, she experimented with surface tension of both pure water and 'contaminated' water ( water with an oil film on top). Her experiments also measured the exact area of a lipid monolayer, as Rayleigh’s. -
Charles Ernest Overton
Overton proposed the osmotic property of the cell membrane. He hypothesized that all cells had a “lipid-impregnated boundary layer” that allowed for some molecules to pass through the membrane by dissolving into the lipid layer, which would later be called diffusion. -
Irving Langmuir
Langmuir improved Pockels' tin trough and is now referred to as Langmuir's trough. He used the trough to further learn about the relationship of water and oil as well as accurately determine the surface area covered by quantities of oil. After conducting his experiment, Langmuir proposed that the fatty acids formed a monolayer where the molecules were vertical with the carboxyl group touching the water and the hydrocarbon chains away from the water. -
Ernest Gorter and F. Grendel
Gorter and Grendel extracted lipids from red blood cells. Knowing that red blood cells have no nuclei or organelles, they assumed the lipids were from the cell membrane. They compared this to the total surface area of the red blood cell membrane measured and obtained a ratio of two. Through this experiment, they concluded that the cell membrane may consist of a phospholipid bilayer. Using this, they determined that the polar heads faced aqueous environments for both molecular layers. -
George E. Palade
George E. Palade: 1930 - George Palade perfected the process of what is now called cell fractionation. Palade ground cells together to break the membranes and have their organelles spill out. By using a centrifuge to separate organelles by mass, Palade examined organelles individually. Through this process, he further discovered functions and structures of different organelles, adding crucial information to what was later known as the endomembrane system. -
James Danielli, Hugh Davson, and E. Newton Harvey
Davson and Danielli proposed that the bi-lipid membrane was sandwiched by two layers of proteins, calling it a “lipo-protein sandwich”. Although biologists agreed that proteins were a part of the membrane, the model was incorrect since solutes would need to diffuse through the membrane which would not be possible with two layers of protein blocking the way. Additionally, their model suggested that all membranes were of a uniform thickness, which was later refuted. -
J. David Robertson
Robertson studied the cell membranes from electron micrographs of sectioned material and concluded that the plasma membrane and the membranes of all cell organelles were similar in structure. He proposed a variation of the model where the bi-layers were surrounded by a thin layer of proteins and carbohydrates. Robertson called it the 'unit membrane' and hypothesized that all membranes in the cell are of this model. -
Jonathan Singer and Garth Nicolson
Singer and Nicolson introduced the fluid mosaic model in 1972. According to this model, the cell membranes are visualized as mosaics of lipids and proteins. The model still has the lipid bilayer structure as proposed by Grendel and Gorter. However, in this model, the lipids are thought to be arranged in a bilayer in which proteins are scattered throughout. These proteins are suggested to contain channels and that the entire model is fluid, meaning that all molecules are freely moving.