The Davson–Danielli model (or paucimolecular model) was a model of the plasma membrane of a cell, proposed in 1935 by

Hugh Davson Hugh Davson, Baron Davson (25 November 1909 – 2 July 1996) was an English physiologist who worked on membrane transport and ocular fluids. Davson was born in Paddington, London, the son of physician Wilfred Maynard Davson and Mary Louisa Scott. ...

and

James Danielli James Frederic Danielli FRS (1911–1984) was an English biologist. He was famous for research on the structure and the permeability of cell membranes The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and ...

. The model describes a

phospholipid bilayer The lipid bilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around all cells. The cell membranes of almost all organisms and many vir ...

that lies between two layers of

globular protein In biochemistry, globular proteins or spheroproteins are spherical ("globe-like") proteins and are one of the common protein types (the others being fibrous, disordered and membrane proteins). Globular proteins are somewhat water-soluble (formi ...

s, which is both trilaminar and lipoprotinious. The phospholipid bilayer had already been proposed by Gorter and Grendel in 1925; however, the flanking proteinaceous layers in the Davson–Danielli model were novel and intended to explain Danielli's observations on the surface tension of lipid bilayers (It is now known that the phospholipid head groups are sufficient to explain the measured surface tension). Evidence for the model included electron microscopy, in which high-resolution micrographs showed three distinct layers within a cell membrane, with an inner white core and two flanking dark layers. Since proteins usually appear dark and phospholipids white, the micrographs were interpreted as a phospholipid bilayer sandwiched between two protein layers. The model proposed an explanation for why certain substances were not able to pass through cell membranes, while also accounting for the thinness of membranes. Despite the Davson–Danielli model being scientifically accepted, the model made assumptions, and couldn't account for observed phenomena. For example, the model assumed that all membranes had the same structure, which couldn't explain how different types of membranes could have different functions. Another shortcoming of the Davson–Danielli model is that proteins, while

amphipathic An amphiphile (from the Greek αμφις amphis, both, and φιλíα philia, love, friendship), or amphipath, is a chemical compound possessing both hydrophilic (''water-loving'', polar) and lipophilic (''fat-loving'') properties. Such a compoun ...

, are mostly hydrophobic, so the existence of proteins on the outside of the cell membranes in direct contact with water presented an issue. The Davson–Danielli model was scientifically accepted until Seymour Jonathan Singer and Garth L. Nicolson advanced the

fluid mosaic model The fluid mosaic model explains various observations regarding the structure of functional cell membranes. According to this biological model, there is a lipid bilayer (two molecules thick layer consisting primarily of amphipathic phospholipids ...

in 1972. The fluid mosaic model expanded on the Davson–Danielli model by including transmembrane proteins, and eliminated the previously-proposed flanking protein layers that were not well-supported by experimental evidence. The experimental evidence that falsified the Davson–Danielli model included membrane freeze-fracturing, which revealed irregular rough surfaces in the membrane and fluorescent antibody tagging of membrane proteins, which demonstrated their fluidity within the membrane.

References

{{DEFAULTSORT:DavsonDanielli model Cell anatomy

See also

References