Davson–Danielli model

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The Davson–Danielli model (or paucimolecular model) was a model of the plasma membrane of a cell, proposed in 1935 by Hugh Davson and James Danielli. The model describes a phospholipid bilayer that lies between two layers of globular proteins and It is trilaminar and lipoprotinious.[1] The phospholipid bilayer had already been proposed by Gorter and Grendel in 1925;[2] 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[3]).

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.[4] 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 certain assumptions and couldn't account for some 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 are amphipathic and mostly hydrophobic, and to find proteins on the outside of the cell membranes where they are in contact with water is unlikely.

The Davson–Danielli model was scientifically accepted until Singer and Nicolson advanced the fluid mosaic model in 1972.[5] 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.

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References[]

  1. ^ Danielli, J. F.; Davson, H. (1935). "A contribution to the theory of permeability of thin films". Journal of Cellular and Comparative Physiology. 5 (4): 495–508. doi:10.1002/jcp.1030050409.
  2. ^ Gorter, E.; Grendel, F. (1925). "On Bimolecular Layers of Lipoids on the Chromocytes of the Blood". The Journal of Experimental Medicine. 41 (4): 439–443. doi:10.1084/jem.41.4.439. PMC 2130960. PMID 19868999.
  3. ^ Wells, W. A. (2005). "The invention of freeze fracture EM and the determination of membrane structure". The Journal of Cell Biology. 168 (2): 524–525. doi:10.1083/jcb1682fta2. PMC 2254696.
  4. ^ Paxton, Steve; Peckham, Michelle; Knibbs, Adele (2003). "The Leeds Histology Guide". {{cite journal}}: Cite journal requires |journal= (help)
  5. ^ Singer, S. J.; Nicolson, G. L. (1972). "The fluid mosaic model of the structure of cell membranes". Science. 175 (4023): 720–731. doi:10.1126/science.175.4023.720. PMID 4333397.
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