Question

Short / Long answer type questions.
Describe the fluid-mosaic model of membrane structure as well as the models that preceded it. Cite the evidence that either disproves or supports these models.

Answer 1

• The recently accepted model for the plasma membrane is the Fluid mosaic model which was given by Singer and Nicholson.
• As per this model the membrane are formed by a continous bilayer of lipids into which protein complexes are embedded in kind of a "mosaic" arrangement.
• There are other proteins present peripheral to the bilayer or are disposed on the inner surface.
• The molecular asymmetry is further emphasized by the oligosacherides chains of the glycoproteins and the glycolipids that protrude only at the outer surface.
• In plasma membrane of the human red cell the membrane is made up of 52% protein, 40% lipid.
• Before the idea of the fluid mosaic model the models that preceeded it were as folllows.
• Lipid monolayer given by Lagmuir(1905) as per which the lipid layer with polar and non polar ends present only in a single layer.
• Lipid bilayer sheet given by Gorter and Grendel(1926) as per which lipid are arranged in a bilayer as a sheet with the present of proteins or orther components.
• Lipid bilayer plus protein sheets given by Davson and Danielli(1935) where lipid bilayer is coated with thin sheets of proteins on both sides.
• Unit membrane model given by Robertson(1960) where all the cellular membrane share a common underlying structure where 2 layers of lipid are sandwiched between two sheets of proteins
• After which fluid mosiac model was given in 1972 by Singer and Nicholson
• All the model that were given by the time before fluid mosaic model were not able to solve the question as to why some of the molecules are not able to pass through the layer while some are able to pass through it.
  
• Therefore fluid mosaic model of cell membrane is the widely accepted model compared to the other models provided before it.