Question

Difference between unit membrane model and fluid mosaic model

Answer 1

(I) Lipid Bilayer Hypothesis:

Overton (1895) suggested that the cell membranes contain lipids. This conclusion was based on the fact that fat solvents dissolved the membrane easily and fat soluble substances passed easily through the cell membranes. Some workers like Hober (1910) and Fricke (1925) found low electrical conductivity in the cell membrane which indicated the presence of lipid layer

(i) Danielli and Davson Model:

Harvey and Coley (1931) and Danielli and Harvey (1935) studied surface tension of cell membrane and on the basis of their observation they pointed out the existence of protein molecules adsorbed on the surface of lipid droplets which reduce the surface tension of droplets.

This conclusion led James Danielli and Hugh Davson in 1935 to suggest bimolecular leaflet model of cell membrane. Danielli and Davson model was the first attempt to describe membrane structure in terms of molecules and to relate the structure to biological and chemical properties.

According to bimolecular model of Danielli and Davson, plasma membrane consists of two layers of phospholipid molecules (a bimolecular leaflet) in which phospholipid molecules are arranged in such a way that hydrophilic heads of the phospholipid molecules face outside and hydrophobic non-polar lipid chains are associated in the inner region of leaflet.

The hypothesis also suggested that the polar ends of lipid molecules are associated with monomolecular layer of globular proteins. The plasma membrane would thus consist of a double layer of phospholipid molecules sandwiched between two essentially continuous layers of protein (Fig. 2.2).



(ii) Unit Membrane Model:

In 1950 J. David Robertson studied the cell membranes from electron micrographs of sectioned material. The preparations involved usual fixing in solutions of osmium tetraoxide and potassium permanganate (KMnO4), and dehydrating in solvents such as acetone before sectioning.

In late 1950s Robertson summarised a large number of ultra-structural data obtained by him and some other workers and concluded that the plasma membrane and the membranes of all cell organalles were similar in structure. Although the similarity is not resolved by light microscopy, it is clearly seen in electron micrographs.

Answer 2

Unit Membrane Model  and Fluid Mosaic Model  

Explanation:

Role of unit Membrane model  

• A cell layer,the materials enter or leave the cell. Dispersed in the lipid bilayer are cholesterol particles, which help to keep the membrane  liquid predictable
• Membrane proteins are significant for shipping substances over the cell layer.They can likewise work as enzymes or receptors  

Role of Fluid Mosaic model  

• The liquid mosaic model depicts the cell membrane as a tapestry of a few kinds of atoms (phospholipids, cholesterols, and proteins) that are continually moving
• This development enables the cell membrane to keep up its role as an obstruction between within and outside of the cell environments