Plasma membrane

*Plasma membrane is also called Bio-membrane/Cell membrane.

Properties of Plasma membrane-:

 - Madeup of (Protein+ Phospholipid). 

 - it is selectively permable membrane.

 - it is a Dynamic membrane.

Type of Plasma Membrane-:

These are mainly three type 

 1)Sandwich Model

 2)Unit Membrane Model

 3)Fluid Mosaic Model 

1)Sandwich Model-:

   - given by "Danielli & Davson" 

  Ques-Why this is called sandwich model?

 Ans a) Plasma membrane are Madeup of Protein & Phospholipid.

       b) Protein are Madeup of alpha-globular structure. 

       c) Phospholipid are amphipathic in nature. Amphipathic means--each Phospholipid are two end - 1)Head end which is madeup of glycerol and Hydrophilic(loving with water) in nature. 

  2)Tail end which is madeup of Fatty acid chain and Hydrophobic(hate with water) in nature.

       d) Phospholipid layer are arranged in bylayer manner such as tail are face each other & protein on either side of Phospholipid layer.

 

Sandwich Model of PlasmaMembrane 

Drawback of Sandwich Model-:

 1) fat soluble substance move inside membrane. 

2) Water soluble substance can not cross in this model. 

3) This model also not explain dynamic nature of Plasma membrane. 

2) Unit Membrane Model-:

  This model given BY-J.Devid Robertson. 

Properties-:

a) (according to Robertson this model are Beta-fiberus protein) these are thread like structure. 

b) Plasma membrane is protein & Phospholipid layer.they are arranged in as like Sandwich model. 

c) thickness of Plasma membrane (75-100 Angstrom) 

  

3) Fluid-Mosaic Model-: 

 Discovered by-"S.J.Singer & G.L.Nicholson"

In this model all information are same as Danielle & Davson but interpretation are totally different - 

   Properties-:

   a) Plasma membrane is madeup of Protein & Phospholipid. 

   b) Protein are alpha-gloubler protein. 

      according to Singer & Nicholson this protein are classified in two type-

 1) Extrinsic Protein-:

  *It present outside the membrane       attached to Phospholipid layer. 

*loosely attached. 

 2) Intrinsic Protein-:   

   *Present on partial or completely inside Phospholipid bilayer. 

  *compact attached. 

  

Phospholipid bilayer are show two type movement-

  1)Transition movement- Movement of Phospholipid molecules in same layer. 

 2) Flip-flop movement- Movement of Phospholipid molecules between two layer. 

       Protein---Phospholipid --- Protein  

                               OR

                     Trilammilar model 

NOTE- This model show dynamic nature of Plasma membrane. 

- Water move inside the membrane by the help of Intrinsic Protein/Channel Protein. 

-fat soluble substance move inside the membrane. 

So, that is most acceptable model nowadays. 

       Structure of Fluid-Mosaic Model 

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