Fluid Mosaic Model

The Fluid mosaic model theory was proposed by Nicolson and Singer. The Fluid Mosaic model depicts the structure of an animal cell’s plasma membrane as a mosaic of phospholipids, cholesterol, and carbohydrates. The membranes take on a fluid quality as a result of these components. 

Every phospholipid would have a head that is hydrophilic and outside the bilayer and a hydrophobic tail that molecules with a hydrophilic head and a hydrophobic tail, phospholipids are amphipathic molecules with hydrophilic head and hydrophobic forms the interior. Cholesterol and proteins are embedded in the bilayer, giving it a mosaic appearance. Each component is responsible for a specific task

What is the Fluid Mosaic Model ?

The Fluid mosaic model was proposed by S.J. Singer and Garth L. Nicolson which demonstrates the structure of a cell membrane in which the flexible lipid layer is being spread with large protein molecules. According to the mosaic model, the components of a membrane such as the proteins in the fluid like environment to form a mobile mosaic created by the sea of phospholipids.

Structure of Fluid Mosaic Model

The Fluid Mosaic model of the cell membrane consists of a quasi fluid structure in which the proteins and the lipids are arranged in a mosaic manner. Globular proteins consist of two types which are – extrinsic proteins and intrinsic proteins. The phospholipids are the complex lipids which are made up of glycerol, two fatty acids and phosphate group which are bounded to other organic groups. Lipids (cholesterol and phospholipids) , carbohydrates are attached to some of the lipids and some proteins which are main component of the plasma membrane. Phospholipid refers to the molecules which consist of glycerol two fatty acids and a phosphate-linked head group. Another lipids are made up of four fused carbon rings which are found along the phospholipids in the membrane.

Components of Fluid Mosaic Model

Fluid mosaic model demonstrate the structure of the plasma membrane as a mosaic of the components which includes the phospholipids, cholesterol, protein and carbohydrates which provides a plasma membrane a fluid character.

Different Components	Location
Phospholipids	Phospholipids consist of the main fabric of the plasma membrane.
Cholesterol	It is located between the phospholipids and phospholipid bilayers.
Integral Proteins	These integral proteins are embedded within the phospholipid layer.
Peripheral Proteins	These peripheral proteins are embedded outside the phospholipid layer.
Carbohydrates	Outside the membrane layers they are attached to the proteins.

Phospholipids

These would have a head which is hydrophilic in nature and a tail which would be hydrophobic, phospholipids are amphipathic molecules with a hydrophilic head and a hydrophobic tail. A covalent link connects them to a glycerol molecule.

Phospholipids would be pervasive in the cells of microscopic organisms and eukaryotes. They are particles made of a phosphate head and a lipid tail. The head is viewed as water-cherishing or hydrophilic, though the tail is hydrophobic, or repellent to water. Phospholipids are thus called amphipathic. In view of this double nature of phospholipids, many sorts organize themselves into two layers in a watery climate. This is known as a phospholipid bilayer. Phospholipid amalgamation happens principally in the endoplasmic reticulum. Different areas of biosynthesis incorporate the Golgi mechanical assembly and mitochondria. 

Cholesterol

It aids in the fluidity of the plasma membrane. It exists between the phospholipids and inhibits hydrophilic tails from compacting at low temperatures and expanding at high temperatures.

Proteins

Proteins are the monomers of amino acids. There are three types of proteins in the plasma membrane:

• Integral Proteins: These would be the proteins that would form the channels that allow big molecules and ions to pass through the membrane’s hydrophobic layer.
• Peripheral Proteins: These would be the proteins that would be embedded in a single membrane leaflet. Signals are carried from one segment of the membrane to the next by them.

Glycoproteins

Glycoproteins are responsible for membrane stabilization and intercellular communication.

The liquid mosaic model makes sense of both primary and useful parts of the cell layer. It can make sense of the presence of various sorts of porousness and retentivity of different cell membrane. Fluid Mosaic model makes explain the entry of the two electrolytes and non-electrolytes through the biomembranes. Due to the underlying characteristics of the membrane surface, the cells can show different sorts of communications including acknowledgment, connection, antigen, cell receptors, and so forth.

Factors Affecting Plasma Membrane Fluidity

Three elements influence the fluidity of the cell membrane:

Temperature

According to the temperature the phospholipid arrange themselves in cluster if the temperature is cold. Phospholipid separate when the temperature of the surrounding is hot.

Cholesterol

The cholesterol molecules are dispersed randomly along the phospholipid bilayer, holding it together and preventing it from splitting too much or compacting too tightly.

Fatty Acids

Saturated and Unsaturated Fatty Acids: The phospholipid tails are made up of fatty acids. The carbon atoms in saturated fatty acid chains have a single bond, whereas the carbon atoms in unsaturated fatty acid chains have double bonds.

By causing kinks, double bonds make it more difficult for the chain to pack firmly. The fluidity of the membrane is increased by these kinks.

Restriction to Fluidity  

Fluidity of the plasma membrane is restricted due to:

Lipid Rafts

These is the lipid spaces present in the outer leaflet of plasma membrane. Lipid rafts includes cholesterol, glycosphingolipids, and glycosylphatidylinositol.

Protein Complexes

Proteins and glycoproteins are diffused inside the plasma layer. Protein helps in transportation, cell signaling, adhesion and migration of the cell.

Key Points on Fluid Mosaic Model

Some key points of Fluid mosaic model are given below:

• The plasma membrane includes amphiphilic, and phospholipid.
• The second significant part of the plasma membrane is fundamental proteins that are incorporated totally into the layer.
• Carbohydrate are present on the outer surface of the layer, where they are bound to proteins or lipids.

FAQ’s – Fluid Mosaic Model

1. What is the mosaic fluid theory ?

Cholesterol molecules and phospholipid molecules are connected together. This maintains the integrity and cohesion of the cell membrane. Because of this it is known as Fluid Mosaic Model.

2. Who proposed fluid mosaic model theory ?

The fluid mosaic model theory was being proposed by Singer and Nicolson in 1970s.

3. What are the features of fluid mosaic model membrane?

Following are the features of fluid mosaic model membrane are:

• Integral membrane protein
• Lipid bilayer, in which lipids can move in the layer but can’t cross the cell membrane.

4. Which factor affect the fluidity of cell membrane?

Following are the factor which affect the fluidity of membrane:

• Temperature
• Length of Fatty Acid tail
• Cholesterol
• Degree of saturation

5. What is the main principle of the fluid mosaic model ?

In a cell membrane the fluid mosaic model describes the structure of the cell membrane as a flexible structure which is made up of multiple components such as phospholipids, cholesterol, protein and carbohydrates.

6. Why fluid mosaic model is called so ?

The fluid mosaic mosaic model is called due to the cell membrane which is made up of multiple parts which are working together like a mosaic which is made of numerous tiles.