Fluid mosaic model is similar to Robertson model in

The fluid mosaic model was proposed by S.J. Singer and Garth L. Nicolson. This model explains the structure of the plasma membrane of animal cells as a mosaic of components such as phospholipids, proteins, cholesterol, and carbohydrates. These components give a fluid character to the membranes.

Each phospholipid has a hydrophilic head pointing outside and a hydrophobic tail forming the inside of the bilayer.

Cholesterol and proteins are embedded in the bilayer that gives the membrane a mosaic look. Each component has a specific function to perform.

Table of Contents

Also Read: Cell membrane and plasma membrane

Components of Plasma Membrane

ComponentsLocationPhospholipidThe main fabric of plasma membraneCholesterolBetween phospholipids and phospholipid bilayersIntegral proteinsEmbedded within phospholipid layersPeripheral proteinsInner or outer surface of the phospholipid bilayerCarbohydratesAttached to proteins on outside membrane layers

Phospholipids

Phospholipids are amphipathic molecules with a hydrophilic head and a hydrophobic tail. These are attached to a glycerol molecule by a covalent bond.

Cholesterol

It helps the plasma membrane to retain the fluidity. It is present between the phospholipids and prevents the compaction of hydrophilic tails at low temperatures and their expansion at high temperatures.

Proteins

The plasma membrane has three types of proteins:

Integral Proteins: These proteins form channels to allow the movement of large molecules and ions across the hydrophobic layer of the membrane.
Peripheral Proteins: These are found embedded in a single leaflet of the membrane. They carry signals from one segment of the membrane and relay it to the another.
Glycoproteins: They stabilize the membrane and are responsible for intercellular communication.

Factors Affecting Fluidity of Plasma Membrane

The fluidity of the cell membrane is influenced by three factors:

Temperature

Phospholipids are found close together when it is cold. When it’s hot, they move apart.

Cholesterol

The cholesterol molecules are randomly distributed along the phospholipid bilayer and hold it preventing it from separating too far, or compact too tightly.

Saturated and Unsaturated Fatty Acids

Fatty acids make up the phospholipid tails. Saturated fatty acid chains have a single bond between the carbon atoms whereas, unsaturated fatty acid chains have double bonds between the carbon atoms.

Double bonds make it harder for the chain to pack tightly by creating kinks. These kinks increase the fluidity of the membrane.

Restriction to Fluidity of Plasma Membrane

The fluidity of plasma membrane is restricted due to:

Lipid Rafts

These are the lipid domains found on the external leaflet of the plasma membrane. Cholesterol, glycosphingolipids, glycosylphosphatidylinositol are the building blocks of lipid rafts.

Protein Complexes

Proteins and glycoproteins are diffused within the plasma membrane. These help in the transport of ions and metabolites, cell signalling, adhesion, and migration.

Key Points on Fluid Mosaic Model

The plasma membrane comprises amphiphilic, phospholipid molecules.
The second important component of the plasma membrane is integral proteins that are integrated completely into the membrane.
Carbohydrates are found on the external surface of the membrane where they are bound to proteins or lipids.

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Frequently Asked Questions

Why is it called fluid mosaic model?

The phospholipid molecules and the molecules of cholesterol are linked together. This keeps the cell membrane intact and cohesive. This is why it is called fluid mosaic model.

What are the features of the membranes of fluid mosaic model?

The membranes of fluid mosaic model include:

A lipid bilayer, where lipids are free to move but cannot cross the membrane.
Integral membrane proteins

What causes the fluidity of plasma membrane?

The elasticity and fluidity of plasma membrane are due to lipid molecules. The membrane proteins give semi-permeability to the plasma membrane.

Which factors affect the fluidity of the plasma membrane?

The fluidity of the plasma membrane is affected due to:

Length of the fatty acid tail
Temperature
Cholesterol
Degree of saturation of fatty acid tails

What are integral and peripheral proteins?

Peripheral proteins are those that are located in the inner and outer layer of phospholipid bilayer, whereas, integral proteins are embedded within the bilayer.

What is another name for the fluid mosaic model?

The cell membrane, whose structure is described in the fluid mosaic model, is also called the plasma membrane or the plasmalemma.

What is difference between davson Danielli model and fluid mosaic model?

The Davson–Danielli model predominated until Singer and Nicolson advanced the fluid mosaic model in 1972. 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.

What was the fluid mosaic model based on?

The fluid mosaic model describes the structure of the plasma membrane as a mosaic of components —including phospholipids, cholesterol, proteins, and carbohydrates—that gives the membrane a fluid character.

How is fluid mosaic model different from other models?

The key difference between fluid mosaic model and sandwich model is that fluid mosaic model states that cell membrane is a fluid phospholipid bilayer in which proteins are either partially or wholly embedded while sandwich model described the cell membrane structure as a lipid layer sandwiched between two protein ...