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Fluid Mosaic Model – Definition, Types, Factors Affecting, Examples

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  • Last Updated : 23 Jun, 2022

Nicolson proposed the fluid mosaic model. This 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 in nature and outside the bilayer and a hydrophobic tail that molecules with a hydrophilic head and a hydrophobic tail, phospholipids are amphipathic molecules with a 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

Phospholipids

These would have the head which is  hydrophilic in nature and the 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. 

Different types of lipids 

Inside these two significant classes of lipids, there are various explicit sorts of lipids, which are critical to life, including unsaturated fats, fatty oils, glycerophospholipids, sphingolipids and steroids. These are extensively delegated basic lipids and complex lipids.

Basic Lipids-Esters of unsaturated fats with different alcohols.

  • Fats: Esters of unsaturated fats with glycerol. Oils are fats in the fluid state
  • Waxes: Esters of unsaturated fats with higher subatomic weight monohydric alcohols
  • Complex Lipids-Esters of unsaturated fats containing bunches notwithstanding liquor and unsaturated fat.

Phospholipids: These are lipids containing, notwithstanding unsaturated fats and liquor, phosphate bunch. They much of the time have nitrogen-containing bases and other substituent, e.g., in glycerophospholipids the liquor is glycerol and in sphingophospholipids the liquor is sphingosine. Glycolipids (glycosphingolipids): Lipids containing an unsaturated fat, sphingosine and starch. Other complex lipids: Lipids, for example, sulfolipids and amino lipids. Lipoproteins may likewise be put in this class.

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 

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

  • Integral Proteins

These would be the  proteins which would form the channels  that allow big molecules and ions to pass through the membrane’s hydrophobic layer.

  • Peripheral Proteins
Cell Membrane

 

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 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 films. The model makes sense of the entry of the two electrolytes and non-electrolytes through the biomembranes. Due to the underlying characteristics of the film surface, the cells can show different sorts of communications including acknowledgment, connection, antigen, data receptors, and so forth.

Factors Affecting Plasma Membrane Fluidity

Three elements influence the fluidity of the cell membrane:

  • Temperature- When it’s cold, phospholipids cluster together. When it’s hot outside, they separate.
  • 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- 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.

The liquid property of practical natural films not entirely settled through naming analyses, x-beam diffraction, and calorimetry. These examinations showed that basic layer proteins diffuse at rates impacted by the consistency of the lipid bilayer in which they were implanted, and exhibited that the particles inside the cell film are dynamic as opposed to static.

Past models of organic films incorporated the Robertson Unit Membrane Model and the Davson-Danielli Tri-Layer model. These models had proteins present as sheets adjoining a lipid layer, as opposed to integrated into the phospholipid bilayer. Different models portrayed rehashing, standard units of protein and lipid. These models were not all around upheld by microscopy and thermodynamic information, and didn’t oblige proof for dynamic film properties.
The liquid mosaic model makes sense of changes in design and conduct of cell films under various temperatures, as well as the relationship of layer proteins with the films. While Singer and Nicolson had significant proof attracted from various subfields to help their model, late advances in fluorescence microscopy and primary science have approved the liquid mosaic nature of cell films.
Be that as it may, the proteins at last diffused, and over the long haul the line between the two parts was lost. Bringing down the temperature eased back the pace of this dispersion by making the film phospholipids change from a liquid to a gel stage. Artist and Nicolson justified the consequences of these investigations utilizing their liquid mosaic model.

Temperature affecting fluidity of membrane and its mechanism 

High Temperature Increases Fluidity

Cells work best at typical physiological temperature, which is 98.6 degrees Fahrenheit in warm-blooded creatures like people. On the off chance that internal heat level increments, for instance during a high fever, the phone layer can turn out to be more liquid. This happens when the unsaturated fat tails of the phospholipids become less unbending and permit greater development of proteins and different atoms in and through the layer. This can change the porousness of the cell, perhaps permitting a few possibly hurtful particles to enter. Both basic and fringe proteins in the film can likewise be harmed by high temperatures and, assuming that very high, intensity could make these proteins separate, or denature.

Low Temperature Stiffens the Membrane

A decline in temperature can likewise adversely affect cell layers and cells. At low temperature, the unsaturated fat tails of the phospholipids move less and become more inflexible. This diminishes the general ease of the layer, additionally diminishing its porousness and possibly limiting passage of significant particles like oxygen and glucose into the cell. Low temperature can likewise sluggish cell development by forestall the cell’s expansion in size. In outrageous circumstances, for example, delayed openness to sub-frigid temperatures, fluid in the cell can start to freeze, shaping precious stones that puncture the layer and could eventually kill the cell.

Key points 

  • The plasma film includes amphiphilic, phospholipid atoms.
  • The second significant part of the plasma film is fundamental proteins that are incorporated totally into the layer.
  • Sugars are found on the outer surface of the layer, where they are bound to proteins or lipids.

Restriction to fluidity  

Lipid Rafts-These are the lipid spaces tracked down on the outside pamphlet of the plasma layer. Cholesterol, glycosphingolipids, and glycosylphosphatidylinositol are the structure blocks of lipid pontoons.

Protein Complexes – Proteins and glycoproteins are diffused inside the plasma layer. This assistance in the vehicle of particles and metabolites, cell flagging, bond, and movement

Conceptual Questions 

Question 1: What is the meaning of the term “fluid mosaic model”?

Answer:

Cholesterol molecules and phospholipid molecules are connected together. This maintains the integrity and cohesion of the cell membrane. 

Question 2: Cholesterol would help in?

Answer:

Cholesterol helps in maintaining the fluidity of the cell membrane.

Question 3: What happens when the temperature fluctuates?

Answer:

According to the temperature, if the temperature increases the fluidity so to maintain that phospholipids change their structure and vice versa to maintain the fluidity of the cell membrane.

Question 4: Cell membranes are made from?

Answer: 

They are made from phospholipids and proteins. The phospholipids are amphipathic in nature i.e., both hydrophobic and hydrophilic in nature

Question 5: What types of proteins are present incell membrane?

Answer:

Glyco, integral, and peripheral proteins are the different types of proteins.


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