Fluid Mosaic Model of the Cell Membrane

A cell membrane is a membrane that is found surrounding the cell. It serves various purposes. It keeps the cell turgid and holds the contents of the cell. It is made up of lipid bilayer and can intake lipid-soluble substances. It serves as a barrier that prevents unwanted and unnecessary substances from entering the cell. Also, it allows the essential nutrients to make their way into the cell and helps the cell dispose of its waste material.

The names behind the fluid mosaic model of the cell membrane

In 1972, the fluid mosaic model of the cell membrane was first proposed by Garth L. Nicolson and S. J. Singer. Their theory has accuracy and describes the cell membrane for what it is. The theory explains that the cell membrane surrounding the cells’ body is made up of phospholipids, carbohydrates, cholesterol, and proteins.

Although the thickness and size of the cells vary from type of cell to cell, the cell organelles and the contents remain more or less the same. The contents of the cell depend on the function those cells have to play inside the body. For example, we can say that the mitochondrial inner membrane has 24% lipids and 76% proteins. Similarly, myelin constitutes 76% lipids and 18% proteins.

The components of the fluid mosaic model of the cell membrane and its contents

• Carbohydrates – The carbohydrates are presently attached to the outside of the membrane layer.
• Cholesterol- Cholesterol exists between the phospholipid layers.
• Intrinsic and extrinsic proteins – The intrinsic proteins are found inside the phospholipid layer, whereas the extrinsic proteins are found outside the phospholipid layer.
• A phospholipid is present throughout the cell membrane as it is the fundamental thing required for the membrane to exist. 

The main framework of the fluid mosaic model of the cell membrane

According to the fluid mosaic model, the proteins and phospholipids are arranged in the cell membrane in a mosaic manner. They make the cell membrane strong and turgid, which helps the cell wall keep the cell’s contents safe. These molecules are found moving fluidly, making the cell membrane pliable. This characteristic of the cell membrane (the movement of the molecules) hinders it from becoming a completely impregnable wall.

The theory also stated the factors that affect the cell membrane’s state. They are –

• Temperature – The temperature governs the movement of the phospholipids. When the temperature is elevated, the phospholipids move apart. Similarly, if the temperature is low, the phospholipids come closer.
• Cholesterol – It functions to bind the phospholipids together under harsh circumstances. They are randomly distributed all over and restrict the movement of unwanted things inside the cell. The existence of cholesterol molecules supports the phospholipids and helps in the functioning of the cell properly.
• Fatty acids (Saturated and unsaturated) make the phospholipids’ tails. The saturated ones are straight and, thus, easy to pack with. Unlike them, unsaturated fats are hard to pack.

The matrix is a lipid that enables the contents to flow unhindered. This is due to the hydrophobic reactions of proteins and lipids. The non-polar regions of the phospholipids bind with the non-polar regions of the surrounding molecules. The polar area is present outside. This feature gives the structure of a lipid bilayer to the cell membrane. It helps in the being of the cell membrane, a semi-permeable barrier.

A molecule that consists of glycerol, a phosphate-linked head group, and two molecules of fatty acids is called a phospholipid.

What functions does the cell membrane perform?

• Transport of amino acids and organic molecules. Passive osmosis and diffusion of oxygen, carbon dioxide, and other molecules and ions.
• Endocytosis and exocytosis are also allowed by the cell membrane of the cell. It helps the cell in discharging the waste it produces.

Importance of the fluid mosaic model of the cell membrane –

• This model mentions that the cell membranes allow compartmentalization. It means that the cell membrane divides the inner contents of the cell from the substances outside and the other cells that exist together in a tissue.
• It helps to keep the cell safe by providing cushioning. It protects the cell from any kind of injury.
• With a selective entry of both organic and inorganic substances into the cell, the cell membrane serves as a semi-permeable barrier that only allows the essential things. It also helps in disposing of the waste material produced by the cell.
• The cell membrane has attachment points that help it to get attached to the other cells inside a tissue. It also has certain substances on its surface, which give it a unique identity and help in differentiating and identifying it.

Conclusion 

In this article, we have tried to explain the fluid, functional model of the cell membrane. This theory explains the very characteristics of the cell membrane as well as its functions. It throws light on the composition and the functionality of the cell membrane. Its selective permeability helps in the proper functioning of the body by allowing the required substances to enter the cells and the waste products to leave the cell. This model is a consistent one that has its restrictions urged by thermodynamics.