Is Endocytosis Phagocytosis:Similarities & Differences


In this article, we will have a comparative analysis with detailed facts and explanations on “Is Endocytosis Phagocytosis: Similarities & Differences”.

Endocytosis is the cellular process in which the cell membrane invaginates to internalize macromolecules and then buds off to form a vesicle containing that material. Thus it is a process of engulfing performed by the cells and is mostly involved in the various functions.

Phagocytosis is a process of endocytosis where a particular cell identifies and engulfs other cells and pathogens.

Here is a comparison of the two processes.

CharacteristicsEndocytosisPhagocytosis
ProcessThe cell membrane surrounds the particle to be engulfed and traps it into a separate fluid containing a vesicle-like structure, internalized by the whole cell.The cell identifies and engulfs large size particles especially cell debris, and microorganisms into a separate vesicle-like structure called Phagosomes.
TypesEndocytosis is mostly of three types :
·         Receptor-mediated
·         Pinocytosis
·         PhagocytosisPhagocytosis is a type of endocytosis and is differentiated based on the cells that perform it.
Examples of cells that perform the process·         Clathrin-coated cells that fuse with endosomes
·         Lysosomes
·         Cells of the Immune system
·         Cells involved in the transport
. Cells involved in nutrient supply
Phagocytic cells of the immune system for example :
·         Neutrophils
·         Macrophage
·         Monocytes
·         Dendritic cells
Examples of materials engulfed·         Protein-ligands with specific receptors for transport
·         Extracellular fluid with ions, sugar, and nutrients
·         Bacterial cells, pathogens, cell debris
. Cholesterol, lipoproteins, transferrin.
Large particles >0.5 micrometer
mainly foreign bodies like bacterial cells, cell debris, and pathogens with a specific shape and expressing particular receptors.
FunctionTransport of large molecules that cannot undergo diffusion, Immunity, and nutrition.It is a mechanism of innate immunity in response to pathogens and bactetia and nutrition in protists.
Difference of Endocytosis and Phagocytosis

Endocytosis

The main steps in the process of Endocytosis are :

Invagination – When a particle needed to be endocytosed comes in the vicinity of the plasma membrane, it folds inward to form a cavity around the particle.

Vesicle-formation- The invaginated membrane then surrounds the particle and folds back to itself in a way of enclosing the cavity around the particle. Thus a vesicle is formed trapping the particle.

Detachment- The vesicle consisting of the particle along detaches from the cell membrane which is internalized in the cell for further processing.

is endocytosis phagocytosis
Basic steps of Endocytosis from Wikimedia

Types of Endocytosis

There are three main types of Endocytosis processes performed by the cells. They are:

Receptor-mediated Endocytosis

Pinocytosis

Phagocytosis

Receptor-mediated Endocytosis

It is also called Clathrin-mediated endocytosis. This type of endocytosis is mainly used for recycling signaling receptors and transporting macromolecules inside the cell.

Mechanism: 

1. Phosphatidylinositol-4,5-bisphosphate (PIP2) accumulates in the cell membrane by the action of phosphoinositide. The PIP2 associates with adapter proteins to initiate the attachment of protein Clathrin in the plasma membrane that ultimately forms Clathrin-coated vesicles.

2. Clathrin-coated pits are formed in the membrane by the action of adaptor proteins that incorporate clathrin in the membrane lipids forming a concave shape.

3. When a receptor-associated ligand needs to be endocytosed, they form a cluster on the clathrin-coated pits.

4. Dynamin protein helps the pits to invaginate and form clathrin-coated vesicles that ultimately cut off from the membrane. The adaptor proteins and clathrin are then released from the vesicles that fuse with endosomes.

5. Endosomes help to recycle and sort the ligands and release macromolecules inside the cells.

Some Examples of Clathrin-mediated endocytosis are recycling of Transferrin protein and uptake of Cholesterol.

Receptor-mediated Endocytosis from Wikipedia

Pinocytosis

It is also called cell drinking because here fluid and dissolved small molecules undergo endocytosis for nutrient uptake and digestion by lysozyme.

Mechanism:

1.The cell membrane invaginates and engulfs extracellular fluid along with minute particles dissolved in it and forms a vesicle.

2.The vesicle fuses inside the cell with endosomes containing lysozyme.

3.The Lysozyme degrades the particles and dissolves the membrane of the vesicle to release the fluid inside the cell.

4.When particles of size 0.1 µm are transported it is called Micropinocytosis and when the size of particles ranges from 0.5-5 µm it is called Macropinocytosis.

An example of Pinocytosis is the uptake of nutrients in the small intestine.

Phagocytosis

It is a mechanism of cell-eating and part of immune response in higher organisms and also a system of nutrient supply for protozoans like the amoeba. Mostly large particles and living cells undergo phagocytosis.

Mechanism

1.The cells that perform phagocytosis are called phagocytic cells and have particular receptors to sense the foreign bodies needed to be endocytosed.

2.The cells attach themselves to the foreign particle like bacterial cells and extend their membranes to surround the particle.

3.Then the cells engulf the bodies into a vesicle called phagosomes

4.Phagosomes fuse with endosomes containing lytic enzymes called Lysozymes.

5.The lysozymes degrade the foreign bodies and they are released out of the cells.

6.The receptors and chemical attachment of the phagocytes with the pathogens vary depending on the nature of the pathogens and cells.

An example of Phagocytosis is cells like macrophages , Monocytes, Dendritic cells that target specific pathogens and engulf and degrade them.

Process of Phagocytosis from Wikipedia

Conclusion

Endocytosis and Phagocytosis both are cellular processes of internalizing particular materials. The mechanism of both the processes are similar and Phagocytosis is classified as a type of Endocytosis. The difference between the two processes is that the function of Phagocytosis is to destroy foreign bodies or supply nutrition to the cells. Also, there are specific cells to perform the task of phagocytosis and definite signals to direct the process which differ from the other two methods of Endocytosis.

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