Difference Between Endocytosis and Transcytosis

The key difference between endocytosis and transcytosis is that endocytosis is a cellular mechanism by which cells uptake materials inside the cell by invagination of the cell membrane and forming a vesicle surrounding the materials, while transcytosis is a cellular mechanism that transports various macromolecules across the interior of a cell.

Cells take things in and eject certain things from the cell. Endocytosis and transcytosis are two types of cellular transport mechanisms. Endocytosis facilitates the uptake of materials into the interior of the cell via internalization and vesicle formation. Transcytosis facilitates transcellular transport of various macromolecules across the interior of a cell. Both endocytosis and transcytosis are important cellular mechanisms.

CONTENTS

1. Overview and Key Difference
2. What is Endocytosis
3. What is Transcytosis
4. Similarities Between Endocytosis and Transcytosis
5. Side by Side Comparison – Endocytosis vs Transcytosis in Tabular Form
6. Summary

What is Endocytosis?

Endocytosis is a cellular mechanism that helps to take in substances into the interior of the cell. When the necessary materials arrive near the plasma membrane, plasma membrane surrounds and internalizes them. Then it buds off inside the cell, forming a vesicle containing those materials. There are three forms of endocytosis: phagocytosis, pinocytosis and receptor-mediated endocytosis.

Phagocytosis is the process of taking large solid matter such as cell debris, pathogens like bacteria, dead cells, dust particles, small mineral particles, etc, into the cell by forming phagosomes. Most of the immune cells including tissue macrophages, neutrophils and monocytes are professional phagocytic cells. Generally, phagocytosis is a defence mechanism which destroys the invading pathogens by engulfing them into phagosomes and later destroying them inside the cell. A lytic action takes place inside the cell where a lysosome binds to the phagosome and releases lytic enzymes to destroy the engulfed pathogen or solid matter by forming a phagolysosome.

Pinocytosis is another form endocytosis in which extracellular fluid is taken inside the cell by forming small vesicles. Small molecules that are suspended in the extracellular fluid are transported through this mechanism. Pinocytosis does not select the molecules to transport. Whatever the small molecules present in the water are ingested by pinocytosis. Hence, it is not considered as a specific process. It is also not an efficient process. However, pinocytosis takes place in most cells. In fact, pinocytosis is the typical molecule transport mechanism in liver cells, kidney cells, capillary cells and epithelial cells.

Receptor-mediated endocytosis is the third form of endocytosis in which macromolecules are taken up by the cell selectively from the extracellular fluid. This mechanism is mediated by receptors on the cell surface and specific binding with the macromolecules outside the cell. Receptors that are involved in receptor-mediated endocytosis are concentrated in clathrin-coated pits. Receptor-mediated endocytosis is a very specific mechanism of up taking molecules into the cells, unlike pinocytosis. Materials transported inside are decided by the receptors present on the cell membrane surface. It is also an efficient process than pinocytosis.

What is Transcytosis?

Transcytosis is a type of transcellular transport of macromolecules such as enzymes, antibodies and proteins, etc. In simple words, transcytosis is a way of transporting macromolecules across the interior of a cell. It involves both endocytosis and exocytosis. From one side of the cell, macromolecules enter the cell through endocytosis then travel across the cell and reach the other side of the cell. Then through exocytosis, macromolecules exit the cell. In this way, macromolecules are captured in vesicles in one side, then they are transported across the cell and they are ejected from the cell via exocytosis finally from the other side.

Transcytosis is most commonly observed in epithelial cells, especially in secretary cells. Also, transcytosis acts as a convenient mechanism by which pathogens can invade a tissue.

What are the Similarities Between Endocytosis and Transcytosis?

• Both endocytosis and transcytosis are two cellular processes.
• Transcytosis involves endocytosis as well.
• Both mechanisms facilitate the uptake of materials inside the cell.
• These mechanisms form membrane coated vesicles.

What is the Difference Between Endocytosis and Transcytosis?

Endocytosis is a cellular process in which substances are brought into the cell. Meanwhile, transcytosis is a type of transcellular transport that transports various macromolecules across the interior of a cell. So, this is the key difference between endocytosis and transcytosis. Furthermore, endocytosis facilitates the uptake of small molecules, macromolecules, suspended molecules, pathogens, etc., while transcytosis transports various macromolecules such as enzymes, proteins and antibodies, etc. across the interior of the cell from one side to the other side of the cell and releases from the cell. Therefore, this is also a significant difference between endocytosis and transcytosis. Also, transcytosis involves exocytosis, unlike in the endocytosis.

Summary – Endocytosis vs Transcytosis

Endocytosis is a cellular process by which cell membrane captures materials in a pocket that turns into a vesicle and carry its contents to the cell’s interior while transcytosis is a transcellular process that takes in materials from one side of a cell, transports them across the cell in the form of membrane-coated vesicles and releases on the other side of the cell. Thus, this is the key difference between endocytosis and transcytosis.

Reference:

1. Cooper, Geoffrey M. “Endocytosis.” The Cell: A Molecular Approach. 2nd Edition., U.S. National Library of Medicine, 1 Jan. 1970, Available here.
2. Learning, Lumen. “Biology for Majors I.” Endocytosis and Exocytosis | Biology for Majors I, Available here.

Image Courtesy:

1. “Transcytosis of dimeric IgA and free pIgR” By Immcarle58 – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Endocytosis types” By Mariana Ruiz Villarreal LadyofHats – Own work (Public Domain) via Commons Wikimedia