Difference Between Endocytosis and Receptor Mediated Endocytosis

The key difference between endocytosis and receptor mediated endocytosis is that endocytosis is a cellular mechanism by which cells take in substances inside the cell by forming vesicles. Meanwhile, receptor-mediated endocytosis is a form of endocytosis in which receptors located on the cell surface are used to capture specific target molecules such as metabolites, hormones, proteins, etc.

Endocytosis is a cellular process which helps to take in substances into the living cell by invagination of its membrane to form a vesicle. Phagocytosis, receptor-mediated endocytosis, and pinocytosis are three forms of endocytosis. Pinocytosis is the ingestion of liquid into cells by budding of small vesicles from the cell membrane. Receptor-mediated endocytosis is a process which absorbs specific molecules and viruses inside the cell, recognizing the molecules by receptors located in the cell membrane and then by forming small vesicles from the cell membrane. Phagocytosis ingests large solid matters, such as cell debris, pathogens such as bacteria, dead cells, dust particles, small mineral particles, etc., into the cell by forming phagosomes.

CONTENTS

1. Overview and Key Difference
2. What is Endocytosis 
3. What is Receptor-Mediated Endocytosis
4. Similarities Between Endocytosis and Receptor-Mediated Endocytosis
5. Side by Side Comparison –  Endocytosis vs Receptor-Mediated Endocytosis 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 such as bacteria, dead cells, dust particles, small mineral particles, etc., into the cell by forming phagosomes. Most immune cells, including tissue macrophages, neutrophils and monocytes are professional phagocytic cells. Generally, phagocytosis is a defence mechanism which destroys 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 which 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, described with details in the below section.

What is Receptor-Mediated Endocytosis?

Receptor-mediated endocytosis is a form of endocytosis in which macromolecules are taken inside the cell selectively from the extracellular fluid. This mechanism is mediated by receptors located on the cell surface and specific binding with the macromolecules outside the cell. Receptors which are involved with receptor-mediated endocytosis concentrate in clathrin-coated pits. Extracellular macromolecules bind with receptors and internalize into clathrin-coated vesicles formed from clathrin-coated pits. The clathrin-coated vesicles then fuse with early endosomes; their contents are sorted for transport to lysosomes or recycling to the plasma membrane.

Receptor-mediated endocytosis is a very specific mechanism for taking in molecules into cells, unlike pinocytosis. Materials which are transported inside are decided by the receptors present on the cell membrane surface. Furthermore, it is a more efficient process than pinocytosis.

What are the Similarities Between Endocytosis and Receptor-Mediated Endocytosis?

• Receptor-mediated endocytosis is a form of endocytosis.
• They are cellular processes.
• Both mechanisms facilitate the uptake of materials inside the cell.
• These mechanisms form membrane coated vesicles.

What is the Difference Between Endocytosis and Receptor Mediated Endocytosis?

Endocytosis is a cellular mechanism that moves particles into a cell by enclosing them in a vesicle made out of plasma membrane, while receptor-mediated endocytosis is a form of endocytosis mediated by the receptors located on the cell surface. So, this is the key difference between endocytosis and receptor mediated endocytosis. There are three forms of endocytosis as phagocytosis, pinocytosis and receptor-mediated endocytosis, but there are no subtypes of receptor-mediated endocytosis.

Moreover, endocytosis takes in selective and nonselective substances into the cell, while receptor-mediated endocytosis is more specific, and it selects specific target macromolecules to enter the cell. Therefore, this another difference between endocytosis and receptor mediated endocytosis.

Summary – Endocytosis vs Receptor-Mediated Endocytosis

Endocytosis is an active transport mechanism that uptakes particles into a cell by enclosing them in a vesicle made out of plasma membrane. There are three forms of endocytosis. Among them, receptor-mediated endocytosis is one form, and it is done via the receptors present on the cell surface. Hence it is different from the other two forms of endocytosis. Phagocytosis and pinocytosis are the two other forms of endocytosis. Thus, this summarizes the difference between endocytosis and receptor mediated endocytosis.

Reference:

1.“Bulk Transport (Article).” Khan Academy, Available here.
2. Gao, Huajian, et al. “Mechanics of Receptor-Mediated Endocytosis.” PNAS, National Academy of Sciences, 5 July 2005, Available here.

Image Courtesy:

1. “Endocytosis types” By Mariana Ruiz Villarreal LadyofHats – Own work (Public Domain) via Commons Wikimedia
2. “Itrafig2” By Grant, B. D. and Sato, M – (Transferred from en.wikipedia to Commons by Vojtech.dostal.) (CC BY 2.5) via Commons Wikimedia