Main Difference – Endocytosis vs Phagocytosis
Endocytosis and phagocytosis are two mechanisms involved in taking in material into the cell. Endocytosis contains two categories: phagocytosis and pinocytosis. This matter that is taken into the cell could be enzymes, hormones, nutrients, ions, cell debris, dead cells or even bacteria like pathogens inside the body of a multicellular organism. Both endocytosis and phagocytosis form vesicles, surrounding the uptaken matter. Exocytosis is involved in the elimination of waste substances, which are produced by the digestion inside these vesicles. The main difference between endocytosis and phagocytosis is that endocytosis is taking in of matter into a living cell by forming vesicle by the cell membrane whereas phagocytosis is taking in of large solid matter into the cell by forming phagosomes.
This article looks at,
1. What is Endocytosis
– Definition, Characteristics, Features
2. What is Phagocytosis
– Definition, Characteristics, Features
3. What is the difference between Endocytosis and Phagocytosis
What is Endocytosis
Endocytosis is the process of taking in material into a cell by the formation of vesicles surrounding the relevant material. This material to be taken in can be either macromolecules or particles. They are surrounded by an area of the plasma membrane, pinching off inside the cell, forming an endocytic vesicle. Endocytosis is composed of three categories: phagocytosis, pinocytosis and receptor-mediated endocytosis. Phagocytosis and pinocytosis differ by the size of the vesicle which is formed by the process. During phagocytosis, large, solid materials are taken into the cell, forming a large vesicle, called phagosome.
During pinocytosis, fluids, along with its solutes, are taken in, forming a small vesicle called the pinosome. Pinocytosis occurs in almost all the cells in the body of a multicellular organism. Clathrin-coated pits in the plasma membrane are involved in the formation of pinosomes. The resultant vesicle also contains a clathrin-coated membrane. But, some of the pinocytic pathways lack clathrin-coated vesicles. Pinocytosis is considered as a continuously occurring process. During receptor-mediated endocytosis, macromolecules in the extracellular fluid are recognized by the specific receptors in the plasma membrane. Some of the extracellular macromolecules like cholesterol are uptaken by receptor-mediated endocytosis while increasing the efficiency of this process. The types of endocytosis are shown in figure 1.
Figure 01: Endocytosis types
What is Phagocytosis
Phagocytosis is the one mechanism of taking in material during endocytosis, which can be described as the ingestion of large solid particles by the cell. During phagocytosis, particles like cell debris, aged cells, small mineral particles, dust, various colloids and bacteria are taken up by the cell. The immune system cells like tissue macrophages, neutrophils and monocytes are considered as professional phagocytes. Phagocytic cells can also be found in Langerhans cells in the skin, Kupffer cells in the liver, the pigmented epithelium of the eye and the microglia in the brain. However, phagocytosis is involved in the defense mechanisms, which destroy pathogenic material found in the body. Phagocytosis is also a receptor-mediated process. Some of the receptors that are involved in the process are immunoglobulin G, mannose (MR), β-glucan and complement (CR1, CR3). Hence, it is considered as a triggered process.
Phagocytic cells form pseudopodia by surrounding the particle to be uptaken. Then plasma membrane is pinched off into a phagocytic vesicle, which is called a phagosome. Phagosomes are capable of fusing with lysosomes, forming the phagolysosomes. The material inside the phagolysosome is digested by the enzymes in the lysosome. Digestive waste is eliminated by exocytosis. Phagocytosis is also called as cell eating in single-celled organisms. Protozoans like amoeba uptake nutrients by phagocytosis. Phagocytosis is shown in figure 2.
Figure 2: Phagocytosis
Difference between Endocytosis and Phagocytosis
Definition
Endocytosis: Endocytosis refers to taking in of matter into a living cell by the forming of a vesicle by the cell membrane.
Phagocytosis: Phagocytosis refers to the taking in of large solid matter into the cell by forming phagosomes.
Correspondence
Endocytosis: Endocytosis is composed of three categories: phagocytosis, pinocytosis and receptor-mediated endocytosis.
Phagocytosis: Phagocytosis is a category of endocytosis.
Material taken up
Endocytosis: During endocytosis, both macromolecules and particles are taken into the cell.
Phagocytosis: During phagocytosis, only particles are taken into the cell.
Conclusion
Endocytosis is the taking in of matter into the cell for various metabolic purposes. It is categorized into three types of mechanisms, based on the distinct types of material taken in. Large solid particles like cell debris, dead cells, and bacteria-like pathogens are taken up by phagocytosis. Phagocytosis is involved in the defense mechanisms of the cell. Fluids and dissolved solutes in it are taken up by pinocytosis. Almost all the cells in the body take in nutrients, ions, and other macromolecules into the cell by pinocytosis. The third and the most specific mechanism of endocytosis is receptor-mediated endocytosis. During receptor-mediated endocytosis, receptors in the plasma membrane identify the macromolecules like cholesterol in the extracellular fluid. However, the main difference between endocytosis and phagocytosis is their correlation of the mechanisms.
Reference:
1. Alberts, Bruce. “Transport into the Cell from the Plasma Membrane: Endocytosis.” Molecular Biology of the Cell. 4th edition. U.S. National Library of Medicine, 01 Jan. 1970. Web. 31 Mar. 2017.
2. Cooper, Geoffrey M. “Endocytosis.” The Cell: A Molecular Approach. 2nd edition. U.S. National Library of Medicine, 01 Jan. 1970. Web. 31 Mar. 2017.
Image Courtesy:
1. “Endocytosis types” By Mariana Ruiz Villarreal LadyofHats – Own work (Public Domain) via Commons Wikimedia
2. “Phagocytosis2” By GrahamColm at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia
Leave a Reply