Endocytosis is a form of mass transport in which a cell transports molecules (such as proteins) into cells ( endo - cytosis ) by swallowing them in the process of use energy. Endocytosis and its partners, exocytosis, are used by all cells because most of the chemicals essential to them are large polar molecules that can not pass through the hydrophobic plasma or cell membranes in a passive fashion.
Endocytosis includes pinocytosis (drinking cells) and phagocytosis (eating cells).
Video Endocytosis
History
This term was proposed by De Duve in 1963. Phagocytosis was invented by ÃÆ' â € ° lie Metchnikoff in 1882.
Maps Endocytosis
Endocytosis path
Endocytosis pathways can be divided into four categories: namely, receptor-mediated endocytosis (also known as clathrin-mediated endocytosis), caveolae, macropinocytosis, and phagocytosis.
- Clathrin-mediated endocytosis is mediated by the production of small vesicles (about 100 nm in diameter) that have a distinctive morphological coat made of cathosolic protein clathrin. Clathrin-coated vesicles (CCVs) are found in almost all cells and form the domain of a plasma membrane called clathrin-coated hole. The coated holes can concentrate large molecules of different extracellular receptors responsible for receptor-mediated ligand endocytosis, such as low-density lipoproteins, transferrin, growth factors, antibodies and many others.
Studies by mammalian cells confirm the reduction of clathrin mantle size in an increasing stress environment. Additionally, this suggests that two distinctly different clathrin assembly models, ie, layered holes and coated plaques, observed in experimental investigations may be a consequence of varied tensions in the plasma membrane.
- Caveolae is the most commonly reported non-clathrin-coated plasma shoot, which is on many surfaces, but not all cell types. They consist of protein cholesterol binding guaolin (Vip21) with bilayer fortified with cholesterol and glycolipids. Caveolae is small (approximately 50 nm in diameter) pumpkin-shaped hole in a cave-like membrane (hence the name caveolae). They can form up to one-third of the plasma membrane area from multiple tissue cells, which are mainly abundant in smooth muscle, type I pneumocytes, fibroblasts, adipocytes, and endothelial cells. The absorption of extracellular molecules is also believed to be specifically mediated through receptors in guaolae.
- Potocytosis is a receptor-mediated endocytosis form that uses caveolae vesicles to carry different molecular sizes into cells. Unlike most endocytosis using caveolae to transmit vesicle contents to lysosomes or other organelles, endocytosed material via potocytosis is released into the cytosol.
- Macropinocytosis , which usually occurs from a very turbid region of the plasma membrane, is the invagination of cell membranes to form pockets, which then pinch into cells to form vesicles (0.5- 5 Ã, Âμm) filled with large volumes of extracellular fluids and molecules in them (equivalent to ~ 100 CCVs). Charging bags occur in a non-specific way. The vesicles then move into the cytosol and join other vesicles such as endosomes and lysosomes.
- Phagocytosis is the process by which cells bind and internalize particles larger than about 0.75 Âμm in diameter, such as small dust particles, cell debris, micro -organism and apoptotic cells. This process involves retrieving larger membrane areas than clathrin-mediated endocytosis and caveolae pathways.
More recent experiments have suggested that the morphological description of these endocytic events may be inadequate, and more precise classification methods may be based on clathrin dependence of certain pathways, with some subtypes of clathrin-dependent and clathrin-dependent endocytosis. Mechanical insight into non-phagocytic, chlocrin-independent endocytosis has been lacking, but recent studies have shown how Graf1 regulates the clathrin-independent endocytic pathway known as the CLIC/GEEC pathway.
The main component of the endocytic path
The endocytic pathways of mammalian cells consist of different membrane compartments, which internalize molecules from the plasma membrane and recycle them back to the surface (as in the early endosome and recycle the endosome), or sort them into degradation (as at the end of endosomes and lysosomes). The main components of endocytic pathways are:
- The beginning of endosomes is the first compartment of the endocytic pathway. The early endosomes are often on the periphery of the cell, and receive most types of vesicles originating from the cell surface. They have a characteristic tubulo-vesicular structure (vesicle diameter 1 Ã,Âμm with connected tubules of about 50 μm in diameter) and a light acid pH. They mainly sort out the organelles in which many endocytosed ligands separate from their receptors in the pH of the compartment acid, and from which many receptors recycle onto the cell surface (via the tubules). It is also a sequence to transcytotic pathways for slower compartments (such as endosomes or end lysosomes) through transvesicular compartments (such as multivesicular bodies (MVBs) or endosomal carrier vesicles (ECVs)). The endosomes endocytosed endocytosed material on the way to the lysosomes, usually from the early endosomes in the endocytic pathway, from the trans-Golgi (TGN) tissue in the biosynthetic pathway, and from phagosomes in the phagocytic pathway. End of endosomes often contain lysosomal protein characteristics, including lysosomal membrane glycoproteins and hydrolase acids. They are acidic (about pH 5.5), and are part of the trade route of the manosa-6-phosphate receptor. End of endosomes are considered to mediate the last set of sorting events before the delivery of the material to the lysosome.
- Lysosomes is the last compartment of the endocytic path. Its main function is to break down cellular waste products, fats, carbohydrates, proteins, and other macromolecules into simple compounds. This is then returned to the cytoplasm as a new cell-building material. To achieve this, lysosomes use about 40 different types of hydrolytic enzymes, all of which are produced in the endoplasmic reticulum, modified in Golgi apparatus and function in acidic environments. The approximate pH of the lysosome is 4.8 and by electron microscopy (EM) usually appears as a large vacuole (diameter 1-2Ã,Âμm) containing an electron solid material. They have a high protein content of lysosomal membrane and active lysosomal hydrolase, but no manoco-6-phosphate receptors. They are generally considered to be the main hydrolytic compartment of the cell.
It has recently been found that eisosom acts as a portal endocytosis in yeasts.
Clathrin-mediated endocytosis
The main route to endocytosis is in most cells, and the most understood is that mediated by clathrin molecules. This large protein helps the formation of a layered hole on the inner surface of the cell plasma membrane. These holes then sequester into cells to form vesicles coated in the cell cytoplasm. By doing so, it brings into the cell not only a small area of ​​the cell surface but also a small volume of fluid from outside the cell.
Coats serve to damage donor membranes to produce vesicles, and they also function in the selection of vesicle cargo. Coat complexes that have been well characterized so far include coat proteins-I (COP-I), COP-II, and clathrin. Clathrin coats are involved in two important transport steps: (i) receptor-mediated endocytosis and the fluid phase from the plasma membrane to the initial endosome and (ii) transport from TGN to the endosome. In endocytosis, the clathrin coat is strung together on the cytoplasmic surface of the plasma membrane, forming a hole that is invaginate to pinch (cut) and become free CCVs. In cultured cells, CCV assembly takes ~ 1 min, and several hundred to a thousand or more can be formed every minute. The main scaffold component of the clathrin coat is a 190-kD protein called the clathrin heavy chain (CHC), which is associated with a 25-kD protein called clathrin light chain (CLC), forming a three-foot trimmer called triskelions.
Selective vesicles concentrate and exclude certain proteins during formation and do not represent the membrane as a whole. The AP2 adapter is a multisubunit complex that performs this function on the plasma membrane. The best receptors found to be concentrated in layered mammalian cell vesicles are LDL receptors (which remove LDL from the blood circulation), transferrin receptors (which carry iron ions bound by transferrin into cells) and certain hormone receptors (such as for EGF).
At one point, about 25% of the plasma membranes of fibroblasts consist of a coated hole. Because the coated hole has a life of about a minute before it rotates into the cell, the fibroblast takes its surface by this route about once every 16 minutes. The vesicles formed from the plasma membrane have a diameter of about 36 nm and the lifetime is measured in a few seconds. Once the mantle is released, the remaining vesicles join the endosome and progress to the endocytic pathway. The actual beginner process, in which the hole is converted to vesicles, is performed by clathrin aided by a set of cytoplasmic proteins, which include dynamins and adapters such as adaptin.
The coated holes and vesicles were first seen on the thin part of the network in the electron microscope by Matt Lions and Parker George. Their importance for cleansing LDL from blood was discovered by Richard G. Anderson, Michael S. Brown and Joseph L. Goldstein in 1977. Coated vesicles were first purified by Barbara Pearse, who invented the molasses of clathrin coats in 1976.
See also
- Active transport
- Emperipolesis
- Exocytosis
- Phagocytosis
- Pinocytosis
References
External links
- A comprehensive review of endocytosis and endocytic mechanisms by Doherty and McMahon
- Endocytosis at biologyreference.com
- Endocytosis - examines the endocytic mechanisms at endocytosis.org
- Endocytosis of ASCB mediated by Clathrin Image & amp; Video Library
- Type of Endocytosis (Animation)
Source of the article : Wikipedia
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