Receptor mediated endocytosis by kk

Receptor mediated endocytosis by kk

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  By KAUSHAL KUMAR SAHU AssistantProfessor (Ad Hoc) Department of Biotechnology Govt. Digvijay Autonomous P. G. College Raj-Nandgaon ( C. G. )
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  Synopsis 1. Introduction 2. History 3.Endocytosis Pathways  Clathrin mediated endocytosis  Caveolae  Pinocytosis  Phagocytosis 4. RECEPTOR mediated endocytosis i. Types of ligands ii. Types of receptor iii. Formation of clathrin coated vesicle iv. Early endosome v. Late endosome vi. Lysosomes 5. Genetic disease  LDL Receptor 6. Conclusion 7. References
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  1. Introduction Receptor mediatedendocytosis(RME) also called clathrin dependent endocytosis, is a process by which cells internalize molecules(endocytosis) by the inward budding of plasma membrane vesicles containing protein with receptor sites specific to the molecules being internalized
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  2.History 1972- Micheal S. Brown& Joseph L. Goldstein delineated the pathway of receptor mediated endocytosis.
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  Endocytosis pathways Endocytosis pathwayscould be subdivided into 4 catagories: I. Clathrin mediated endocytosis II. Caveolae III.Pinocytosis IV.Phagocytosis I. Clathrin mediated endocytosis Clathrin mediated endocytosis is mediated by small( approx. 100 nm in diameter) vesicles that have a morphologically characteristic crystalline coat made up of a complex of protein. Eg. Low density lipoprotein(LDL) Growth factors Antibodies
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  II. Caveolae Caveolae arethe most common reported non- clathrin coated plasma membrane buds which exist on the surface of many but not all cell types. Caveolae are small (approx. 50 nm in diameter) flask shape of a cave hance the name caveolae. Eg. Adipocytes.
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  III. Pinocytosis: Pinocytosis, whichusually occurs from highly ruffled region of the plasma membrane is the invagination of the cell membrane to form a pocket. Size of vesicle(0.5-5 micro meter in diameter)
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  IV. Phagocytosis Phagocytosis isthe process by which cells bind & internalize particulate matter layer than around 0.75 micro meter in diameter. Such as small sized dust particles, cell dabris, microorganism & even apoptosis cells.
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  Receptor mediated endocytosis i.Types of ligands ii. Types of receptor iii. Formation of clathrin coated vesicle iv. Early endosome v. Late endosome vi. Lysosomes I. Types of ligands:  Biological molecules(Proteins, Corbohydrates, lipids)  Ions  Microoganisms(Viruses, Bacteria)
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  Types of Receptor: Morethan 20 different types of receptor  LDL Receptor Formation of clathrin coated vesicle:  Clathrin is a protein plays a major role in the formation of coated vesicles.  Clathrin was 1st isolated & named by Barbara Pearse in 1975.
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  Early Endosomes: Early endosomesare the 1st station of the endocytic pathway.  Vesicles up to 1 micro meter in diameter with connected tubules of approx. 50 nm in diameter.  Acidic pH (6.0-6.5) Late Endosomes: Late endosomes resive internalized material to lysosomes, usually from early endosome in the endocytic pathway, from the trans- Golgi network(TGN) in the biosynthesis pathway & from phagosomes in the phagocytic pathway. They are acidic (Approx.pH 5.5)
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  Lysosomes: Lysosomes are thelast compartment of the endocytic pathway. They are acidic pH 4.8-5.0 They have a high content of lysosomal membrane protein & active lysosomal hydrolases.
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  Genetic disease The Low– density of lipoprotein or LDL Receptor: Cholesterol is transpoted through the blood stream in the form of lipoprotein particles, the most common of which is LDL. In 1972 Michael Brown Structure of LDL
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  Familial Hypercholesterolemia(FH) FH isa genetic disease in which patients have greatly elevated level of serum cholesterol and suffer from heart attacks early in life. Michael Brown and Goldstein in1972 The Experiments: In 1974 Brown and Goldstein They investigated the binding of radio labeled LDL to fibroblast from either normal individuals or FH patients. Increasing amount of radio active LDL bound to normal cell as a function of incubation time.
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  Results:  The cellsof FH patients, failed to specifically bind radio active LDL. Accounting for the inability of LDL to inhibit HMG-coA reductase (3-hydroxy-3-methyglutaryl coenzyme A reductase)and the resultant over production of cholesterol.
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  Conclusion The human spleen& liver which are responsible for the disposal of more than 1011 aged blood cells on a daily basis. Approx. 50% of the plasma membrane is internalized receptor mediated endocytosis every hour.
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  References : THE CELL{ A Molecular Approach, Fourth Edition} Geoffrey M. Copper Robert E. Hausman  www.ncbi.com  www.cytochemistry.net/cellbiology