Golgi Apparatus (2019-2020) Oran 1 University PDF

Machine Translated by Google Oran 1 University, Faculty of Medicine, Department of Medicine, Histology-Embryology Department Dr Hamadouche H Dr Belarbi-Amar N Cytology course of the first year of Medicine...

Machine Translated by Google Oran 1 University, Faculty of Medicine, Department of Medicine, Histology-Embryology Department Dr Hamadouche H Dr Belarbi-Amar N Cytology course of the first year of Medicine The endomembrane system: Golgi apparatus I. General: The Golgi apparatus ÿ is described by Camillo Golgi in 1898 in nerve cells. ÿ is a major organelle found in almost all cells. ÿ made up of a complex network of smooth membranes, grouping dictyosomes, consisting of a stack of flattened saccules. ÿ represents the obligatory passage point for all proteins synthesized in the Golgi apparatus. ÿ is an essentially dynamic structure, located around the nucleus and near the centrosome. The position of the Golgi is correlated with that of the microtubules, since their depolymerization by chemical agents results in a dispersion of the Golgi. He intervenes: ÿ in the transfer of proteins from the endoplasmic reticulum to the secretory grains intended for exocytosis. ÿ in protein maturation: glycosylation, phosphorylation, sulfation, etc. ÿ in sorting, packaging and targeting of the products produced so that they reach their final destination (lysosomes, plasma membrane, nucleus, etc.). II. Structure : 1. In optical microscopy : The Golgi apparatus is not visible on usual sections, but can be selectively stained by silver impregnation. It forms an irregular network. The shape and size vary depending on the cell type and activity. It is highly developed in active cells such as glandular cells and nerve cells, and poorly developed in resting or hypoactive cells (muscle cells). 2. In electron microscopy : it includes a set of dictyosomes. 1 Academic year: 2019-2020 Machine Translated by Google Oran 1 University, Faculty of Medicine, Department of Medicine, Histology-Embryology Department Dr Hamadouche H Dr Belarbi-Amar N Cytology course of the first year of Medicine Each dictyosome is formed by saccules: vesicles and tubules. The saccule is the elementary structural unit of the dictyosome. It is curved with dilated edges (with a diameter of 0.5 to 1 Um) surrounded by a tristratified membrane. The number of saccules in a dictyosome averages between 3 and 10, but may increase in highly active cells. Golgi apparatus in electron microscopy (7) Polarity of dictyosomes : Each dictyosome is polarized and has two faces: - a "cis" face: in relation to the RER, convex. - and a "trans" face: opposite, turned towards the secretion grains, concave. Each dictyosome is surrounded by vesicles that bud from the saccules and transport substances. Each dictyosome is subdivided into three different functional regions: -saccules of the cis face or CGN face (Cis Golgi Network), also called the entry face. These saccules are supplied by an intermediate material with the endoplasmic reticulum ERGIC (Endoplasmic Reticulum-Golgi intermediate Compartment). - saccules of the median region. -a saccule of the trans face or exit face in continuity with a network of canaliculi constituting the TGN (Trans Golgi Network). 2 Academic year: 2019-2020 Machine Translated by Google Oran 1 University, Faculty of Medicine, Department of Medicine, Histology-Embryology Department Dr Hamadouche H Dr Belarbi-Amar N Cytology course of the first year of Medicine III. Fonctions : 1. Post-translational modifications of proteins originating from the Golgi apparatus: 3 Academic year: 2019-2020 Machine Translated by Google Oran 1 University, Faculty of Medicine, Department of Medicine, Histology-Embryology Department Dr Hamadouche H Dr Belarbi-Amar N Cytology course of the first year of Medicine Secretory pathways of the Golgi apparatus (7) - La O-glycosylation : O-glycosylation takes place in the Golgi apparatus, more precisely in the medial and trans saccules. In this glycosylation, the glycosylated chain is transferred to the oxygen carried by the amino acid serine or threonine of the protein by an o-glycosyl transferas Unlike N-glycosylation, the oligosaccharide chain is not necessarily linked by an N acetyl glucosamine group. Furthermore, the composition of the glycosylated chain is very variable. 4 Academic year: 2019-2020 Machine Translated by Google Oran 1 University, Faculty of Medicine, Department of Medicine, Histology-Embryology Department Dr Hamadouche H Dr Belarbi-Amar N Cytology course of the first year of Medicine La O-glycosylation - Packaging of secreted products: Proteins synthesized in the ER travel through the Golgi apparatus, thanks to transition vesicles. They enter the Golgi apparatus through the Cis face (CGN), transit through the medial saccules and reach the trans saccules. They are then packaged in secretory vesicles. - Phosphorylation : Modification essential for the maturation of soluble enzymatic glycoproteins (N glycosylated) in lysosomes and their targeting to this compartment. It takes place in the Cis saccules of the Golgi apparatus and occurs in two stages: -an N-acetyl-glucosamine phosphotransferase attaches the N-acetyl-glucosamine-phosphate to carbon 6 of the mannose residue of the glycoprotein. -a second enzyme comes into play, N-acetyl-glucosamine phospho-glucosidase releases the N-acetyl-glucosamine and leaves the phosphate linked to carbon 6 of the mannose of the glycoprotein. -Sulfation: Secreted proteins are frequently sulfated. The SO4-- group is added either to tyrosine residues or to glycosylated chains resulting from N-glycosylation using a sulfotransferase. 5 Academic year: 2019-2020 Machine Translated by Google Oran 1 University, Faculty of Medicine, Department of Medicine, Histology-Embryology Department Dr Hamadouche H Dr Belarbi-Amar N Cytology course of the first year of Medicine Sulfation occurs in the trans saccules of the Golgi apparatus. Ex: proteoglycans. N-acetyl-glucosamine phosphotglucosidase N-acetyl- glucosamine phosphotransférase Phosphorylation of enzymatic glycoproteins (7) (1) Bibliographic references: 1. Cellular Biology. Abstracts. Marc Maillet. 9th edition, Masson2002. 2. Cellular Biology. Y Bassaglia. Maloine 2001. 6 Academic year: 2019-2020 Machine Translated by Google Oran 1 University, Faculty of Medicine, Department of Medicine, Histology-Embryology Department Dr Hamadouche H Dr Belarbi-Amar N Cytology course of the first year of Medicine 3. Cellular biology and physiology. A. Berkaloff, Bourguet, Favard, Lacroix. Herman. 1978. 4. Cellular Biology Course: Pierre Cau, Raymond Seite. Edition ellipses.1999. 5. Cytology & Cellular Physiology. M. Abdelali, H. Benzine-Challam, A.Madoui- Dekar. Office of University Publications 2008. 6. Histologie. « Bloom & Fawceett ».D W Fawcett, R P Jensh. Maloine.2002 7. The cell and its physiology: M Bendjelloul. Office of University Publications 2011. 8. The cell. A molecular approach. Geoffrey M. Cooper. Edition De boeck university 1999. 9. Mini manual of Cellular Biology: QCM course, QROC. JM Petit, S Arico, R Julien. Dumond 2008. 7 Academic year: 2019-2020