It was discovered in by Italian physician Camillo Golgi during an investigation of the nervous system. Some doubted the discovery at first, arguing that the appearance of the structure was merely an optical illusion created by the observation technique used by Golgi. With the development of modern microscopes in the 20th century, the discovery was confirmed. In mammals, a single Golgi apparatus is usually located near the cell nucleus , close to the centrosome. Tubular connections are responsible for linking the stacks together.
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Abstract Glycosylation is a very common modification of protein and lipid, and most glycosylation reactions occur in the Golgi. Although the transfer of initial sugar s to glycoproteins or glycolipids occurs in the ER or on the ER membrane, the subsequent addition of the many different sugars that make up a mature glycan is accomplished in the Golgi. Golgi membranes are studded with glycosyltransferases, glycosidases, and nucleotide sugar transporters arrayed in a generally ordered manner from the cis-Golgi to the trans-Golgi network TGN , such that each activity is able to act on specific substrate s generated earlier in the pathway.
The spectrum of glycosyltransferases and other activities that effect glycosylation may vary with cell type, and thus the final complement of glycans on glycoconjugates is variable.
In addition, glycan synthesis is affected by Golgi pH, the integrity of Golgi peripheral membrane proteins, growth factor signaling, Golgi membrane dynamics, and cellular stress. Knowledge of Golgi glycosylation has fostered the development of assays to identify mechanisms of intracellular vesicular trafficking and facilitated glycosylation engineering of recombinant glycoproteins.
The Golgi is home to a multitude of glycosyltransferases GTs , glycosidases, and nucleotide sugar transporters that function together to complete the synthesis of glycans from founding sugars covalently attached to protein or lipid in the endoplasmic reticulum ER Fig. Thus, glycoproteins, glycosphingolipids GSLs , proteoglycans, and glycophosphatidylinositol GPI anchors acquire their final sugar complement during passage through the Golgi. Most glycoproteins and proteoglycans are either secreted from the cell, or span the plasma membrane with their glycans becoming the molecular frontier of the cell Fig.
GSLs and GPI-anchored proteins also reside in the plasma membrane, the latter being confined to the outer leaflet of the lipid bilayer. The forest of glycans at the cell surface is often called the glycocalyx and can be visualized by electron microscopy after staining for sugars.
Appareil de Golgi