Explore The Top 8 Functions of Golgi Apparatus

The Golgi Apparatus was discovered by biologist Camillo Golgi in 1898 during an experiment that involved staining neuronal cells. It was described as an intracellular reticular compartment inside the cell.

• Following this discovery, in 1900, Golgi, Negri, and Cajal attempted to stain and visualize this compartment in many other different kinds of cells.
• This discovered structure has initially coined the term “The reticular structure of Golgi“. The term popularly used today “Golgi Apparatus” was coined by Nusbaum in the year 1913.
• The primary role of the Golgi Apparatus in protein secretion was first proposed by Fuchs in the year 1902. Eventually, experiments carried out by Nassonov and Bowen provided evidence for this statement. However, several different scientists tried to disprove this theory and label the Golgi apparatus as a non-functional artifact of the eukaryotic cell.
• Until the year 1950, scientists continued to debate on the functionality of the Golgi apparatus, until some scientists elaborated its role using the electron microscope.

• Protein processing events for glycoproteins within the Golgi apparatus comprises of a series of events that terminates in modification or glycosylation of the carbohydrate moieties of the protein structures.
• In the ER, the proteins undergo post-translational modifications. One such modification includes the addition of N-linked oligosaccharides to these proteins. Processing of these carbohydrate moieties occurs in the Golgi Apparatus.
• The very first step in the modification of these proteins in the Golgi Apparatus is the removal of mannose residues. Following this, N-acetylglucosamine is added, and two more mannose residues are removed.
• In the next step, fucose and two more N-acetylglucosamine residues are added. Finally, three galactose and three Sialic acid residues are added.
• This process of modification may differ from protein to protein and in different kinds of cells depending on the number of modification enzymes present in the Golgi Bodies.

• The modification of lysosomal proteins begins within the cis-Golgi network itself.
• In this process, N-linked oligosaccharides of lysosomal proteins are modified sequentially by addition of phosphate moieties to mannose residues and the removal of N-acetylglucosamine.
• This process leads to the formation of mannose-6-phosphate residues on the protein that are later recognized by mannose-6 phosphate receptors present in the trans-Golgi network. This ensures proper packaging and transport of these proteins to the lysosomes.

• The Golgi Apparatus is responsible for the metabolism, in particular, the synthesis of glycolipids and sphingomyelin.
• Sphingomyelin is synthesized in the lumen of the Golgi Apparatus, and ceramide is added to it in the cytosol of the Golgi Apparatus.
• They are then transported using vesicular transport to the exterior.

• Plant cell walls are composed of three main types of carbohydrates: Cellulose, hemicellulose, and pectin.
• Complex branched-chain polysaccharides such as hemicellulose and pectin are synthesized in the Golgi Apparatus.
• After synthesis, these complex carbohydrates are packaged into vesicles are transported to the surface as part of the cell wall.

• Proteins, lipids, and other molecules are transported from and to the Golgi apparatus using the secretory pathway.
• This pathway involves tiny transport vehicles called vesicles which bud off from the trans face of the Golgi apparatus and are then transported to their respective locations.
• Some proteins are packaged and delivered to the cell membrane, which then incorporates these proteins as a part of the plasma membrane.

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• Exocytosis is a transport and secretory pathway that makes use of vesicles to transport substances from the Golgi to other organelles.
• Following the processing and modification of proteins in the Golgi Apparatus, they are stored in membrane-bound storage structures known as vesicles, which are then transported to other organelles, cellular compartments, the plasma membrane or the cytoplasm.
• This entire exocytic pathway is known as the outward pathway.
• Unique proteins known as the SNARE proteins are responsible for docking the vesicles to membrane SNARE receptors present in the plasma membrane. This mechanism allows the vesicles to either fuse with the plasma membrane or releases the proteins to the exterior.

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• Endocytosis is a vesicular transport pathway that makes use of vesicles to transport materials into the Golgi apparatus for processing or modification.
• The process of endocytosis begins with the formation of an inward bud-like structure at the plasma membrane. The particle to be ingested is then engulfed by this structure and completely enclosed.
• It is then released into the cell to carry out its function, or to undergo further processing or modification.
• There are two kinds of endocytic pathways – Phagocytosis that ingests materials larger than 250nm in diameter, and pinocytosis – that ingests liquid particles and smaller materials of about 100nm diameter.

• From the trans-golgi network, materials are sent out to three main locations: Within the cell to lysosomes, Plasma membrane and to the outside of cells.
• The transportation of different proteins depends on their function. Each material that is transported has receptors or biomolecules on its surface that tags or directs it to its appropriate location.
• At the receiving end, receptors that recognize these tags allow these membrane-bound materials to fuse with the plasma membrane of the destination and release the contents into the destination cell.