- Slides: 18
Golgi Apparatus Dr. IMRANA EHSAN
Golgi Apparatus Golgi apparatus or golgi complex or simple Golgi is an organelle found in most of the eukaryotic cells. It was one of the first organelle to be discovered and observed in detail. It was first identified by an Italian physician Camillo Golgi in 1897 and is named after him as GOLGI. The discovery was confirmed in 20 th century with the invention of electron microscope.
Structure of golgi apparatus The Golgi structure is a smooth, curvy structure. It is a flattened stack of membrane enclosed sacs or cisterns with vacuoles and vesicles. It has a front end a back end. Polarized Structure show that the front end is called the cis face and the back end is called the trans face. Golgi apparatus has cisternae are the flattened membrane folds and secretory vesicles which are what the cell discharges. Number of stacks in each apparatus vary from 6 to 8.
Functions of Golgi: Plays role in packaging and processing of materials synthesized within cell, a. lysosomal enzymes b. secretory products Golgi are involved in the sorting and posttranslational modification of proteins
During the passage of proteins through the Golgi compartments, various covalent modifications take place in order to provide the specific structure and function to the protein Modification of existing glycosyl groups, O-glycosylation, sulfation (addition of sulfates to OH on tyrosine), and phosphorylation all take place within the various Golgi compartments. For simplicity, the primary focus of this lecture series will be the modification of proteins by glycosylation As mentioned previously, the ER N-glycosylates various proteins with oligosaccharides The Golgi then modifies these oligos providing either a COMPLEX OLIGOSACCHARIDE and HIGH MANNOSE CONTAINING OLIGOSACCHARIDE. The high mannose oligo is produced by removing glucose and N-acetylglucosamine moeities while the complex oligo is produced adding addition monosaccharides consecutively. Some proteins require additional oligosaccharides to provide a specific function. The Golgi also modifies proteins by O-glycosylation. Serines are used for this type of posttranslational modification.
FUNCTIONS OF GOLGI SYNTHESIS SECRETION SULFATION APOPTOSIS PHOSPHORYLATION CELL SPECIFIC FUNCTIONS
Golgi Apparatus VESICULAR TRANSPORT : The basic function of the Golgi apparatus is the transport of proteins within the cell. The Golgi receives materials for transportation through the cis face and sends the materials through to the trans face once they are packaged and modified into the vesicles. It functions in the collection, packaging, and distribution of material. The cisternae are the flattened membrane folds of the Golgi apparatus that push together pinching off secretory vesicles containing molecules which are then discharged into the cell.
Synthesis and secretion: Golgi apparatus is involved in secretion and synthesis of many different molecules within the cell eg. PROTEOGLYCANS, which are the molecules present in extracellular matrix. It is also a major site for carbohydrate synthesis eg. Glycosaminoglycans. The enzymes in golgi link several of these GAG’s.
Sulphation: Another important function of Golgi is sulfation via sulphotransferases. APOPTOSIS: a newly identified protien called GAAP (GOLGI ANTI APOPTOTIC PROTIEN)resides in Golgi and protect cell from apoptosis.
Mannose -6 phosphate targeting lysosomes: • Acid hydrolases targeted to the lysosome by a mannose-6 phosphate residue. This modification takes place in the cis-Golgi network. • Prior to modification the N-glycosyl group is modified to produce a high mannose-containing oligo. Phosphate addition to the C 6 position is catalyzed by N-acetylglucosamine phosphotransferase. This enzyme binds to and recognizes a signal patch on the folded hydrolase. The N-acetyl glucosamine is then removed to produce a mannose-6 -phosphate
Golgi Apparatus Golgi apparatus is found to play an important role in Alzheimer’s disease is a brain disorder where brain cells are being destroyed. This is what gives a person memory loss and this disease can lead to death. As the death of neurons increases the affected brain region begins to shrink. The cause of this disease is because there is too little removal of a specific type of protein. Therefore, the Golgi apparatus isn’t functioning as it is suppose to in collecting, transporting, and distributing the protein molecules.