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OUTLINEIntroductionDiscoveryMorphology Cisternae Cis-Face Trans-FaceFunctionsWorking Of Golgi ComplexTransportation
GOLGI COMPLEX A membranous complex ofvesicles, vacuoles, andflattened sacs in the cytoplasmof most cells involved inintracellular secretion andtransport. Found in most eukaryoticcells. Golgi Complex sometimealso called as the Golgi Bodyor Golgi Apparatus
DISCOVERYGolgi apparatus is named after thescientist who discovered it.Camillo Golgi was an Italian biologistwho discovered this organelle with a lightmicroscope in 1898.He developed a method that stained itintensely and made possible thedemonstration of its occurrence in a widevariety of cell types.This method is known as Golgi Stainingor Golgi Impregnation.
MORPHOLOGYThe Golgi is composed of stacksof membrane-bound structuresknown as Cisternae.A cisterna (plural cisternae)comprises a flattened membranedisk that makes up the Golgiapparatus.Usually a Golgi has 6-7 cisternae.Each Golgi stack has a distinctorientation.A complex network of tubulesand vesicles is located at theedges of these cisternae.
MORPHOLOGY• The cisternae stack has Two faces : Cis-Golgi Trans-Golgi
CIS-GOLGI The side faces the Endoplasmic reticulum is Cis Face and is the entry face that receives small membrane vesicles from the ER. Vesicles from the endoplasmic reticulum fuse with the cis-Golgi network and subsequently progress through the stack to the trans-Golgi network. The cis is the site at which transport vesicles bringing newly synthesized products from the endoplasmic reticulum with and add their contents to the Golgi cisternae. A complex network of anatomizing (connecting) membrane tubules attach to and cover cisternae on the cis face and serve as a docking site for transport vesicles. Each region contains different enzymes which selectively modify the contents depending on where they are destined to reside.
TRANS-GOLGI The side faces the cell membrane is Trans Face and is the exit face where vesicles leave the Golgi and move to their targets, including the exterior of the cell. As the last station of the Golgi complex, the trans-Golgi network (TGN) plays a pivotal role in directing proteins in the secretary pathway to the appropriate cellular destination. Proteins synthesized on membrane-bound ribosomes are transported through the Golgi apparatus and, on reaching the trans-Golgi network, are sorted for delivery to various cellular destinations. Sorting involves the assembly of cytosol-oriented coat structures which preferentially package cargo into vesicular transport intermediates. Protein sorting into different transport vesicles requires specific interactions between sorting motifs on the cargo molecules and vesicle coat components that recognize these motifs.
FUNCTIONS The Golgi apparatus is integral in modifying, sorting, and packagingmacromolecules for cell secretion (exocytosis) or use within the cell. It primarily modifies proteins delivered from the rough endoplasmicreticulum, then sends the modified macro-molecules to different partsof the cell or outside of the cell. It is also involved in the transport of lipids around the cell, and thecreation of lysosomes. In this respect it can be thought of as similarto a post office; it packages and labels items which it then sends to different parts of the cell.
FUNCTIONS The Golgi plays an important role in the synthesis of proteoglycans, which are molecules present in the extracellular matrix of animals. It is also a major site of carbohydrate synthesis. A newly characterized protein, GAAP (Golgi anti-apoptotic protein), almost exclusively resides in the Golgi and protects against cell destruction known as apoptosis by an as-yet undefined mechanism. Sometimes vital proteins needed in the rough endoplasmic reticulum are transported along with the other proteins in the Golgi complex. The Golgi complex has a mechanism for trapping them and sending them back to the rough endoplasmic reticulum.
WORKING OF GOLGI COMPLEX Proteins are translated and modified with in the rough endoplasmic reticulum. In order to complete their modifications, they are transported in membrane-bounded vesicles to the cis side of the Golgi apparatus. Transport vesicles from the rough ER fuse together and become the cis cisterna of the Golgi.
WORKING OF GOLGI COMPLEX Once they reach the Golgi apparatus, additional modifications are made to the transported proteins by resident Golgi enzymes. These modifications are key in ensuring the proteins reach their final destinations once they leave the Golgi apparatus. The Golgi apparatus is divided into distinct regions. These include the cis cisterna, nearest the ER, the centrally located medial cisternae, the trans cisterna, and the trans Golgi Network (TGN).
WORKING OF GOLGI COMPLEX According to the cis maturation model, the proteins are transported through the Golgi stack as the cisterna containing them migrate, or mature, in a cis-to-trans direction. New vesicles from the ER continually supply new cis cisterna as trans Golgi network vesicles mature. Within the trans Golgi network, proteins are sorted by their final destinations. This is accomplished by receptor molecules embeddedin the membrane of the TGN.
WORKING OF GOLGI COMPLEX When proteins have reached their correct location within the TGN, the membrane at those locations buds off into vesicles. More than one protein can be contained within each transport vesicle. Once released, the vesicles carry their cargo proteins to a final location. Possible destinations include the lysosome, the digestive organelle of the cell, and the plasma membrane, where the proteins can be released elsewhere in the organism.
TRANSPORTATION The flow of cargo proteins through Golgi apparatus is from cis to trans. Despite this flow there are many resident proteins that are localized in particular parts of the Golgi. How newly produced proteins travel from the ER to the Golgi complex and travel among Golgi stacks while the resident proteins stay in place ? Vesicle Transport Model Cisternal Maturation Method
TRANSPORTATION • Cisternal Maturation Method• Created by Jennifer Lippincott Schwartz from the National Institute of Child health and human development.• The cis-most cisterna is the youngest, having been recently formed from incoming vesicles• The trans-most cisterna is the oldest and breaks up into vesicles as material is moved to the trans Golgi network• Cargo proteins are carried with the cisterna; resident proteins are returned to their proper location by retrograde movement of vesicles.
TRANSPORTATIONVesicle Transport Model• This Model was created by Gram Warren of Yale School of medicine• One model suggests that proteins are transported enclosed in vesicles. Another model proposes that one stack of the Golgi "matures" into the next stack.• Cargo proteins (but not resident proteins) are moved from stack to stack by vesicle transport.• This sorting also involves both forward, anterograde (cis to trans), and backward, or retrograde (trans to cis), flow of vesicles with proteins, moving back up the stack.• Resident proteins that are carried to locations trans to their normal location are transported back by retrograde movement of vesicles
TRANSPORTATIONCisternal Maturation Method Vesicle Transport Model