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Lecture 8

Lecture 8

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University of Toronto St. George
Darrel Desveaux

Thursday January 29, 2009 - This is the next lecture, this is about sorting and packaging of proteins in the Golgi apparatus. - Just an overview, this is basically to remind us of how proteins destined for the secretion pathway actually go through this process and well see a little movie of this in a bit. Basically all proteins or most of them are transcribed, the genes are transcribed in the nucleus and then translated in the cytoplasm and proteins that are destined for secretion are transported into the ER shown on the slide. - That is the 1 stage, they get in there by transmembrane transport & then the 2nd stage is mo vement from the ER to the Golgi & this is thro u g h vesicular transport so that is what were going to cover today, is how proteins move from the ER to the Golgi through the Golgi & then sorted to different compartments & we will focus on the lysosome today. - Re co giz e or ap pre iate that both solu b le proteins & transmembrane proteins are going through this secretion process. - So the 1 destination from the ER is the Golgi and that is what were going to cover today and this movie nicely shows what we learned so far about secretion and where were going to. Movie - Fluorescently labeled membrane proteins start their journey to the plasma membrane after synthesis in the ER. They are first dispersed throughout the extensive membrane network of the ER. - From there they move to exit sites that form in rando m locations in the membrane network. At each of these sites, the membrane proteins are concentrated and packaged into transport vesicles. Clusters of the transport vesicles fuse to form transport intermediates. - At the next stage, transport intermediates move along microtubule tracts to the Golgi apparatus near the center of the cell. The membrane proteins exit the Golgi apparatus. - They mo v e in transp ort vesicles that are now pul e ld outward by the microtubules which deliver them to the plasma membrane. Each time a Golgi derived vesicle fuses with the PM, its content proteins disperse. - That video nicely shows well first movement in the cell and how proteins get through the secretion pathway so were going to start with the movement from the ER to the Golgi. - First just to give us an overview of what the Golgi looks like, were all familiar with this structure but basically you would have the ER up there and movement of proteins is going from the ER to the first part of the Golgi which is called the cis Golgi. - The Golgi can be separated into different cisternae, so these are different layers of the Golgi. The first one that is encountered would be the cis Golgi network or the CGN. That leads into the cis Golgi, this cis Golgi network is the closest one to the ER and that would be called the cis face of the Golgi that moves to the trans cisternae and eventually to this complex structure of membranes and vesicles called the trans Golgi network. From there vesicles or proteins are sorted to their appropriate compartments in the cell like the
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