weber uiuc edu 31 October 2007 MCB150 Lecture 28 Lecture 28 31 October 2007 Announcements More broken hand notes Exam III is two weeks away Regarding Monday s lecture content o 10 mers aren t 10 mers anymore They re 11 mers now o After N linked glycosylation the tree has 11 saccharides on them You start with 14 mers and reduce down to 11 mers This is new research o If on the exam it will be 11 mer not 10 mer o The only thing that has changed is the trimming steps You only trim off 3 Still start off with 14 mer on dolichol o Before the protein that has been glycosylated is ready to move on it is processed which leaves you with an 11 mer on there o He won t try to trick us There may be 14 and 11 in a question but not a trick between 11 and 10 o THIS WAS EDITED INTO THE PREVIOUS SET OF NOTES WHEN HE SAID 10 MER IT WAS CHANGED TO 11 MER Translated Folded Modified Proteins What happens in the rough ER o In the RER you will usually be glycosylated o Perhaps added onto a GPI anchor or a disulfide bond added Now typically the protein presents the glycosylated signal The signal tells the cell that you are ready to move on We ve seen the pathway in the Pulse Chase experiment Now we are ready to move on to the Golgi apparatus We will continue working on the protein but not in the ER Golgi Apparatus How do you get to the Golgi o Is the Golgi connected to the ER No The Golgi is separate there is no direct path from the ER to the Golgi o Have to actually move outside the ER Use transport vesicles to move from the ER to the Golgi o Vesicles will allow us to pack up stuff to move o Vesicles are membrane bound fluid filled spheres o Wrap the protein in some membrane The content will move from A B Perhaps eventually to the outside of the cell o Need to get to the Golgi first The vesicles bud off the ER o Pinch off a bubble of membrane from the ER with stuff inside Important what starts lumenal stays lumenal What starts cytosolic will stay cytosolic o This does not change o A soluble protein in the lumen of the ER will never touch the cytoplasm Page 1 of 7 weber uiuc edu 31 October 2007 MCB150 Lecture 28 o If in the lumen of the ER you will be in the lumen of the vesicle From there you will be in the lumen of the Golgi and so forth o Something that is supposed to be in the inside of the Golgi has to start in the lumen of the ER o In the end topologically speaking the extracellular space is functionally equivalent to the lumen of the ER Golgi etc This is in terms of surfaces and chemical composition o How is this so Note that there is a difference between the outside of an organelle the cytoplasm and outside the cell the extracellular space How does the ER protein get to the Golgi Budding A vesicle will bud off from the ER Like blowing a bubble Whatever is trapped inside is cargo The bubbles come together melting into one larger space o Small spheres join up dumping their contents into the lumen of the Golgi o You simply dump your contents into the lumenal space KNOW THIS If you are a membrane protein the part that faces the cytosol will always face the cytosol The parts that face the lumen will face the lumen of the Golgi DIAGRAM o The proteins in the membrane will still be in the membrane of the Golgi or other vesicle o The parts that are in the cytoplasm stay in the cytoplasm When you package up a transport vesicle the proteins in the lumen will be in the interior of the vesicle o When it fuses the proteins on the inside are dumped into the interior of the larger membrane bound vesicle o You fuse by allowing your lipids come together with the other organelle s where they will fuse naturally o The contents then mix o The size of the contents do not matter When the vesicle reaches the cell membrane what happens o The contents are dumped into the extracellular space o It opens and the interior of the vesicle ends up on the outside of the plasma membrane o The transmembrane proteins which face the lumen now face the extracellular space o Same with the soluble contents of the lumen they are now in the extracellular space o This is how proteins are secreted o This is why secreted proteins are processed in the ER They have to be worked on in the lumen so they can end up on the outside of the cell o The membrane components become part of the cellular membrane or the membrane of the organelle o Signals will instruct the vesicles where to go Page 2 of 7 weber uiuc edu 31 October 2007 MCB150 Lecture 28 The Golgi Apparatus and the Secretory Pathway When you leave the ER the next structure where you see the radio labeled proteins from the Pulse Chase experiment is the Golgi o The Golgi is in layers like pancakes o When you leave the ER you are headed to the Golgi The Golgi is relatively small There is far more membrane in the ER than in the Golgi o Therefore it is likely that the vesicles will run into each other and fuse forming an intermediate compartment o Odds are the longer the distance the more likely it is that you will form an ERGIC ER Golgi Intermediate Complex Compartment o EXAM Functionally speaking there is nothing new happening in the ERGIC o The ERGIC is simply a place where they meet up o You don t always find an ERGIC nor is there anything special about what happens there o Eventually vesicles will bud again and continue to the Golgi o The ERGIC is not likely to run into the Golgi by itself for various reasons There are sides to the Golgi cis and trans The correct side to approach is called the cis face The cis means same o The CIS Golgi network is a bunch of separate membrane bound layers o Looks like a stack of pancakes o Vesicles from the ER should approach the front door cis face o The cis face faces the ER o The Golgi is a bunch of separate layers not one large membrane bound organelle o To get from layer to layer you have to bud off more vesicles The Golgi Stack is where most of the processing happens o Lots of enzymes are in the stack o Processing will happen in a sequence across multiple layers in the stack o Therefore it makes sense that enzymes may appear closer to one face than the other o You don t find all of the enzymes in the Golgi in …