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Lecture 6

Lecture 6.docx

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University of Toronto St. George
Jane Mitchell

Ppt25 *Path of transmembrane protein -transmembrane proteins span both the cytosol and ER lumen sides -have a hydrophopic stop sequence, hydrophilic end (cytosol site, interact w aq) -RNA conerted to protein in cytosolic ribosomes, co-translational translocation -signal sequence (N-terminus end) attaches to translocator protein -signal sequence cleaved by signal peptidase -protein is fed into ER until translocator protein reaches stop-transfer sequence -transmembrane protein has different orientation if signal sequence is internal: -can have N-terminus of C-terminus facing cytosol -Determined by AAs around signal sequence -more positive AA side faces cytosol, negative side faces ER lumen *path of multipass transmembrane protein -co-translational tranlocation, N/C-termius both face one side, depends on charge -start and stop sequence both embedded in ER membrane Ppt26 *both star and stop transfers are hydrophobic. *the translocator open laterally and 내보내 the protein *start—is active, targeted to a specific translocator Ppt27 *glycosylated Ppt28 Definition •The Golgi apparatus receives proteins and lipids from the endoplasmic reticulum, modifies them(glycosylation), and then dispatches them to other destinations in the cell by vesicular form. Ppt29 *golgi is a stack of cisterna Protein bud off from ER, fuse w cis golgi, then move through individual cisterna by budding of and fusing to trans cisterna. The reason for this is: glycosylation is complex, it requires several enzymes Ppt30 [Protein Glycosylation] -Actually starts in the ER: A single type of oligosaccharide is attached to many proteins. -Complex oligosaccharide processing required for mature proteins occurs in the Golgi *golgi: multi stage processing unit, different enzymes located at different cisterna -it’s hard to study a specific glycosylation Ppt31 [Maintenance of membrane protein asymmetry] (the direction of proteins ex) toward lumen, toward extracellular) -Each protein is inserted into the membrane in the ER in a specific manner This is the result of ―membrane insertion‖ -This protein asymmetry is maintained through vesicular transport Ppt32 [Recap: Sorting of a PM protein.] •Translation starts on cytosolic ribosomes. •Signal sequence directs the protein to the ER. •There are different ways the protein can be inserted into the membrane. •The signal sequence is: hydrophobic •This is: Co-translational translocation to ER •Protein inserted through the membrane by a: –protein translocator. •Protein moves in transport vesicles to the PM •Vesicle membrane fuses with the PM during Ppt33 *Endosome: membrane-bound organelle that carries materials newly ingested by endocytosis and passes them to lysosomes for degradation. *Lysosome: a small sac of digestive enzymes that functions in degrading worn-out organelles, as well as macromolecules and particles taken into the cell by endocytosis. -endosome and lysosome are temporaly liked doing same function,,BUT can be identified morphologically Ppt35 [Endocytosis] *Endocytosed material found in the early endosome. *Lysosomal proteins are delivered in vesicles from the Golgi -early endosome -late
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