341lecture26nov13sakai

341lecture26nov13sakai - Cell Biology 341 Friday, November...

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Cell Biology 341 Friday, November 13, 2009 Today: • Types of vesicle coats • Regulation of vesicle traffic in the secretory pathway • Sorting from the Golgi apparatus Last lecture: concluded chapter 12 • 2 additional types of single-span membrane proteins each contain a single internal start- transfer sequence; the + charge near this signal sequence determines whether the N- terminal or the C-terminal is in the cytosol • Multipass proteins contain pairs of internal start-transfer sequences and stop-transfer sequences • Answers to questions at the end of chapter 12 are posted on Sakai; see #16 and others I listed • Also see the videos on protein sorting for chapter 12 on your DVD sequences • Began Chapter 13: all proteins directed to the ER (secretory pathway) contain a signal recognized by the SRP, either an N-terminal cleaved signal or a start transfer sequence (not cleaved) • If only an SRP-recognized ER signal: protein will be secreted or located in the plasma membrane • Proteins travel by vesicles in the secretory pathway and during endocytosis
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The secretory pathway begins in the ER • Polypeptides are folded and assembled into multi-subunit proteins in the lumen of the endoplasmic reticulum • Glycosylation (addition of oligosaccharides glycoprotein) and formation of disulfide bonds take place in the ER as the protein enters the lumen • The oligosaccharide chains are chemically modified in the ER and Golgi apparatus by enzymes located specifically in each compartment • Only proteins that are properly folded and assembled (ex: antibodies) are allowed to leave the ER in vesicles • Proteins selected to leave the ER may contain unknown exit signals; most proteins appear to leave the ER without the help of a signal
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Glycoproteins are processed in the Golgi apparatus Cis face is next to ER, toward nucleus Trans face is toward plasma
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341lecture26nov13sakai - Cell Biology 341 Friday, November...

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