Cisternal maturation model

Cisternal maturation model - N linked- sugars attached to...

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N linked- sugars attached to asparganine (RER and Golgi) Olinked- sugars attached to serine or threonine (Golgi) During synthesis on rER Transfer of a chain of sugars to the nascent protein Donor: Dolichol pyrophosphate Sugar chain trimmed while in ER Further modifcations in Golgi Sugar Modifications in Lysosomal enzymes: Packaging and Directing Phosphorylation of mannose on lysosomal protein precursors. Lysosomal follow secretory pathway. Hurlers??!! Cisternal maturation model : the cisternae of the Golgi apparatus move by being built at the cis face and destroyed at the trans face. Vesicles from the endoplasmic reticulum fuse with each other to form a cisterna at the cis face, consequently this cisterna would appear to move through the Golgi stack when a new cisterna is formed at the cis face. This model is supported by the fact that structures larger than the transport vesicles, such as collagen rods, were observed microscopically to progress through the Golgi apparatus. Recently it has made a comeback, as laboratories at the University of Chicago and the University of Tokyo have been able to use new technology to directly observe Golgi compartments maturing. [7] . Additional evidence comes from the fact that COP1 vesicles move in the retrograde direction, transporting ER proteins back to where they belong by recognizing a signal peptide
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Frozen sections treated with antibodies were linked to gold particles. According to this model, Golgi cisternae in a stack have differing identities. Coated Vesicles COPII move materials from the ER forward to the ERGIC and the Golgi complex. COP I coated vesicles moves materials retrograde from the ERGIC and golgi backward toward the ER, and from the trans cisternae to the cis cisternae. Clathrin coated vesicles move materials from the TGN to endosomes, lysosomes,a nd plant vacuoles. They also move materials from the plasma membrane to cytoplasmic compartments along the endocytic pathway. Implicated in trafficking form endosomes and lysosomes. COP1 Coated Vesicles, escaped proteins back to the ER. First identified in cells treated with GTP analogues, so COP1 vesicles accumulated and could be isolated with centrifugation. . Protein coat contains ARF1, whose bound GTP must be hydrolyzed before the coat can disassemble. COP1 mediates retrograde transport of proteins, movement of proteins in a trans to cis direction, and moving ER rReident enzymes from the ERGIC and Golgi back to the ER. Proteins that normally reside in the ER have a short C terminal signal “retrieval signal” ensuring return to ER. Soluble resident proteins of the ER lumen typically contain retrieval signal “lys- asp-glu-leu” or KDEL. These proteins are recognized and returned to the ER by the KDEL
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receptor, an integral membrane protein that shuttles nbetween the cis Golgi and ER compartments. If the KDEL signal is delted the escaped proteins are carried through the Golgi. Conversely, engineering a protein to have its signal when it shouldn’t causes it to not go where it
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This note was uploaded on 04/21/2008 for the course BSCI 330 taught by Professor Payne during the Spring '08 term at Maryland.

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Cisternal maturation model - N linked- sugars attached to...

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