Exam 3: RR (7)

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Exam 3: RR (7)
2013-11-09 09:06:41
Cell Bio

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  1. a.      biosynthetic pathway consists of series of membrane-bound organelles that function in the __
                                                                  i.      materials are carried by __ from __ to __
    • ssynthesis, modification, and delivery of soluble and membrane proteins to their appropriate destination in the cell
    • budding vesicles
    • donor membrane
    • acceptor membrane
  2. 1.      most vesicles covered by “__ dense layer= protein coat formed from __ that assemble on the __ of the donor membrane at sites where budding takes place
    a.      each coated bud pinches off to form a __
                                                                                                                                          i.      similar size and structure that are formed in __
    • fuzzy” electron
    • soluble proteins
    • cytosolic surface
    • coated vesicle
    • cell-free systems
  3. a.      protein coat functions
    •                                                               i.      mechanical device that causes the membrane to curve and form a budding vesicle
    •                                                             ii.      they provide a mechanism for selecting the components to be carried by the vesicle
  4. 1.      selected components include
    a.      cargo consisting of __, __, and __ to be transported
    b.      machinery required to __ and __ to the correct acceptor membrane
    • secretory, lysosomal, and membrane proteins
    • target and dock the vesicle
  5.                                                               i.      the vesicle coat is composed of two distinct protein layers: ____

    an outer cage or scaffolding that forms the framework for the coat and an inner layer of adaptors that binds both to the outer surface of the lipid bilayer and the membrane’s cargo
  6. 1.      the adaptors select specific cargo molecules by virtue of their specific affinity for the __that reside in the donor membrane
    cytosolic “tails” of integral proteins
  7. a.      Classes of coated vesicles distinguished by the proteins that make up their coat, their appearance in EM, and their role in cell trafficking, The three are:
    • COPII-coated vesicles
    • COPI-coated vesicles
    • Clathrin-coated vesicles
  8. COPII-coated vesicles do what?
    move materials from the ER “forward” to the ERGIC and Golgi complex
  9. COPI-coated vesicles
    move materials in a retrograde direction from the ERGIC and Golgi stack “backward” toward the ER and from trans Golgi cisternae “backward” to cis Golgi cisternae
  10. Clathrin-coated vesicles
    •                                                               i.      move materials from the TGN to endosomes, lysosomes, and plant vacuoles
    • 1.      they move materials from the plasma membrane to cytoplasmic compartments along the endocytic pathway and have been implicated in trafficking from endosomes and lysosomes
  11. a.      COPII-Coated Vesicles and Transport
                                                                  i.      COPII-coated vesicles mediate the __ through the biosnyhtetic pathway—from the __
                                                                ii.      The __ contains a number of proteins that were first identified in mutant yeast cells that were unable to carry out transport from the ER to the Golgi complex
    first leg of the journey

    • ER to the ERGIC and Golgi complex                                                           
    •  COPII coat
  12.                                                               i.      homologues of the yeast proteins were found in the coats of vesicles budding from the ER in mammalian cells
    __ to __ block __ from ER membranes but have no effect on __ at other stages in the secretory pathway
    • antibodies to COPII-coat proteins
    • budding of vesicles
    • movement of cargo
  13.                                                               i.      __ select and concentrate certain components for __
    1.      certain integral membrane proteins of the ER are __ because they contain__ as part of hteir __
    a.      these signals interact specifically with __ of the vesicle coat
    • COPII coats
    • transport in vesicles
    • selectively captured
    •  “ER export” signals
    • cytosolic tail
    • COPII proteins
  14. 1.      proteins selected by COPII-coated vesilcees include: (1-2)
    • a.      enzymes that act at later stages in the biosynthetic pathway, like the glycosyltransferases of the Golgi complex
    • b.      membrane proteins involved in the docking and fusion of the vesicle with the target compartment
  15. 1.      proteins selected by COPII-coated vesilcees include: (3)
    a.      membrane proteins that are able to bind soluble cargo (such as the secretory proteins)
  16.                                                                                                                                       i.      cells lacking a specific cargo receptor typically fail to do what?
    transport a specific subset of proteins from the ER to the Golgi complex
  17. 1.      Among the COPII coat proteins is a __, which is recruited specifically to the ER membrane
    a.      like other G proteins, __plays a __role, in this case, by __ and by __
    • small G protein called Sar1
    • Sar1 
    • regulatory 
    • initiating vesicle formation
    • regulating the assembly of the vesicle coat
  18. Example steps:

    1.      __recruited to ER membrane in the __ form and is induced to exchange its __for a molecule of __
    2.      upon binding, __undergoes a conformational change that causes its__ to insert itself into the __ of the ER bilayerà does what to the lipid bilayer, aided by a change in __
    • Sar1 
    • GDP-bound
    • GDP 
    • GTP

    • Sar1 
    • N-terminal alpha helix
    • cytosolic leaflet
    • bends 
    • packing of the lipids that make up the two leaflets of the bilayer
  19. Example steps:

    1.      __ recruited two additional polypeptides of the COPII coat, which bind as a banana- shaped dimer
    a.      curved shape provides __ on the membrane surface to help it do what?
    2.      the remaining subunits of the __ bind to the membrane to form the outer structural cage of the protein coat
    • Sar1-GTP
    • additional pressure
    • further bend into a curved bud
    • COPII coat

  20. 1.      Once the entire COPII coat has assembled, the bud is __ in the form of a __. Before the coated vesicle can fuse with a target membrane, the protein coat must be __and its components __
    • separated from the ER membrane
    • COPII-coated vesicle
    • disassembled 
    • released into the cytosol
  21. a.      disassembly is triggered by __ to produce a __ subunit, which has decreased affinity for the vesicle membrane
    2.      dissociation of __ from the membrane is followed by the releases of the other __subunits
    • hydrolysis of the bound GTP
    • Sar1-GDP
    • Sar1-GDP
    • COPII
  22. a.      Transporting Escaped Proteins Back to the ER
                                                                  i.      __ were first identified in experiments in which cells were treated with molecules similar in structure to GTP but, unlike GTP, can’t be hydrolyzed
    1.      under these conditions, __ accumulated within the cell and could be isolataed from homogenized cells by __
    • COPI-coated vesicles
    • COPI-coated vesilces
    • density gradient centrifugation
  23.                                                               i.      COPI-coated vesicles accumulate in the presence of a non-hydrolyzable GTP analogue because, similar to their COPII counterparts, what?
    the coat contains a small membrane bending GTP binding protein called AFR1, whose bound GTP must be hydrolyzed before the coat can disassemble 
  24.                                                               i.      COPI-coated vesicles have been most clearly implicated in the retrograde transport of proteins, including the movement of __ and __
    • 1. Golgi resident enzymes in a trans-to-cis direction 
    • 2. ER resident enzymes from the eRGIC and the Golgi complex back to the ER
  25. a.      Retaining and Retrieving Resident ER Proteins
                                                                  i.      Proteins are maintained in an organelle by a combination of two mechanisms
    1.      __
    a.      __ may be based primarily on the physical properties of the protein
    2.      __
    retention of resident molecels that are excluded from transport vesicles

    • retention
    • retrieval of escaped molecules back to the compartment in which they normally reside
  26.                                                               i.      proteins that normally reside in the ER, in both the lumen and in the membrane, contain __ at their __that serve as __, ensuring their return to the ER if they should be accidentally carried forward to the __ or __
    1.      the retrieval of “escaped” ER proteins from these compartments is accomplished by __that __ and __
    • short amino acid sequences
    • C-terminus 
    • retrieval signals
    • ERGIC or Golgi complex
    • specific receptors 
    • capture the molecules
    • return them to the ER in COPI-coated vesicles
  27.                                                               i.      soluble resident proteins of the ER lumen typically possess the retrieval signal “__”
    1.      these proteins are recognized and returned to the ER by the __, an integral membrane protein that shuttles between the cis Golgi and the ER compartments
    • lys-asp-glu-leu
    • KDEL receptor
  28. 1.      if the __ is deleted from an ER protein, the escaped proteins are not returned to the ER but instead are carried forward through the Golgi complex
    KDEL sequence
  29.                                                               i.      Conversely, when a cell is genetically engineered to express a __ or __ protein that contains an added __, that protein is returned to the __rather than being sent on to its proper destination
                                                                ii.      Membrane proteins that reside in the __also have a __ that binds to the __, facilitating their return to the ER
    1.      the most common retrieval sequences for ER membrane proteins involve two closely linked __, most commonly KKXX
    • lysosomal or secretory
    • KDEL C-terminus
    • ER 
    • ER 
    • retrieval signal
    • COPI coat
    • basic residues
  30.                                                               i.      Each membrane compartment in the __ may have its own __signals, which helps explain how each compartment can maintain its unique complement  of proteins despite the constant movement of vesicles in and out of that compartment
    • biosynthetic pathway
    • retrieval