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26 Cards in this Set
- Front
- Back
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What is Bip?
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An ER resident protein. A type of chaperone that folds extracellular domains of transmembrane proteins
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What is Anti-Bip?
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An antibody that binds to bip
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What was the experiment that showed where Bip was found in cell?
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Conjugated gold to Anti-Bip, then could see it in ER, vesicles going to cis golgi, a little in cis+med golgi, none in trans golgi.
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What is a retension signal?
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Signals to protein, don't leave!
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What is a retrieval signal?
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Signals to protein, come back!
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What is the nature of the ER signal to keep it's proteins? How do we know?
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Retrieval. Otherwise we wouldn't see it in the golgi at all (it would all stay in ER, or get secreted if it somehow accidentally escaped)
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What happens if Bip is way over expressed in the cell? (as an experiment)
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Bip gets released. It can overwhelm the retrieval signal.
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What is the ER retrieval signal?
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Just four amino acids at end of C terminus of every ER resident protein: (N terminus)---------KDEL (C terminus)
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What does the KDEL receptor look like?
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N terminus: (KDEL binding, inside ER lumen) --------[hydrophobic transmembrane domain]------KKXX (COPI binding, cytoplasm) : C terminus
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How does ER retrieval work?
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KDEL receptor only binds to ---KDEL sequence when in golgi! Then the --KKXX on the cytoplasm side recruits COPI, and retrograde transfers back to ER
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What do vesicle "coats" do?
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1. Help pinch off a vesicle, 2. Help direct vesicles to target
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Which coat protein mediates retrograde traffic?
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COPI
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Which coat protein mediates anterograde traffic?
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COPII
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Which coat protein targets the lysosomal pathway?
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Clathrin
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What are the two models of golgi function? What do you expect to see on/in side vesicles? Which has the most supporting evidence?
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1. **Cisternal maturation/progression model**: Like an escalator. Vesicles move backward, coated in COPI, contain golgi enzymes. 2. Stationary cisternae model: Like a staircase. Vesicles move forward, coated in COPII, contain secretory proteins. (cisternal maturation is best model)
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What does clathrin look like?
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3 heavy chains, 3 light chains, spontaneously forms multimers (pentagons and hexagons)
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What does clathrin do?
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1. Associates with the cellular membrane to drive vesicle budding. 2. Targets vesicles to the endosome which become the lysosome.
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Where is clathrin found?
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at the plasma membrane, at the gogli nework
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Example of protein to which clathrin binds?
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the cellular side of the M6P receptor (remember acid hydrolases that need to get to lysosome)
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How does endocytosis work?
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1. Initial invagination of membrane by clathrin. 2. Recruitment of dynamin (like a molecular noose) 3. Hydrolysis of 1 GTP/dynamin monomer tightens noose until vesicle pops off.
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How does exocytosis work?
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1. V-snares on vesicle bind with T-snares on membrane. 2. Hydrolysis of ATP twists "ropes" of V and T snare. 3. Membranes fuse
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What are the three forms of endocytosis?
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1. Pintocytosis (cellular drinking), 2. Phagocytosis (cellular eating), 3. Receptor mediated endocytosis
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Explain Pintocytosis
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Cellular drinking, non-specific uptake, can't see what's in vesicles
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Explain Phagocytosis
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Cellular eating, non-specific uptake, larger things in vesicles
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Explain Receptor mediated endocytosis
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1. Receptor proteins (transmembrane at cell surface) bind to an extracellular ligand. 2. The cytoplasmic side of the receptor protein binds clathrin. 3. Targets endosome -> late endosome -> lysosome (drastic decrease in pH)
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What three things can happen to an endocytosed vesicle?
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1. Transcytosis (cross cell intact) 2. Mutual degradation (both ligand and receptor destroyed in lysosome) 3. Ligand degradation (ligand to lysosome, but receptor recycled to cell surface).
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