Study Question Sets for Exam 2
Study Question Set 12
Golgi 2

Endocytosis
Corrected 3/20/2006

1. What is the "coat" of the "coated pits" for receptor-mediated endocytosis?
2. Describe the subunit structure of clathrin. Describe a clathrin "cage".
3. Indicate the role(s) of clathrin in receptor-mediated endocytosis.
4. Indicate the role(s) of adaptins.
5. What adaptin is involved in receptor mediated endocytosis?
6. Describe the pH differences between the extracellular fluids and the cell endosome compartments.
7. Describe the sequence of events involved in receptor-mediated endocytosis of ferrotransferrin. (Be complete - include return of the receptors to the cell surface.)
8. Describe the sequence of events involved in receptor-mediated endocytosis of LDLs. (Be complete.)
9. Describe the importance of the pH in the cell endosome compartment, as compared to the cell exterior, for the delivery of the LDL "cargo" to the cell. What differences does one see with cellular uptake of iron by means of transferrin? (Be complete.)
10. Distinguish between "early endosomes" and "late endosomes".
11. What is a multivesicular body?
12. Among early endosomes, late endosomes, and multivesicular bodies, from which can endocytosis receptors be recycled to the plasma membrane?
13. How are excess membrane receptors "down-regulated"? Indicate the role of ubiquitin in the phenomenon.
14. To what compartment do most newly synthesized lysosomal enzymes move when they leave the TGN (trans Golgi network)? How are they directed there?
15. What is responsible for releasing newly synthesized lysosomal proteins from their receptors once they have been delivered from the TGN to the acceptor compartment? Explain briefly. Is this phenomenon unique to lysosomal proteins? Explain briefly.
16. Distinguish between AP1 and AP2 in terms of the membranes at which they function.
17. Compare AP1 vesicles and AP3 vesicles in terms of:
1. The final compartment to which their contents are targeted.
2. The immediate compartments with which the vesicles fuse after leaving the TGN.

Vesicle Traffic

18. Distinguish between the "Regulated Secretory Pathway" and the "Constitutive Secretory Pathway" in eukaryotic cells.
1. Which pathway is considered the "Default Pathway", and why?
2. Indicate the general mechanisms (as we currently understand them) for sorting proteins into the appropriate pathway.
19. Describe in general the 2 major methods of targeting plasma membrane proteins (and lipids) to the appropriate membrane domains in polarized cells other than hepatocytes.
20. Describe in general method of targeting plasma membrane proteins to the apical membrane domain in hepatocytes.   Relate this method to methods seen in other polarized cells.
21. In what plasma membrane domain are lipid rafts generally found in polarized epithelial cells?
22. Describe in general how the components of lipid rafts are targeted to the proper plasma membrane domain.  
23. What is transcytosis? Indicate an important role of transcytosis.
24. What is the vesciular tubular cluster?
25. What is an "ER retention signal"? Explain its role.
1. What is the ER retention sequence in animal cells?
2. In yeast?
3. What are its significant features?
26. How are ER membrane proteins marked for retrieval to the ER from the VTC and the Golgi?
27. How does pH affect the effectiveness of retrieval of "ER resident proteins" from the Golgi?   Explain.
28. What are "COPs"?
29. Contrast the apparent roles of "COP- I vesicles" and "COP- II vesicles" in the early secretory pathway.
30. Explain why the GTP-bound form of sar-1 can participate in the recruitment of COPII proteins to form COPII coated vesicles, but the GDP-bound form cannot.
31. Explain how GTP hydrolysis by sar1 might lead to uncoating of COPII vesicles.
32. Describe the roles of sar-1,   the sec23/24 complex,   and the sec13/31 complex in the formation of COPII coated vesicles.
33. Describe the general structural and functional analogy between clathrin and the relevant COPII component.
34. Distinguish between clathrin coatings and COPs in terms of the sites where they act.
35. Describe the two models for differentiation of different cisternae of the Golgi complex.   Explain the fate of the vesicular tubular cluster in each of these models.   Which model is currently considered more likely to be correct?
36. Explain the general role of Rab GTPases and their associated proteins (effectors and
    guanine nucleotide exchange factors) in docking vesicles to the appropriate target compartment membranes.
37. Describe the GTPase cycle of Rab proteins and relate it to the correct directionality of vesicle transport between compartments.   (I.e., How does the Rab GTPase cycle insure that a vesicle leaving a target compartment to return v-SNARES to the donor compartment does not re-dock with the target compartment instead.)
38. Describe the roles of "v-SNARES" and "t-SNARES" in setting the stage for membrane fusion in the delivery of a vesicle to its target compartment the secretory pathway.
39. Explain how the randomly coiled SNARE protein tails are able to come together and form a "4-helix bundle".
40. Explain how formation of a 4-helix bundle of SNARE protein coils facilitates fusion of a vesicle with the membrane of its target compartment.

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