midterm_w05KEY - 1 BIS 104 Section 2 MIDTERM February 8...

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1 BIS 104 - Section 2 MIDTERM February 8, 2005 1. (5) You are working on coated vesicles that transport cargo through the cytosol. When you add a non hydrolysable form of GTP you notice that the coated vesicles start to accumulate in the cells. a. What type of transport vesicles are these and where are they coming from? ________________________ COPI (from Golgi), COPII (from ER), CLATHRIN (from TGN). b. Why are these coated vesicles accumulating in the treated cells? Because the GTPases associated with the coat are unable to hydrolyze GTP so that the coat remains associated with the vesicles. Since vesicles are not being uncoated they accumulate in the cells. c. At the same time you notice that transport of proteins into the nucleus is stopped. Which protein that is part of the nuclear transport machinery do you predict will be affected? _________ Will the ability of the nuclear import receptor to recognize the NLS be affected? ___________ Why or why not? Ran will be affected. When the RanGTP is not hydrolyzed to Ran GDP the Ran stays associated with the import receptor so that it is not free in the cytosol and does not bind the NLS. 2. (2) You are studying a patient who has dense abnormal looking lysosomes. Previous tests on this patient has indicated that she has a mutation in the enzyme, N-acetylglucosamine phosphotransferase that is required for adding phosophate groups to mannose residues. Why would lack of this enzyme, normally found in the Golgi, cause a lysosomal problem? The lack of Man-6-P label means that the lysosomal acid hydrolyases will not be targeted to the lysosome (or will remain in the TGN). Without hydrolases in the lysosome the material brought into the lysosome will not be properly degraded. 3. (4) A cytosolic chaperone belonging to the hsp70 family is required for import of proteins into the mitochondria. a. Why is it necessary? __________________ b. Is a similar chaperone required for import into the nucleus? __________ Depending on your answer explain why you think it is or is not needed? The cytosolic chaperone keeps the protein for import into the mitochondria unfolded so it can thread its way through the TOM and TIM. Folded proteins can enter the nucleus because of the size of the nuclear pores and therefore this chaperone is not needed for this import process.
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2 4. (7) You are following the path of a red fluorescent LDL receptor at the same time you are following the path of the EGF receptor that is tagged with a green fluorescent dye. In some intracellular compartments you find both receptors. a. Name one compartment where you expect to find both receptors. __________________ Describe all the steps that got both receptors to this compartment. Both receptors will be taken up into clathrin coated pits that will pinch off to form clathrin
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midterm_w05KEY - 1 BIS 104 Section 2 MIDTERM February 8...

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