Biol110-10-FINAL EXAM-KEY1

Biol110-10-FINAL EXAM-KEY1 - B io l1 1 0 1 0 F in a l E x a...

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Biol110-10-Final Exam Name __Michael_____ ___Rexach____ Exam # __0__ Biol110 Cell Biology Fall 2010 Final Exam Tuesday, December 7, 2010 Instructions: Use pen or pencil. Write your NAME and EXAM NUMBER in every page. Be brief in each answer, but write full sentences; include key words and mechanistic detail Each question is worth 25 points, assigned as indicated. Use only the backside of the question page for extra writing space, if needed. This is a closed book & notebook exam. Grading: Question #1 ___25___ Question #2 ___25___ Question #3 ___25___ Question #4 ___25___ Total Score __100____ Letter Grade __A+____
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Biol110-10-Final Exam Name __Michael_____ ___Rexach____ Exam # __0__ Question #1: Vesicular traffic and the late secretory pathway What are three main functions of protein coat in vesicular trafficking within cells? (3 pts) How are specific sites for transport vesicle assembly on membranes selected? (2 pts) Protein coats are used to: (i) deform flat membranes into curved membranes to form a vesicle (1 pt); (ii) selectively capture proteins and phospholipds as vesicle cargo (1 pt); and (iii) to prevent premature fusion of a vesicle with its target membrane (by masking the vSNARE in the vesicle surface) (1 pt). The sites for vesicle assembly are selected by guanine exchange factors (GEF) (1 pt) that act on the small GTPases that function as coat proteins such as Sar1 and Arf1 (1 pt). Upon binding GTP, these monotopic membrane proteins recruit other coat proteins to the site (1 pt). In reconstituted ER-to-Golgi vesicular traffic, why was addition of transport inhibitor(s) required in order to purify transport vesicles? (1 pt) What two inhibitor(s) yielded vesicles suitable for purification and why? (4 pts) Inhibitors were required because ER-to-Golgi transport vesicles do not normally accumulate; they are only transient intermediates in a pathway (1 pt) A mutation in the small Rab protein Ypt1 (1 pt) yielded suitable vesicles because it prevented their docking to cis-Golgi membranes, possibly by interfering with the Rab-tetherin interaction (1 pt) or by preventing the unmasking of the tSNARE (1 pt). The non-hydrolyzable analog of GTP (GTP γ S or GMP-PMP) (1 pt) also produced suitable vesicles because it blocked the GTP hydrolysis-dependent disassembly of the coat, which is a pre- requisite for docking to the cis-Golgi (1 pt). Do proteins destined for the plasma membrane leave the trans-Golgi membrane by bulk flow? Explain. (2 pts) How is the fusion of synaptic vesicles regulated at the synapse, and what signaling-cascade triggers the fusion event? (3 pts) Some proteins do leave the trans-Golgi membrane by bulk flow inside vesicles (1 pt), while others are specifically selected at the trans-Golgi membrane for incorporation into clathrin-coated vesicles destined for early endosomes (1 pt) or into regulated vesicles destined for the plasma membrane (1 pt). The fusion of synaptic vesicles is regulated by a ‘calcium clamp’, which is imposed by
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Biol110-10-FINAL EXAM-KEY1 - B io l1 1 0 1 0 F in a l E x a...

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