BIO 320 2009 Fall Exam 3 Key

BIO 320 2009 Fall Exam 3 Key - BIO 320 Dr. Bushart Print...

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BIO 320 Dr. Bushart Print Name:__________Key_________________ Midterm Exam #3 2 PM Thursday November 5, 2009 General instructions: Read each question carefully and don’t hesitate to ask if a question seems unclear. Trying to provide an answer for every question is advantageous; you will not be penalized for guesses. The short-answer questions have speciFc answers, although for some, more than one answer is possible. If possible, answer each question in the space provided, but if needed, continue on the back. If you use a diagram as part of your answer, be sure to also include appropriate labeling and/or a short written explanation. To receive full credit you must clearly and fully answer the question being asked. Partial credit may be given in 0.5 point increments. This exam is worth 100 points (the points for each section/question are noted in parentheses). Use pen if you want a chance for a regrade. Short answer: There are 8 short-answer questions over 3 pages. Write a clear concise answer for each question. Some questions may have more than one possible answer but require you to defend your choice. Be sure you include clear explanations. Make sure your response answers the question being asked! 1. (8 points) Explain in terms of the Signal Recognition Particle (SRP) why replacing a protein’s ER signal sequence with a “generic” transmembrane α -helix region would not have an effect on the import of the protein. The SRP recognizes hydrophobic sequences via its hydrophobic binding pocket (which is lined with methionines, but that doesn’t have to be mentioned). A transmembrane alpha- helix would, by necessity, also be composed of hydrophobic amino acids. Therefore any region that can function as a transmembrane alpha-helix can also be recognized by the SRP as an ER signal sequence. 2. (9 points) Chaperone-like proteins are necessary to recycle SNARE and clathrin proteins for reuse. Explain why this makes sense in terms of the energetics and functions of these proteins. Both SNAREs and clathrin proteins work by strong associations with other units (v- to t- SNARES; clathrin “legs” to other clathrin legs). These associations are highly favorable in terms of energy (strongly exergonic, large negative deltaG) because they are used to shape membranes in ways that are unfavorable (pushing them together in the case of SNARES, bending them in the case of clathrin). Because these associations are stable it takes the involvement of a chaperone-like protein to use ATP to pry them apart so that they can be used again. Information in parenthesis is optional for full credit. 3.
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BIO 320 2009 Fall Exam 3 Key - BIO 320 Dr. Bushart Print...

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