320Fall08Midterm1_v3_Key

320Fall08Midterm1_v3_Key - BIO320Dr.Bushart MidtermExam#1...

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BIO 320 Dr. Bushart Print Name:__________Key______________ Midterm Exam #1 Thursday September 18, 2008 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. Write a clear concise answer for each question. Some questions may have more than one possible answer but require you to defend your choice. The questions have specific 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 drawing as part of your answer, be sure to also include appropriate labeling and/or a short written explanation. . This exam is comprised of 9 short-answer questions worth a total of 100 points (the points for each section/ question are noted in parentheses). To receive full credit you must clearly and fully answer the question being asked. Partial credit may be given in 0.5 point increments. Be sure you include clear explanations in your response. Make sure your response answers the question being asked! 1. (10 points) CO 2 is nonpolar. a. (4) Why does CO 2 (as written) not need transport proteins to enter the cell? CO 2 is small and nonpolar. Small and nonpolar molecules can diffuse through the hydrophobic core of a lipid bilayer and so can freely enter a cell. b. (6) CO 2 achieves greater effective solubility in water by forming carbonate, as described by the reaction: H 2 O + CO 2 HCO 3 + H + . Why then do red blood cells (RBCs) require transport proteins (like Band 3) to aid in delivery of total CO 2 to the lungs? HCO3 is an ion and ions will not cross a lipid bilayer since they cannot pass through the hydrophobic core. Therefore a transport protein is needed to move the carbonate even if the CO 2 can diffuse on its own. [Waiting for the carbonate to transition back to carbon dioxide would be too slow.] 2. (10 points) CFTR is an anion channel that mostly transports Cl - ions and is mutated in the most common form of cystic fibrosis. In cystic fibrosis, Na + concentrations are known to be altered. However, this is probably due to secondary effects on Na + -specific transporters and not due to Na + being transported by CFTR itself. Using what you know about the selectivity of channels for ions, explain why it is unlikely that a single mutation in CFTR would allow for Na + to flow through CFTR. Ion channel selectivity depends on several factors. The key to this is that we are looking at the possibility of an anion channel suddenly transporting a cation. It is very unlikely that a single mutation would reverse all the possible selection mechanisms (surface charges, pore helices, selectivity filters, etc.) to allow an oppositely charged ion through.
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3. (12 points total) Mutations that lead to changes in the amino acid sequence (primary sequence) of proteins have the potential to impact their function. a.
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This note was uploaded on 02/18/2010 for the course BIOLOGY 320 taught by Professor Saxena during the Spring '10 term at University of Texas.

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320Fall08Midterm1_v3_Key - BIO320Dr.Bushart MidtermExam#1...

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