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bio 320 exam 3 answer key

bio 320 exam 3 answer key - BIO 320 Dr Bushart Midterm...

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BIO 320 Dr. Bushart Print Name:___________________________ Midterm Exam #3 10 AM Friday August 15, 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. The short-answer 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. 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). Short answer (100 points): There are 9 short-answer questions. 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. (12 points) Neurons extend their axons through structures called growth cones. The movement of a growth cone is much like that of a crawling keratocyte, but a tube of membrane and cytoplasm (the axon) is left behind the crawling tip. a. (4 points) What step(s) of crawling locomotion does a growth cone have in common with a keratocyte? Which step(s) and components might be unnecessary? Explain. A growth cone would need to undergo protrusion for forward extension of the cytoplasm. It would also need to have attachment to the underlying substrate for anchoring and a point of further extension. Since the trailing nerve body is left behind, however, it would not be undergoing traction and so may not need myosin. b. (6 points) Keeping a migrating growth cone on track appears to function through inhibiting locomotion occurring in incorrect directions. Off-track explorations experience “growth cone collapse.” Integrins are known to play a role in this process. Assume for this question that integrins strongly bound to the internal cytoskeleton will in turn signal for the stabilization of the cytoskeleton. In what two ways could external inhibition of integrins prevent forward migration of the growth cone? First, simple inhibition of external binding is going to interfere with the attachment step of forward movement. The second factor is that inhibiting the binding ability of the external portion of integrin is in turn going to weaken the internal binding of integrin to the cytoskeletal network (actin most likely). If proper binding stabilizes the cytoskeleton, then lack of proper binding should allow for its disassembly (the collapse).
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