MCB 130 - Fall 1997 - Burnside - Midterm

MCB 130 - Fall 1997 - Burnside - Midterm - TUE 09:49 FAX...

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Unformatted text preview: 10/17/2000 TUE 09:49 FAX 6434330 MOFFITT LIBRARY 001 MCB 130 MIDTERM Nov. 3, l997 Name________1_._________ Student ID#_ Section day and time Please do not use a pencil for this exam; only pen and ink exams will be graded. Please restrict your answers to the space provided for each question. There are 100 points on the exam and 45—50 minutes to take it. Therefore you have approximately 1/2 minute per point for each question. 1. (12 points) Draw a diagram of the stages of the myosin crossbridge cycle showing the position of the myosin head in relation to the actin filament as it would appear in a myofibril supplied with abundant ATP in the presence of calcium. Then with an arrow and the appropriate letter indicate at which step the cycle would arrest if the myofibril were flooded with a) a non hydrolyzabie ATP analog in the presence of calcium b) a high concentration of inorganic phosphate ions in the presence of calcium 0) an ATP-free medium in the presence of calcium d) a calcium-free medium with a bundant ATP. 2. (12 points; 4 points each) How would you explain the following experimental observations? (Be as specific as possible about underlying processes and emphasize the functional significance of the findings). a. Coichicine does not bind to tubulin subunits in assembled microtubules, yet colchicine treatment leads to microtubule disassembly. b. The ATP-analog vanadate blocks the motility of demembranated flagellar axonemes, retrograde axonai transport, and anaphase A, but does not block anteriorgrade transport or anaphase B. 10/17/2000 TUE 09:49 FAX 6434330 MOFFITT LIBRARY 002 Name p.2 0. When skeletal muscle thick filaments are incubated at high salt concentrations (.5 M), they disassemble into individual myosin molecules; however, the myosin molecules do not disassemble into individual myosin heavy chains. 3. (12 points) How does a focal adhesion differ from a hemidesmosome? Illustrate the components of each to indicate specific differences. Note differences in function. 4. (16 points) a. What is MPF? (name and diagram components) b. How is MPF activity assayed? 0. Name three targets of MPF activity. d. Describe the mechanisms by which MPF is activated and deactivated. Please use diagrams. 10/17/2000 TUE 09:50 FAX 6434330 MOFFITT LIBRARY 003 Name __.___FJ-3 5. (4 points) Suppose you coupled the gene for fimbrin, a non-muscle actin-bundling protein, to a heat shock promoter and tranfected it into cultured fibroblasts. Your transfection was successful, so that when you raised the temperature the cells overexpressed fimbrin. What effects on cell morphology and behavior would you expect to see? 6. (12 points)You have been given a population of cultured cells that have been synchronized with regard to their stage in the cell cycle. You divide the population into three culture dishes. When all the cells are in the G2 phase of the cycle, you add cytochalasin to one dish, colchicine to another dish and leave one dish untreated to serve as a control. After six hours, you remove all the cells from their dishes and put them through a cell sorter to analyze the mass of DNA in each cell. You find that the cytochalasin- and the colchicine-treated cells have twice as much DNA per cell as the control cells. a)Why? b) What difference(s) might you expect to find in the way that the DNA is organized in the cells after the three treatments? Y. (9 points total; 3 points each) Describe the functional significance of the following structures or molecules (is. describe what they do and what they interact with, and why this is important to the cell): a. centromeres b. tropomodulins c. nexin linkers 10/17/2000 TUE 09:50 FAX 6434330 MOFFITT LIBRARY 004 Name p.4 8. (24 points total; 4 points each) Describe the functional significance of the following processes or events (is. describe what happens to what cell components and why this is important to the cell): a. GTP hydrolysis by beta-tubulin b. cytochalasin binding to actin filaments c. cleavage of propeptides from procollagen d. phosphorylation of nuclear lamins e. secretion of hyaluronidase by pathogenic bacteria f. calcium binding to cadherins ...
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MCB 130 - Fall 1997 - Burnside - Midterm - TUE 09:49 FAX...

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