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Unformatted text preview: BIS104 Winter 2012 Problem Set 4 1. You briefly (about 15 minutes) label tissue culture cells with radioactive H 3 thymidine. You then look at time points at later times. At each time point, you collect the cells in mitosis and quantitate the percentage of cells that are labeled with radioactive thymidine (see the graph). What is the length of G2 in these cells? About 10 hours (9-12 hours is a good answer). Thats how long it takes for the last cell in S phase (which was labeled with H3 thymidine) to become the first cell in mitosis (how long it took for any cells in mitosis to be labeled with H3 thymidine). 2-5. You have microinjected a newt lung cell with rhodamine-labeled tubulin, c aged- fluorescein labeled tubulin and the fluorescent DNA stain, DAPI. You wait until the cell enters metaphase and you uncage a bar of caged-fluorescein tubulin in the spindle. The figures below show the fluorecence intensity of uncaged fluorescein on the y axis and the distance from the left spindle pole (centrosome) on the x axis. The position of one sister chromatid that is attached to the left pole by a kinetochore fiber is also shown. 3 6 9 12 15 18 21 24 27 30 33 35 Time in hours after H 3 thymidine pulse %ofM- phasecellsthatare labeledwithH 3 Thymidine 2. What is the rate of poleward flux in m min-1 ? 0.5 m/min 3. What is taxol, and what will happen to the rate of poleward flux and the movement of chromosomes in the presence of taxol? be affected by the addition of taxol? Taxol will stabilze microtubules and inhibit depolymerization. Since poleward flux requires loss of tubulin subunits at the minus end of the microtubule, poleward flux will be inhibited by taxol and the chromosomes will not move towards the poles. will be inhibited by taxol and the chromosomes will not move towards the poles....
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- Winter '08