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Unformatted text preview: BIS 104, Section 2, Winter quarter 2011 Answers, Assignment 2 Answers are in red beneath each question. 1) A rapidly growing yeast culture was pulsed for two minutes with 3 H-leucine and then washed and chased with medium containing unlabeled leucine. At various time intervals after the beginning of the chase, aliquots were removed from this culture and fractionated as follows: (A) The cells were separated from the cell medium by low speed centrifugation. (B) The cell pellet from step (A) was washed with buffer and then disrupted by sonication in the presence of sucrose. (C) The homogenate from step (B) was subjected to preparative ultracentrifugation in dilute sucrose at a speed and time sufficient to pellet all of the organelles. (D) The organelles in the pellet from step (C) were separated from one another by sedimentation equilibrium in a sucrose density gradient. Each of the above fractions was treated with detergent and then combined with antibodies against carboxypeptidase Y, a vacuolar yeast protein. The immunoprecipitates from each fraction were counted in a gamma counter and the cpm obtained for the immunoprecipitates from each fraction at each time interval are listed in the table below. Chase time Cell Fraction 5 min 10 min 15 min 25 min Cell medium 0 0 0 0 Golgi 100 22,000 2,114 53 Microsomes 24,800 100 27 0 Mitochondria 0 0 0 0 Vacuoles...
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- Winter '08