view.php?id 1551586 University of Cincinnati CHEM 3040 Spring 15 MERINO: Chp 4 H
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view.php?id 1551586 University of Cincinnati CHEM 3040 Spring 15 MERINO: Chp 4 HW Reade O mod biscm Deb Map sapling learning In a famous experiment, Matthew Meselson and Franklin Stahl grew E. coli cells in a medium containing only the "heavy" isotope of nitrogen, 15N. These cells were then transferred to a medium with the "light" isotope of nitrogen, 14 The results of the experiment supported the hypothesis of semiconservative replication, which was proposed by Watson and Crick. a) Heavy DNA (5N DNA), hybrid DNA, and light DNA (4N DNA) can be separated by centrifugation. cells containing 15N DNA are transferred to a medium with only "N NH4CI as a nitrogen source, what percent of daughter molecules are composed of hybrid DNA after 4 generations? Number b) Predict what percent of daughter molecules would be composed of hybrid DNA if DNA exhibited conservative replication -that is, if a daughter DNA molecule were composed of newly synthesized DNA only. NumberExplanation / Answer
a)
In the experiment conducted by Meselson and Stahl, semiconservative replication is resulted containing 1 strand of 15N DNA and 1 strand of 14N DNA. This means 50%of 15N DNA and 50% of 14N DNA. This is resulted in 2nd generation. In fourth generation 25% 15N DNA, 50% of 15N and 14N hybrid DNA and 25% of 14N DNA are resulted. This is because each time of replication in semiconservative type one old strand is retained and a new strand is synthesized.
b)
In conservative replication completely 2 new strands are synthesized. Hence, the hybrid DNA resulted would be 25% and 50% of 14N DNA and 25%of 15N DNA.
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