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\- In what ways is eukaryotic replication similar to bacterial replication, and in what ways is it different?

Phosphorus is required to synthesize the deoxyribonucleoside triphosphates used in DNA replication. A geneticist grows some \(E .\) coli in a medium containing nonradioactive phosphorus for many generations. A sample of the bacteria is then transferred to a medium that contains a radioactive isotope of phosphorus \(\left(^{32} \mathrm{P}\right) .\) Samples of the bacteria are removed immediately after the transfer and after one and two rounds of replication. Assume that newly synthesized DNA contains \(^{32} \mathrm{p}\) and the original DNA contains nonradioactive phosphorus. What will be the distribution of radioactivity in the DNA of the bacteria in each sample? Will radioactivity be detected in neither, one, or both strands of the DNA?

DNA topoisomerases play important roles in DNA replication and in supercoiling (see Chapter 11 ). These enzymes are also the targets for certain anticancer drugs (see the introduction to this chapter). Eric Nelson and his colleagues studied m-AMSA, one of the anticancer compounds that acts on topoisomerase (E. M. Nelson, K. M. Tewey, and L. F. Liu. \(1984 .\) Proceedings of the National Academy of Sciences of the United States of America 81:1361-1365). They found that m-AMSA stabilizes an intermediate produced in the course of topoisomerase action. The intermediate consists of topoisomerase bound to the broken ends of the DNA. Breaks in DNA that are produced by anticancer compounds such as m-AMSA inhibit the replication of the cellular DNA and thus stop cancer cells from proliferating. Explain how m-AMSA and other anticancer agents that target topoisomerase enzymes taking part in replication might lead to DNA breaks and chromosome rearrangements.