1. Discuss different models for DNA replication that were considered by early researchers. Explain why the...

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Biology

1. Discuss different models for DNA replication that wereconsidered by early researchers. Explain why the current model forDNA replication was accepted following experiments by Meselson andStahl. Describe this model in detail and interpret the significanceof helicases, gyrases, RNA primer, DNA polymerase, Okazakifragments, and DNA ligase.

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There were three models of replication possible from such a scheme conservative semiconservative and dispersive In conservative replication the two original DNA strands known as the parental strands would rebasepair with each other after being used as templates to synthesize new strands and the two newlysynthesized strands known as the daughter strands would also basepair with each other one of the two DNA molecules after replication would be allold and the other would be allnew In semiconservative replication each of the two parental DNA strands would act as a template for new DNA strands to be synthesized but after replication each parental DNA strand would basepair with the complementary newlysynthesized strand just synthesized and both doublestranded DNAs would include one parental or old strand and one daughter or new strand In dispersive replication after replication both copies of the new DNAs would somehow have alternating segments of parental DNA and newlysynthesized DNA on each of their two strands Meselson and Stahl Meselson and Stahl were interested in understanding how DNA replicates They grew E coli for several generations in a medium containing a heavy isotope of nitrogen 15N that is incorporated into nitrogenous bases and eventually into the DNA The E coliculture was then shifted into medium containing the common light isotope of nitrogen 14N and allowed to grow for one generation The cells were harvested and the DNA was isolated The DNA was centrifuged at high speeds in an ultracentrifuge in a tube in which a cesium chloride density gradient had been established Some cells were allowed to grow for one more life cycle in 14N and spun again During the density gradient ultracentrifugation the DNA was loaded into a gradient Meselson and Stahl used a gradient of cesium chloride salt See Answer

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