Concept explainers
In the Meselson-Stahl experiment, which of the three modes of replication could be ruled out after one round of replication? after two rounds?
To determine: The reason that in the Meselson– Stahl experiment among the three modes of replication, the mode of replication that could be ruled out after oneround of replication.
Introduction: Messelson and Stahl experiment explained that semiconservative mode of replication used by bacterial cells to produce new DNA molecules.
Explanation of Solution
Messelson grew the E. coli cells for many generations in a medium containing 15NH4Cl. These cells then transferred to 14NH4Cl. After one round of replication, the conservative mechanism of DNA replication was ruled out as the intermediate density of DNA band found in the solution. DNA undergoes the semiconservative mode of replication.
Thus, the conservative mode of replication can be ruled out after one round of replication in case of Meselshon Stahl experiment.
To determine: The reason that in Meselson– Stahl experiment among the three modes of replication the mode of replication that could be ruled out after the second round of replication.
Introduction: Messelson and Stahlstudied the modes of DNA replication in bacteria by using nitrogen and its isotope in the medium. Bands of DNA replication was studied after each round of replication.
Explanation of Solution
Messelson grew the bacterial DNA in N15 and N14 media. After one round of replication in14N media, the band of the intermediate density of DNA was found.
After the second round of replication in14N media, the dispersive model of DNA replication was ruled out. The density of the DNA after the second round of replication was between the intermediate (both dark and light band) and “light” densities of DNA.
Thus, the dispersive model of DNA replication was ruled out after the second round of replication.
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Chapter 11 Solutions
Concepts of Genetics (12th Edition)
- he Meselson and Stahl experiment provided conclusive evidence for the semiconservative replication of DNA in E. coli. What pattern of bands would they have observed in a CsCl gradient after one generation if replication was conservative? a heavy, a light and an intermediate band one heavy and one light band (no intermediate) one intermediate band one light band one heavy bandarrow_forwardIn the Meselson-Stahl experiment on DNA replication, what fraction of the DNA was composed of one light strand and one heavy strand ("hybrid") after one generation of growth in medium containing 14N? After two generations of growth in a medium containing 14N? What fraction of hybrid DNA is expected after n generations of growth in a medium containing 14N?arrow_forwardIn terms of the new DNA strands that are generated, what are the differences between replication and conventional polymerase chain reaction?arrow_forward
- Is it biologically possible for DNA to undergo replication in vivo, without the lagging and the leading strands? In PCR, we also start with an antiparallel strand of DNA. Does this also mean that replication is semi-discontinuous in in vitro replication?arrow_forwardWhat are the three models of DNA replication? With the aid of illustrations, show how the Meselson Stahl experiment come to the conclusion of one model of DNA replication. Is DNA replication bidirectional? How did you arrive at this conclusion? Explain the bacterial replication model that supports this conclusion.arrow_forwardWhat would happen if, in the course of replication, thetopoisomerases were unable to reattach the DNA fragments of each strand after unwinding (relaxing) theDNA molecule?arrow_forward
- If DNA replication followed the dispersive model of replication, how would the outcomes of the Meselson-Stahl experiment change? Describe the composition of DNA samples after one and two rounds of replication, and how this is different from the findings of the original experiment.arrow_forwardWhy is a clamp loader necessary in replication?arrow_forwardIf the four deoxynucleotides showed nonspecific basepairing (A to C, A to G, T to G, and so on), would theunique information contained in a gene be maintainedthrough round after round of replication? Explainarrow_forward
- In terms of new DNA strands that are generated, what are the differences between replication and conventional polymerase chain reactions?arrow_forwardWhy is the replication of DNA referred to as a semiconservative process? What is the experimental evidence for the semiconservative nature of the process? What experimental results would you expect if replication of DNA were a conservative process?arrow_forwardThe Meselson-Stahl experiment provided strong evidence that DNA replication was conservative, by alternately growing bacteria in medium with heavy 15N and light 14N. If DNA replication were dispersive, what result would Meselson and Stahl have observed after the first round of DNA replication in light nitrogen? Group of answer choices Two bands, one at the location for pure 15N and one at the location for pure 14N. One band, located half way between the locations for pure 15N and pure 14N. Two bands, one at the location for pure 15N and one located halfway between the locations for pure 15N and pure 14N. None of these Three bands, one at the location for pure 15N, one at the location for pure 14N, and one at a location halfway between.arrow_forward
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