Advertisements
Advertisements
Question
Describe the experiment that helped demonstrate the semi-conservative mode of DNA replication.
Solution
Experiment
The experiment was performed by Meselson and Stahl. The following steps were followed in the experiment:
- E. coli was grown in a medium containing the heavy isotope 15N as the sole nitrogen source. This led to the incorporation of 15N into the newly synthesised DNA, which ultimately made the DNA heavy.
- This heavy DNA was seperated from the normal DNA by density gradient centrifugation using cesium chloride as the gradient.
- The cells were then transferred into a medium with 14N as the nitrogen source. Samples were taken from this medium and the DNA was extracted.
Observation
Since E. coli divides every 20 minutes, the DNA extracted after 20 minutes in the experiment had a hybrid density.
The DNA extracted after 40 minutes had equal amounts of hybrid and light densities.
Conclusion
This implies that the newly synthesised DNA obtained one of its strands from the parent. Thus, replication was semi-conservative.
APPEARS IN
RELATED QUESTIONS
Describe Meselson and Stahl’s experiment that was carried in 1958 on E.Coli. Write the conclusion they arrived at after the experiment.
Explain the process of DNA replication with the help of a schematic diagram.
Draw a diagrammatic sketch of a portion of DNA segment to support your answer.
DNA replication is ______.
If Meselson and Stahl's experiment is continued for four generations in bacteria, the ratio of `15_N/15_N:15_N/14_N:14_N/14_N` containing DNA in the fourth generation would be ______.
In order to form a dinucleotide during DNA synthesis which functional group at 3' must be free?
The experimental proof for semi-conservative replication of DNA was first shown in a ______
Discuss the significance of heavy isotope of nitrogen in the Meselson and Stahl’s experiment.
During which phase of the cell cycle, does DNA replication take place?
The DNA molecules of the same size were extracted from E. coli and Plasmodium vivax. It was discovered that both the DNA molecules had one target site each for the restriction enzyme Hind II. After being digested with Hind II, the DNA fragments were subjected to gel electrophoresis.
With reference to the diagram given below, identify the lanes that represent the DNA fragments of E. coli and Plasmodium vivax respectively. Justify your answer with a reason for each.
