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✨ replication of DNA ✨
it is now proven that DNA replicates semiconservatively.
⏩Mathhew Meselson and Franklin Stahl performed the experiment in 1958 .
following experiment:
- they grew E.coli in a medium containing (15N is heavy isotope of nitrogen ).
E.Coli was grown in a medium with N-15 for several generations.
- E.coli with only N-15 in their DNA were transferred to a medium with N-14. the various samples were separated independently on CsCl gradients to measure the densities of DNA.
- Cells of E.coli were allowed to divide. Sample was taken and DNA was extracted periodically as cell division continued to check what type of DNA is being formed now.
One replication in E.coli takes around 20 minutes. So, generation I is formed in 20 minutes.
therefore samples are taken after
20 min then again after 40 minutes.
result :
generation 1 : DNA was found to have intermediate density after 1 replication.
generation 2: equal amounts of DNA with different densities are formed .
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