DNA Replication (2.11) Flashcards
Describe the process of DNA replication
The double helix of DNA unwinds and an enzyme known as helicase helps unzip (breaks hydrogen bonds that join base pairs) and separate the DNA into its two separate strands.
From here free nucleotides bond to their complimentary base pairs on the exposed strand.
DNA polymerase joins the new nucleotides with strong phosphodiester bonds, forming a strong sugar-phosphate backbone.
Explain how Meselson and Stahl’s experiment provides evidence for the semi-conservative model of DNA replication
By exposing the bacteria DNA that had 15 nitrogen to a medium that had 14 nitrogen, and spinning it through the centrifuge, it showed that the density of the DNA changed and became lighter once exposed. Supporting the idea that the new strand consisted of half the original and half of a new strand.
Explain how Meselson and Stahl’s experiment refuted the conservative model of DNA replication
In the conservative model, the two parental strands of DNA rejoin, after acting as templates for the new DNA strands. This means the parental double helix is restored. This is refuted but meselson and stahl as the findings in density prove that he be strands involve the two separate nitrogen contained strands.
Explain how Meselson and Stahl’s experiment refuted the dispersive model of DNA replication
It was found that there were DNAs of two different densities, unlike the first time when there were three. One of the two had intermediate density just like in the previous experiment and the second one had the density of pure 14N isotope.
This result did not support the dispersive hypothesis of replication as it would have given one DNA having a density lower than the intermediate density found in the experiment.
