• Created by: aaishak
  • Created on: 01-03-15 08:09
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    • method
      • 1) the original DNA double helix unzips by the DNA helicase enzyme which breaks the hydrogen bonds between the bases.
      • 2) there are free nucleotides in the nucleoplasm and they attach themselves to the old strand by complementary base pairing.
      • 3)the base pairs are joined together by hydrogen bonds. between a C and G there are 3 hydrogen bonds while between a T and A there are 2 hydrogen bonds.
      • 4)to join the nucleotides together they use the enzyme DNA polymerase to create strong phosphodiester bonds between the nucleotides.this then produces a sugar phosphate backbone.
      • 5)another enzyme is then used to wind the new strand into a double helix. this is how each DNA molecule consists of both an old and new strand naming it semi-conservative.
    • DNA is replicated before cell division so that one identical  copy can go in each daughter cell.
    • the melson-stahl experiment.
      • 1) in a heavy medium where you only have the old DNA(so just conserved DNA) its heavy so it falls to the bottom.
      • 2) after its been replicated and its in a light medium it stays in the middle as there is old and new DNA so (heavy and light DNA) its semi-conservative now.
      • Old DNA is heavy DNA while new DNA is light DNA.
      • 3) after the replicated DNA has been replicated again there is a pair of 2 light DNA and also a pair of semi-conservative DNA in the light medium.
      • 4)The 2 light DNA stay at the top while the semi-conservative DNA stays at the middle in the light medium.


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