DNA REPLICATION

• What type of replication does DNA undergo?

  Semi-conservative
• What does semi-conservative replication mean?


  Half of the strand is the old DNA, half is the newly replicated strand.
• Process:

  • DNA helicase breaks open H bonds separating the two strands of DNA
  • Free RNA nucleotide bases bind specifically to their complementary bases
  • Phosphodiester backbone created by DNA polymerase in a series of condensation reactions
  • two identical molecules of DNA are formed
• Evidence for semi-conservative replication

  • All DNA bases contain nitrogen, which has two forms (lighter 14N and isotope 15N which is heavier
  • Bacteria incorporate nitrogen from their growing medium into any new DNA they make
  • Centrifuged extracted DNA and found by analysing test tubes that half new and half old DNA was present (as lighter 14N would sit higher than isotope 15N