1.7 DNA replication

• Why does DNA replicate?

  genetic info remains consistent throughout an organism
• Enzymes involved

  • helicase
  • DNA polymerase
• Semi conservative replication

  1. original helix untwists
  2. Hydrogen bonds break
  3. Free nucleotides attracted to complementary bases on each strand, requires energy from ATP
  4. DNA polymerase joins the backbone, catalysing phosphodiester bonds to form
  5. The two strands twist separately to form two DNA helices.
• How did Medelson and Stahl prove semi conservative replication?

  • Grew ecoli in a medium containing heavy nitrogen (N15)
  • Then put the bacteria in a medium containing light nitrogen (N14)
  • Used ultracentrifugation to separate the DNA
  • Was able to see the difference in weight as it separated by density