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6 Cards in this Set

  • Front
  • Back

How is DNA replicated and who discovered this?
  • Semiconservative replication
  • Meselson + Stahl in 1959

Describe the Meselson-Stahl experiment
  • Bacteria grown on heavy N15
  • DNA extracted and cetrifuged
  • DNA became labelled with 15N and settled at different heights in density gradient centrifugation
  • Samples from different generations show that DNA replication is semi conservative

Problems with unwinding DNA strands
  • DNA would have to rotate at 20,000 revs/minute in a typical bacterium
  • this would generate heat that would burst the bacterium

How are DNA strands separated?
  • Topoisomerases

Describe the action of DNA topoisomerase 1
Makes a nick in one strand of DNA second strand passes through nick opens up strand in order for replication and releases stress
  • Makes a nick in one strand of DNA
  • second strand passes through nick
  • opens up strand in order for replication and releases stress

Describe the action of DNA topoisomerase II
  • Makes a cut through a double stranded molecule when DNA is supercoiled
  • Second DNA molecule passes through cut
  • Tension is relieved in the molecule