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Biochemistry 3107: Week 4 Tutorial. Phil Williams [email protected] 777-6878 HSC4333. Hershey-Delbruck Experiment. E. coli was infected with two strains of bacteriophage T2. One strain is h-r+ ; One strain is h+r-. Hershey-Delbruck Experiment.

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hershey delbruck experiment
Hershey-Delbruck Experiment
  • E. coli was infected with two strains of bacteriophage T2.
    • One strain is h-r+;
    • One strain is h+r-
hershey delbruck experiment3
Hershey-Delbruck Experiment
  • h locus determines whether the phage can grow on a particular strain of E. coli
    • phage that are h- can infect the strain
    • phage that are h+ cannot infect the strain
  • r locus is a gene that determines whether the phage will lyse the host cells rapidly or slowly
    • phage that are r- will lyse the host cells rapidly
    • phage that are r+ will lyse the host cell slowly
hershey delbruck experiment4
Hershey-Delbruck Experiment
  • two strains of E. coli were used in the experiment
    • strain 1 supports growth of h- phage but not h+ phage
    • strain 2 supports the growth of both phage
hershey delbruck experiment5
Hershey-Delbruck Experiment
  • Bacteriophage are plated on a lawn of bacteria that consists of a mixture of both strains of E. coli
  • Expect two different phenotypes:
    • Both strains infected: Clear plaques
    • Infect only one of the two strains: Turbid plaques
hershey delbruck experiment proves
Hershey-Delbruck Experiment Proves:
  • If an E. coli cell was infected at the same time with two genetically different bacteriophage, the resulting phage population included recombinant phage types as well as the original parental phage types
  • The Nobel Prize in Physiology or Medicine 1969
meselson weigle experiment
Meselson-Weigle Experiment
  • First demonstrated that both strands of each molecule must be broken and then rejoined in 1961
meselson weigle experiment9
Meselson-Weigle Experiment
  • Infected E. coli cells at the same time with phage from two different stocks of bacteriophage lambda.
    • Bacteriophage lambda c- mi-
      • Heavy isotopes of carbon 13C and nitrogen 15N
    • Bacteriophage lambda c+ mi+
      • Light isotopes of carbon and nitrogen
meselson weigle experiment12
Meselson-Weigle Experiment
  • Phenotypes of the intermediate density phage were recombinant phages
    • c- mi+ found near the band of "heavy“ non- recombinant phage
    • c+ mi- found near the band of "light" non- recombinant phage.
meselson weigle experiment13
Meselson-Weigle Experiment
  • These results can only be explained if recombination between the two parental phage involves breakage and rejoining of both DNA strands
holliday model
Holliday Model
  • Holliday Model
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