Download Hershey Chase Activity

Hershey/Chase Experiment
Honors BioMed 2
Redwood High School
*Vocab: Tagging; Supernatant
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W
hat Hershey and Chase did not know is which viral component - DNA or protein - was responsible for
reprogramming the host bacterial cell. If an answer could be found they would resolve the debate over which
macromolecule class was responsible for heredity. They answered this question by performing the experiment
described below.
1. Working in lab groups, create and label a diagram reflecting the experimental protocol and results
(use the 11x17 paper provided)
2. Review the four (4) conclusions listed. Respond in writing to each. Using numbered responses, agree or
disagree with each, and explain your position.
Experiment Protocol:
Step 1:
Viral protein and DNA were tagged separately with different radioactive isotopes.
Ø Protein Tagging: T2 phage grown in E.coli liquid culture containing radioactive sulfur (35S)
which incorporated only into proteins – as sulfur is common element found in proteins.
Ø DNA Tagging: T2 phage grown in E. coli liquid culture containing radioactive phosphorus (32P)
which was incorporated only into DNA – as phosphorous is a common element found in DNA.
Ø special note: sulfur is not present in DNA and phosphorous is not present in proteins
Step 2:
Protein-Tagged, and DNA-Tagged, T2 phages (separated from their step 1 hosts) were allowed to
infect separate cultures of non-radioactive E. coli cells.
Step 3:
Cultures were agitated to shake loose phages that remained outside the bacterial cells.
Step 4:
Mixtures were centrifuged forcing the heavier bacterial cells into a pellet on the bottom of the tubes.
The lighter viruses remained in the supernatant.
Step 5:
Radioactivity in the pellet (more dense – solids) and supernatant (the less dense aqueous solution)
was measured and compared.
Results:
1
In the tube with E. coli infected with protein-labeled T2, most of the radioactivity was in the supernatant
with viruses.
2. In the tube with E. coli infected with DNA-labeled T2, most of the radioactivity was in the pellet with the
bacterial cells.
3. When the bacteria containing DNA-labeled phages were returned to culture medium, the bacteria released
phage progeny that contained 32P in their DNA.
Conclusions:
1. Viral proteins remain outside the host cell.
2. Viral DNA is injected into the host cell.
3. Injected DNA molecules cause cells to produce additional viruses with more viral DNA and proteins.
4. These data provided inconclusive evidence that nucleic acids, rather than proteins are the hereditary
material.