How did Alfred Hershy and Martha Chase arrive at the conclusion that DNA is the
1. Hershey and Chase worked with viruses that infact bacteria called bacteriophages.
2. They grew some viruses on a medium containing radioactive phosphorusand
some on radioactive sulphur ().
3. Viruses grown in radioactive phosphorus contain radioactive DNA but not radioactive protein.
Similarly, viruses grown in radioactive sulphur contain radioactive protein but not radioactive
4. Then they were allowed to infect E.coli bacteria.
5. Soon after infection, the cultures were gently agitated in a blender to seperate the viral coats
from the bacterial cell. Bacteriophage only injects its DNA into the host or bacterial cell.
6. The cultures were then centrifuged. The heavier bacteria settled down in the form of
pellet. The supernatant contains viral coats which do not enter the bacterial cells.
7.It was found that in phage labelled with, radioactivity was detected in supernatant
but not in bacterial cells.
8. In the second culture where bacteriophage labelled with, it was found that radioactivity
detected in bacterial cells not in supernatant.
The Hershey and Chase experiment