Hershey Chase Experiments




Hershey and Chase knew that T4 bacteriophages consist of proteins and DNA. They asked which viral component must enter a bacterial cell to infect it: DNA or protein? They grew viruses with either radioactive sulfur, which labels the viral protein, or radioactive phosphorus, which labels DNA. The radioactively labeled viruses were allowed to infect bacteria. After infection, empty shells of viral particles remained attached to the bacterial wall. To shake these particles loose, the cultures were whirled in a blender. After the blender treatment, the bacteria infected by the sulfur-labeled viruses did not contain radioactive sulfur. The sulfur-labeled protein was outside of the cell. In contrast, bacterial cells infected by a phosphorus-labeled virus did contain radioactive DNA. This was strong evidence that DNA, not protein, is injected during infection and is the genetic material of this type of virus.



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