The 1952 Hershey-Chase experiment definitively established DNA as the hereditary genetic material, superseding protein. This experiment utilized bacteriophages, viruses that infect bacteria, amidst a prevailing scientific debate regarding whether proteins or nucleic acids (DNA or RNA) served as the primary carriers of genetic information. Hershey and Chase's research resolved this uncertainty.
Step 1: The Experimental Design.
To determine whether the bacteriophage's protein coat or its DNA entered the bacterial cell and transmitted genetic information, Hershey and Chase employed two distinct radioactive isotopes:
\( ^{32}P \) (radioactive phosphorus) was used to label DNA, as phosphorus is a constituent of DNA but absent in proteins.
\( ^{35}S \) (radioactive sulfur) was used to label proteins, as sulfur is present in proteins but absent in DNA.
These isotopically labeled bacteriophages were then introduced to infect *Escherichia coli* (E. coli) bacteria, serving as the host organisms.
Step 2: Separation of Viral Components.
Following the infection of bacteria by bacteriophages, Hershey and Chase employed a blender to dislodge the viral protein coats from the bacterial cells. This mechanical action detached the phage coats from the host cells. Subsequently, centrifugation was used to separate the denser bacterial cells, containing the genetic material, from the less dense protein coats, which remained in the liquid supernatant.
Step 3: Key Observations and Conclusion.
The critical findings of the experiment were as follows:
The radioactive phosphorus (\( ^{32}P \)) originating from the DNA was detected within the bacterial cells, signifying that the bacteriophage's DNA had entered the bacteria during the infection process.
The radioactive sulfur (\( ^{35}S \)) remained in the supernatant, indicating that the protein component had not penetrated the bacterial cells.
These results conclusively demonstrated that DNA, not protein, conveyed the genetic instructions necessary for the bacteriophage's replication within the host bacterium.
Consequently, the Hershey-Chase experiment concluded that \( \mathbf{DNA \, is \, the \, genetic \, material \, in \, bacteriophages.} \)