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Hershey-Chase experiment


The Hershey-Chase experiment was a series of experiments conducted in 1952 by Alfred Hershey and Martha Chase that identified DNA to be the genetic material of phages and, ultimately, of all organisms. A phage is a small virus that infects bacteria. It consists of a protein coat that encloses the genetic material. When a phage infects a bacterium, it inserts its genetic material into the bacterium, while its coat remains outside.


In a first experiment, T2 phages with radioactive 32P-labeled DNA infected bacteria. In a second experiment, T2 phages with radioactive 35S-labeled protein infected bacteria. In both experiments, bacteria were separated from the phage coats by blending followed by centrifugation. In the first experiment, most radioactivity was found in the infected bacteria, while in the second experiment most radioactivity was found in the phage coat. These experiments demonstrated that DNA is the genetic material of phage and that protein does not transmit genetic information.

Hershey shared the 1969 Nobel Prize in Physiology or Medicine for his discoveries concerning the genetic structure of viruses


More detailed description

Hershey and Chase knew that T2 consisted of only DNA and protein, and that they somehow manipulated host cells to produce new phages, but did not know if DNA or protein was responsible.

Hershey and Chase radioactively labeled E.Coli and T2 with 32P (phosphorus isotope) and 35S (sulfur isotope) because they knew DNA contains phosphorus, and protein contains sulfur, but not vice versa.

They infected the 32P E.Coli with 32P T2 and 35S E.Coli with 35S T2, and collected the progeny. The results found that the progeny collected from the 32P E.Coli and 32P T2 contained the 32P isotope, while the 35S strains did not, providing more evidence that DNA was the genetic information that bacteriophages inject into bacteria, not protein.


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