Editing Hershey–Chase experiment (section)

==Methods and results==
[[File:Tevenphage.svg|thumb|Structural overview of T2 phage]]
Hershey and Chase needed to be able to examine different parts of the phages they were studying separately, so they needed to distinguish the phage subsections.  Viruses were known to be composed of a protein shell and DNA, so they chose to uniquely label each with a different elemental [[isotope]].  This allowed each to be observed and analyzed separately.  Since phosphorus is contained in DNA but not amino acids, [[radionuclide|radioactive]] phosphorus-32 was used to label the DNA contained in the [[T2 phage]].  Radioactive sulfur-35 was used to label the protein sections of the T2 phage, because sulfur is contained in protein but not DNA.<ref name=":0">{{Citation |title=Hershey-Chase Experiment |date=2008 |url=http://dx.doi.org/10.1007/978-1-4020-6754-9_7525 |encyclopedia=Encyclopedia of Genetics, Genomics, Proteomics and Informatics |pages=865 |place=Dordrecht |publisher=Springer Netherlands |doi=10.1007/978-1-4020-6754-9_7525 |isbn=978-1-4020-6753-2 |access-date=2022-12-19}}</ref>

Hershey and Chase inserted the radioactive elements in the bacteriophages by adding the isotopes to separate media within which bacteria were allowed to grow for 4 hours before bacteriophage introduction. When the bacteriophages infected the bacteria, the [[progeny (genetic descendant)|progeny]] contained the radioactive isotopes in their structures. This procedure was performed once for the sulfur-labeled phages and once for phosphorus-labeled phages.
The labeled progeny were then allowed to infect unlabeled bacteria. The phage coats remained on the outside of the bacteria, while genetic material entered. Disruption of phage from the bacteria by [[Agitator (device)|agitation]] in a blender followed by [[centrifugation]] allowed for the separation of the phage coats from the bacteria. These bacteria were [[lysis|lysed]] to release phage progeny. The progeny of the phages that were labeled with radioactive phosphorus remained labeled, whereas the progeny of the phages labeled with radioactive sulfur were unlabeled. Thus, the Hershey–Chase experiment helped to confirm that DNA, not protein, is the genetic material.<ref name=":0" />

Hershey and Chase showed that the introduction of [[deoxyribonuclease]] (referred to as [[DNase]]), an [[enzyme]] that breaks down DNA, into a solution containing the labeled bacteriophages did not introduce any <sup>32</sup>P into the solution.  This demonstrated that the phage is resistant to the enzyme while intact. Additionally, they were able to [[plasmolysis|plasmolyze]] the bacteriophages so that they went into osmotic shock, which effectively created a solution containing most of the <sup>32</sup>P and a heavier solution containing structures called "ghosts" that contained the <sup>35</sup>S and the protein coat of the virus.  It was found that these "ghosts" could [[Adsorption|adsorb]] to bacteria that were susceptible to T2, although they contained no DNA and were simply the remains of the original viral capsule.  They concluded that the protein protected the DNA from DNase, but that once the two were separated and the phage was inactivated, the DNase could hydrolyze the phage DNA.<ref name=Hershey />

===Experiment and conclusions===
Hershey and Chase were also able to prove that the DNA from the phage is inserted into the bacteria shortly after the virus attaches to its host. Using a high-speed blender they were able to force the bacteriophages from the bacterial cells after [[viral entry|adsorption]]. The lack of <sup>32</sup>P-labeled DNA remaining in the solution after the bacteriophages had been allowed to adsorb to the bacteria showed that the phage DNA was transferred into the bacterial cell.  The presence of almost all the radioactive <sup>35</sup>S in the solution showed that the protein coat that protects the DNA before adsorption stayed outside the cell.<ref name=Hershey />

Hershey and Chase concluded that DNA, not protein, was the genetic material.  They determined that a protective protein coat was formed around the bacteriophage, but that the internal DNA is what conferred its ability to produce progeny inside a bacterium.  They showed that, in growth, protein has no function, while DNA has some function.  They determined this from the amount of radioactive material remaining outside of the cell.  Only 20% of the <sup>32</sup>P remained outside the cell, demonstrating that it was incorporated with DNA in the cell's genetic material.  All of the <sup>35</sup>S in the protein coats remained outside the cell, showing it was not incorporated into the cell, and that protein is not the genetic material.<ref name=Hershey />

Hershey and Chase's experiment concluded that little sulfur-containing material entered the bacterial cell.  However no specific conclusions can be made regarding whether material that is sulfur-free enters the bacterial cell after phage adsorption. Further research was necessary to conclude that it was solely bacteriophages' DNA that entered the cell and not a combination of protein and DNA where the protein did not contain any sulfur.<ref name=Hershey />