The Hershey–Chase Experiment


In 1952, Alfred Hershey and Martha Chase published a convincing demonstration the DNA (not protein) was the hereditary material. The Hershey–Chase experiment was carried out through a virus, dubbed bacteriophage T2, the infects bacteria. Bacter T2 consists of little an ext than a DNA main point packed inside a protein coat. Thus, the virus is do of the two materials that were, at the time, the top candidates because that the genetic material.

1The Hershey–Chase experiment was based on the biologic of a virus, dubbed bacteriophage T2, that attacks a bacterium. The virus consists of DNA core packed inside a protein coat.

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2Part (but not all) of the virus enters the bacterial cell. About 20 minutes later, the cell bursts, release dozens of corpuscle that are virtually identical to the infecting virus particle. Hershey and also Chase deduced the the entrance of some viral ingredient affects the genetic program of the hold bacterial cell, transforming it into a bacteriophage factory. They collection out to recognize which component of the virus—DNA or protein—enters the bacterial cell.

3To trace the two contents of the virus over its life cycle, Hershey and also Chase labeled each component through a specific radioisotope. They offered 32P to brand DNA. The 2 strands that DNA have actually a sugar-phosphate backbone that consists of phosphorus atoms. Phosphorus is not present in most proteins. They used 35S to brand proteins. Protein contain part sulfur, due to the fact that sulfur is discovered in the amino acids cysteine and also methionine. Sulfur is not present in DNA.

4After farming the virus in the visibility of either 32P or 35S, the two radioactive famous samples were added along v the organize bacteria come fresh society medium. The viruses were given sufficient time to epidemic the bacteria, after which the culture medium to be agitated in a blender come detach the viruses native the bacter cells.

5Samples were then placed in tubes and also centrifuged to force the bacterial cell to the bottom that the tube, forming a pellet. The supernatant fluid consists of the viruses.

6In each of this samples, the radiation component will be in a various fraction, one of two people the pellet or the supernatant. If DNA is, in fact, the genetic material, predict i m sorry of the 2 tubes—the one v 32P or the one v 35S—will have actually a radioactive pellet. Click on the correct tube.

7Hershey and also Chase uncovered that most of the 32P is in the pellet with the bacteria, while most of the 35S is in the supernatant liquid with the viruses. Since the 32P labeling the DNA, the researchers concluded that DNA, not protein, enters bacterial cells and also directs the assembly of brand-new viruses. The is, DNA is the genetic material.

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In addition to the experiment described in this tutorial, Hershey and also Chase performed similar but longer-term experiments, permitting the progeny (offspring) generation that viruses to reproduce in unlabeled bacteria. The result viruses contained virtually no 35S and none of the parental viral protein. Castle did, however, contain around one-third the the original 32P—and thus, presumably, one-third that the original DNA. Since DNA was carried over in the viruses indigenous generation to generation yet protein was not, the reasonable conclusion was the the hereditary information was included in the DNA.