Hershey and Chase Experiment

In 1952, Alfred Hershey and Martha Chase investigated bacteriophage, a virus that destroys bacteria. Their research focused on T2 bacteriophage that infects the bacterium Escherichia coli (E. coli). Their goal was to determine whether the T2 phage’s genetic instructions or information required for life, were stored in its DNA or protein coat. They wanted to show that the DNA, not the protein, contained this important genetic information.

There were three steps in the experiment:

1. Infection
2. Blending
3. Centrifugation

Alfred Hershey and Martha Chase used two forms of radioactive material, phosphorus-32 (32P) and sulfur-35 (35S), to designate the bacteriophages differently. Phosphorus is a component of DNA, the genetic material, whereas sulphur is present in proteins but not DNA.

They inserted these radioactive isotopes into the bacteriophages DNA (genetic material) and protein coat (capsid) separately. This enabled them to determine which parts of the virus entered the bacterial cell during infection. They then allowed the labelled viruses to infect E. coli bacterial cells.

Following a brief time of infection, they mixed the liquid to separate the viral protein coatings from the bacteria. This blending phase ensured that any viral proteins that were not bound to bacterial cells were eliminated. They next centrifuged the mixture, causing the heavier bacterial cells to sink at the bottom of the tube while the lighter viral protein coatings (if present) remained in the liquid above, known as the supernatant.

The results demonstrated that bacterial cells infected with phages labelled with phosphorus-32 (32P) exhibited radioactivity. This suggested that the phages’ DNA entered the cells during infection. In contrast, bacterial cells infected with phages labelled with sulfur-35 (35S) exhibited little to no radioactivity, indicating that the phages’ protein coat (also known as capsid) did not enter the cells.

Based on these findings, Hershey and Chase concluded that DNA, rather than protein, serves as the genetic material transmitting bacteriophages’ hereditary information. This experiment offered solid proof that DNA is the chemical responsible for conveying genetic information in living beings.

The Hershey and Chase Experiment, conducted in 1952 by Alfred Hershey and Martha Chase, demonstrated that DNA contains genetic information. They accomplished this by investigating viruses that infect bacteria, known as bacteriophages. In these tests, scientists labelled the virus’s DNA with a radioactive marker while labelling the protein coat independently with another marker.

When the viruses infected bacteria, researchers discovered that only the DNA identifier, not the protein marker, was passed along to the next generation of viruses. This helped to demonstrate that DNA, not protein, is the molecule that conveys genetic instructions. We will read about the Hershey and Chase Experiment in detail in this article.