Question

Bacteriophages were used to provide evidence that DNA carries genetic information (see Figure 16.4). Briefly describe the experiment carried out by Hershey and Chase, including in your description why the researchers chose to use phages.

Short answer

Hershey-Chase chose the T2 phage for their experiment because its genetic material was made of DNA and protein.

In the experiment, Hershey and Chase infected two groups of E.coli, one each with radioactive phosphorus labeled virus and radioactive sulfur labeled virus. The set of samples was then observed to check whether DNA or protein had entered the cell.

It was found that DNA had entered the cell as the progeny obtained produced contained radioactively labeled phosphorus in their genetic material.

Step-by-step solution

Hershey and Chase selected T2 phage for their experiment

Viruses that infect bacteria are called bacteriophages. Most viruses contain RNA as the genetic material; however, T2 bacteriophage contains DNA as the genetic material.

For this reason, Hershey and Chase chose a T2 bacteriophage to infect E.coli as its genetic material was made of DNA and protein. DNA and protein are two types of macromolecules that are expected to be present in the genetic material of an organism.

Hershey and Chase Experiment

Hershey and Chase were aware that the genetic material of the T2 phage was made of DNA and protein. Thus, he selected two mediums to grow the viruses. One medium contained radioactive sulfur as sulfur is present in proteins but not DNA.

While the other medium contained radioactive phosphorus as phosphorus was present in DNA but not proteins. As a result, two groups of viruses were obtained. One group of viruses contained radioactive sulfur in their proteins, while another set contained radioactive phosphorus labeled DNA.

These groups of labeled viruses were then allowed to infect two sets of E.coli cells.

Observation of the experiment

Hershey and Chase collected the viral progenies of the two E. colisets and observed that progenies contained radioactive phosphorus in their DNA as phosphorus is a component of DNA.

The radioactive phosphorus entered the cell while radioactive sulfur remained outside the cell. Thus, it was concluded that DNA is the genetic material because radioactively labeled phosphorus entered the cell, and it was present in the virus's genetic material.