Video Transcript
The diagram provided shows a simple
outline of an experiment carried out by Hershey and Chase. They radioactively labeled
different parts of a bacteriophage, a virus that infects bacterial cells, to
determine what material was used to infect bacteria. What did the experiment
determine? (A) Proteins are the genetic
material transferred to bacteria. (B) DNA is the genetic material
transferred to bacteria. (C) DNA and proteins are
transferred from bacteriophages to bacteria. Or (D) bacteriophages only infect
bacterial cells that do not contain DNA.
This question asks us about a
famous experiment carried out by Alfred Hershey and Martha Chase in 1952. In order to answer the question
correctly, let’s review what these experiments entailed. Hershey and Chase utilized
bacteriophages. As indicated by their name, these
are viruses that infect bacterial cells. You might recall that viruses
require a host cell, like a bacteria, to replicate and proliferate. Hershey and Chase knew that these
viruses were made of two parts: the protein shell and the viral DNA inside. But Hershey and Chase did not know
how bacteriophages infect the bacteria: was it by transferring their DNA or their
proteins?
In order to determine this, Hershey
and Chase radioactively labeled these two different components of the bacteriophage,
the proteins and the DNA, with different radioactive markers called isotopes. Because DNA contains high amounts
of phosphorus, Hershey and Chase used radioactively labeled phosphorus to visualize
this component. On the other hand, they used
radioactively labeled sulfur in order to visualize proteins such as the capsid. This is because proteins, but not
DNA, contain the unique molecule sulfur in some of their amino acids.
With these differentially labeled
bacteriophages, Hershey and Chase then infected bacterial cells. And afterward, they centrifuged the
resulting solution in order to separate cells from viral particles. Only the radioactively labeled DNA
was detected inside the bacterial cells. This is because bacteriophages
transmit genetic information during infection. Their protein structures, such as
capsids, do not enter the cell, so these were only visualized in the layer
containing viral particles.
Now that we have reviewed the
experiments of Hershey and Chase, we are able to correctly answer this question. The correct answer is (B). The experiment determined that DNA
is the genetic material transferred to bacteria.