The Hershey-Chase Experiment - Online Tutor, Practice Problems & Exam Prep

The Hershey-Chase experiment in 1952 confirmed that DNA, not protein, is the genetic material. Using bacteriophages, scientists labeled viral proteins with radioactive sulfur and DNA with radioactive phosphorus. They found that only the viral DNA entered bacterial cells during infection, while the protein coat remained outside. This pivotal experiment resolved the debate over the genetic material, establishing DNA as the carrier of genetic information, which is fundamental to understanding molecular biology and genetics.

Bacteriophages

This video, we're going to begin our lesson on the Hershey Chase experiment. It's important to recall from our previous lesson videos that even after the Griffith experiment and subsequent experiments showed that DNA is the genetic material, many scientists still remained skeptical that DNA could be the genetic material, and they felt that proteins were actually a better candidate to be the genetic material. It wasn't until 1952, when the scientists Alfred Hershey and Martha Chase used bacteriophages to confirm that DNA actually is the genetic material. And it wasn't until this Hershey Chase experiment that most scientists were convinced that DNA is the genetic material, not protein.

Hershey and Chase used bacteriophages to help them confirm that DNA was the genetic material. But what are these bacteriophages? Well, bacteriophages are also sometimes referred to as just phages. Bacteriophages and phages are the same thing. They are a virus that replicates itself by infecting and hijacking bacteria. In our image below, we're showing you a representation of what a bacteriophage actually looks like. It's this pink structure that you see here. Typically these bacteriophages consist of an external protein coat surrounding a nucleic acid core in the center. In our image, this bacteriophage consists of an external protein coat, and within this external protein coat, you can see that the nucleic acid core is represented. The nucleic acid here represents DNA in this scenario. These bacteriophages infect bacterial cells, as shown in our image below.

Today, we know that bacteriophages operate by injecting the nucleic acid into the bacterial cell. However, in the 1950s, it was not clear exactly how these bacteriophages operated. Some scientists thought that perhaps it was the protein that actually makes its way into the bacterial cell. The Hershey Chase experiment revealed how the bacteriophages worked, and that revelation helped to confirm that DNA is the genetic material. We will talk more about the details of the Hershey Chase experiment in our next video. For now, this concludes our introduction to the Hershey Chase experiment and how bacteriophages were used. I'll see you in our next video to learn more.

The Hershey-Chase Experiment

So now that we briefly introduced bacteriophages, in this video we can focus more on the details of the Hershey Chase experiment. The biggest takeaway that you should get from this Hershey Chase experiment is that the scientists Hershey and Chase were able to show that only viral DNA and not viral protein actually enters the bacteria during a bacteriophage infection. The fact that only viral DNA and not viral protein enters bacteria during a bacteriophage infection was evidence to confirm that DNA, not protein, is actually the genetic material. And so it was the Hershey Chase experiment that pretty much ended the controversy of what was the genetic material, DNA or protein. And again, the Hershey Chase experiment validated and confirmed that it was DNA that is the genetic material, not protein.

And so if we take a look at our image down below, it's showing you some of the details of the Hershey Chase experiment. Really, what they did was they took these bacteriophages and separated them into two groups. One group is over here on the left-hand side and the other group of bacteriophages over here on the right-hand side. On the left-hand side, they took the bacteriophages and used radioactive sulfur labels to label the viral protein coat that's on the external of the bacteriophage. What you can see is that the radioactive protein shell is labeled and highlighted with this yellow border. Over here on the right-hand side, what they did was they took bacteriophages and used radioactive phosphorus labels instead of radioactive sulfur labels. The radioactive phosphorus labels would label the viral DNA. Notice that it's only the viral DNA that's highlighted here in yellow that's at the core of the bacteriophage.

Using these radioactive labels, they were able to track and trace these viral particles during a bacteriophage infection. What they noticed was that during the bacteriophage infection, the radioactively labeled protein shell, the radioactively labeled viral protein coat, would always remain on the outside of the cell. They would never find traces of the radioactively labeled protein on the inside of the cell. And, of course, when they radioactively labeled the DNA, what they saw was that the radioactively labeled DNA was found on the inside was evidence to suggest and confirm that it was the viral DNA that acted and served as the genetic material.

Once again, the biggest takeaway here of the Hershey Chase experiment was that it ended the controversy of what was the genetic material, DNA or protein. And it confirmed that DNA is the genetic material. This here concludes our lesson here on the Hershey Chase experiment, and we'll be able to get some practice applying these concepts as we move forward in our course. So, I'll see you all in our next video.

Hershey and Chase set out to determine what molecule served as the unit of inheritance. Which molecular component of the T2 virus actually ended up inside the cell?

• A. The protein coat.
• B. RNA.
• C. Ribosome.
• D. DNA.

Choose the incorrect statement about the results of the Hershey-Chase Experiment.

• A. Radioactive labeled protein was found in the bacteria.
• B. Radioactive labeled DNA was found in the bacteria.
• C. DNA was labeled with radioactive phosphorus.
• D. Protein was labeled with radioactive sulfur.
• E. Radioactive labeled protein was found outside of the bacteria.

Which of the following facts did Hershey and Chase make use of in trying to determine whether DNA or protein is the genetic material?

• A. DNA contains sulfur, whereas protein does not.
• B. DNA contains phosphorus, whereas protein does not.
• C. DNA contains nitrogen, whereas protein does not.
• D. DNA contains purines, whereas protein includes pyrimidines.

Here’s what students ask on this topic:

What was the main conclusion of the Hershey-Chase experiment?

The main conclusion of the Hershey-Chase experiment was that DNA, not protein, is the genetic material. By using bacteriophages labeled with radioactive sulfur to mark proteins and radioactive phosphorus to mark DNA, Hershey and Chase demonstrated that only the viral DNA entered bacterial cells during infection. This finding provided strong evidence that DNA is the carrier of genetic information, resolving the debate over whether DNA or protein served this role.

How did Hershey and Chase use radioactive labeling in their experiment?

Hershey and Chase used radioactive labeling to distinguish between viral DNA and protein. They labeled the protein coat of bacteriophages with radioactive sulfur (³⁵S) and the DNA with radioactive phosphorus (³²P). During infection, they observed that the radioactive phosphorus entered the bacterial cells, while the radioactive sulfur remained outside. This indicated that DNA, not protein, was injected into the bacteria, confirming that DNA is the genetic material.

Why were bacteriophages used in the Hershey-Chase experiment?

Bacteriophages were used in the Hershey-Chase experiment because they are viruses that infect bacteria, making them ideal for studying the transfer of genetic material. Bacteriophages consist of a protein coat surrounding a DNA core. By using these viruses, Hershey and Chase could easily separate and track the protein and DNA components during infection, allowing them to determine which molecule carried the genetic information.

What role did radioactive sulfur and phosphorus play in the Hershey-Chase experiment?

In the Hershey-Chase experiment, radioactive sulfur (³⁵S) was used to label the protein coat of bacteriophages, while radioactive phosphorus (³²P) was used to label the DNA. These radioactive markers allowed Hershey and Chase to trace the fate of the protein and DNA during infection. They found that only the radioactive phosphorus entered the bacterial cells, indicating that DNA, not protein, is the genetic material.

How did the Hershey-Chase experiment resolve the debate over the genetic material?

The Hershey-Chase experiment resolved the debate over the genetic material by providing clear evidence that DNA, not protein, is the carrier of genetic information. By using radioactive labeling to track the movement of DNA and protein during bacteriophage infection, they demonstrated that only DNA entered the bacterial cells. This finding convinced the scientific community that DNA is the genetic material, ending the controversy that had persisted despite earlier experiments.