The Hershey-Chase Experiment: Videos & Practice Problems

The Hershey-Chase experiment in 1952 demonstrated 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, confirming DNA's role as the genetic material. This pivotal experiment resolved the long-standing debate over whether DNA or proteins were responsible for heredity, solidifying the understanding of DNA's essential function in genetics.

Bacteriophages

In 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 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. 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, and really what they are, they are a virus that replicates itself by infecting and hijacking bacteria. Below in our image, we're showing you a representation of what a bacteriophage actually looks like, and it's this pink structure that you see here. Typically, these bacteriophages consist of an external protein coat. This external protein coat surrounds a nucleic acid core in the center. What you can see here in our image is this bacteriophage consisting of an external protein coat, and within this external protein coat, you can see the nucleic acid core. The nucleic acid here would represent DNA in this scenario. Of course, what these bacteriophages do is they infect bacterial cells. You can see that our bacterial cell is being shown down below here. Now, today, we know that the way bacteriophages operate is they inject the nucleic acid into the bacterial cell. But in the 1950s, they were not sure exactly how these bacteriophages operated. Some scientists thought that perhaps it’s the protein that actually makes its way into the bacterial cell. This Hershey-Chase experiment is the one that really revealed how the bacteriophages worked, and that revelation of how bacteriophages work helped to confirm that DNA is the genetic material. We're going to 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 it used bacteriophages. 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. And so really 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. And so really what they did was they took these bacteriophages. Okay. And they took multiple bacteriophages and separated them into 2 groups. They have the group over here on the left-hand side and the other group of bacteriophages over here on the right-hand side. Now on the left-hand side, they took the bacteriophages and they used radioactive sulfur labels to label the viral protein coat that's on the external of the bacteriophage. And so what you can see is that the radioactive protein shell is labeled and highlighted with this yellow border. And then over here on the right-hand side, what they did was they took bacteriophages and they used radioactive phosphorus labels instead of radioactive sulfur labels. And the radioactive phosphorus labels would label the viral DNA. And so notice that it's only the viral DNA that's highlighted here in yellow that's at the core of the bacteriophage.

And so using these radioactive labels, they were able to track and trace these viral particles during a bacteriophage infection. And so 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. And so 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. And so once again, the biggest takeaway here from 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.

And so 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.

Answer: (D)

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.

Answer: (A)

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.

Answer: (B)

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 the infection of bacterial cells, they observed that the radioactive phosphorus (³²P) entered the cells, while the radioactive sulfur (³⁵S) remained outside. This indicated that DNA, not protein, was injected into the bacteria, confirming that DNA is the genetic material.

Why was the Hershey-Chase experiment important for molecular biology?

The Hershey-Chase experiment was crucial for molecular biology because it provided definitive evidence that DNA is the genetic material. Before this experiment, many scientists believed that proteins were the genetic material due to their complexity. By showing that only DNA entered bacterial cells during bacteriophage infection, Hershey and Chase confirmed that DNA carries genetic information. This discovery laid the foundation for understanding the molecular mechanisms of genetics and heredity.

What are bacteriophages and how were they used in the Hershey-Chase experiment?

Bacteriophages, or phages, are viruses that infect and replicate within bacteria. In the Hershey-Chase experiment, bacteriophages were used to determine whether DNA or protein is the genetic material. Hershey and Chase labeled the protein coat of the phages with radioactive sulfur and the DNA with radioactive phosphorus. By tracking these labels during infection, they found that only the DNA entered the bacterial cells, proving that DNA is the genetic material.

What was the role of radioactive sulfur and phosphorus in the Hershey-Chase experiment?

In the Hershey-Chase experiment, radioactive sulfur (³⁵S) and radioactive phosphorus (³²P) were used to label the protein and DNA of bacteriophages, respectively. Radioactive sulfur was incorporated into the protein coat, while radioactive phosphorus was incorporated into the DNA. During the infection of bacterial cells, the researchers observed that only the radioactive phosphorus entered the cells, indicating that DNA, not protein, is the genetic material.