The Hershey-Chase Experiment - Video Tutorials & Practice Problems
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1
concept
Bacteriophages
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Video transcript
In this video, we're going to begin our lesson on the Hershey Chase experiment. And so what's important to recall from our previous lesson videos is that even after the Griffith experiment and subsequent experiments that 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. And it wasn't until 1952 when the scientists Alfred Hershey and Martha Chase used bacteriophages in order 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. And so again, Hershey and Chase, they 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. And so bacteriophages and phages are the same thing. And really what they are, they are a virus that replicates itself by infecting and hijacking bacteria. And so down 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. And typically these bacteriophages, they consist of an external protein coat. And, this external protein coat is going to be surrounding a nucleic acid core in the center. And so what you can see here in our image is, this bacteriophage that you see here consists of an external protein coat that you can see here. And within this external protein coat, you can see that on the inside is the nucleic acid core. And so, the nucleic acid here would represent DNA here in this scenario. And, of course, what these bacteriophages do is they infect bacterial cells. And so you can see that our bacterial cell is being shown down below here. And, now today, we know that the way that bacteriophages operate is they inject the nucleic acid into the bacterial cell. But at the time in 19 fifties, 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. And so, this Hershey Chase experiment is the one that really revealed how the bacteriophages worked. And the, that revelation of how bacteriophages work helped to confirm that DNA is the genetic material. But we're gonna 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 they use bacteriophages. And again, I'll see you in our next video to turn to learn more.
2
concept
The Hershey-Chase Experiment
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Video transcript
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 of 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 code, 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 And the And the fact that this 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 of the Hershey 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.
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Problem
Problem
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.
4
Problem
Problem
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.
5
Problem
Problem
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.