The Hershey-Chase Experiment

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 bacterial Fage is 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 bacterial fage is to help them confirm that DNA was the genetic material. But what are these bacteria oaf? Ages? Well, bacteriophages are also sometimes referred to as just Fage is, and so bacteria pages and pages 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, uh, a representation of what a bacteria fage actually looks like. And it's this pink structure that you see here and typically these bacteria phases they consist of an external protein coat and this external protein coat is going to be surrounding a nuke Laich acid core in the center. And so what you can see here in our images Uh, this bacterial fage 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 new Clague acid core. And so the new clinic acid here would represent DNA here in this scenario. And, of course, what these bacteriophages do is they in fact, bacterial cells and so you can see that are bacterial cells being shown down below? Here and now today we know that the way that bacteriophages operate is they inject the new click acid into the bacterial cell. But at the time in the 19 fifties, they were not sure exactly how these bacterial Fage is operated. Some scientists thought that perhaps it's the protein that actually makes its way into the bacterial cell on dso this her she chased experiment is the one that really revealed how the bacteria phages worked and the, um, that revelation of how bacteriophages work helped to confirm that DNA is the genetic material. But 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 they use bacteria pages and again, I'll see you in our next video to turn toe, learn more.

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 take away that you should get of this Hershey Chase experiment is that the scientists Hershey and Chase were able to show that Onley viral DNA and not viral protein actually enters the bacteria during a bacteria fage infection. And the fact that Onley viral DNA and not viral protein enters bacteria during a bacterial fage 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 bacteria. Fage is okay, and they took multiple bacteriophages and separated them into two groups. They had the group over here on the left hand side and the other group of bacteria pages over here on the right hand side. Now on the left hand side, they took the bacteria pages, and they used radioactive sulfur labels. Toe label the viral protein coat that's on the external of the bacterial fage on. 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 bacteria pages, and they used radioactive phosphorus labels instead of radioactive sulfur labels and the radioactive phosphorus labels with label the viral DNA. And so notice that it's on Lee the viral DNA that's highlighted here in yellow. That's at the core of the bacteria Fiege. 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 bacteria phage 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. Uh, what they saw was that the radioactively labeled viral DNA was actually found on the inside on the inside of the cell. And the fact that this radioactively labeled DNA was found on the inside was evident to suggest and confirmed that it was the viral DNA that acted and served as the genetic material. And so, once again, the biggest take away 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. And so this year 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.