Hershey and Chase

DNA was discovered by Friedrich Miescher in 1869 and then in 1928, Griffith pointed out this material but was not able to recognize that material. This material was recognized by Avery, Mcleod, and McCarty in 1944.

But still, there was confusion about the hereditary material between DNA and protein. This confusion was removed by Hershey and Chase in 1952.

They performed their experiment on bacteriophages because they are very simple in structure (just protein coat and their genetic material).

They wanted to know, what is the hereditary material of new generations of bacteriophage.

Experiment on Bacteriophage.

They take radioactive isotopes of phosphorous32 and sulphur35.
They take some bacteriophages and some bacterial cells.
As bacteriophages are viruses that attack bacteria, they allow bacteriophages to attack bacteria.
But there was a twist in the story that they divided the bacterial cells into two halves in numbers.
The first half of bacterial cells were treated with radioactive sulfur 35.

Now, why do they do that?

They have done so because sulfur is present in protein and not in DNA. If protein is the hereditary material, then it will be found in new generations of bacteriophages.

The second half numbers of the bacterial cells were treated with radioactive phosphorous32.
They did this because phosphorous is the essential component of DNA and is not present in the protein.
If DNA is the hereditary material then it will be found in the next generations of bacteriophages.

Now the question is why they use radioactive materials.
The answer is for the easy detection of DNA and protein in the new generation. Radioactive material emits some kind of radiation so it is easy to detect them.

why Harshey and Chase use radioactive materials.

Now the first half numbers of bacterial cells were sulphur35 radioactive and the second half was phosphorous32 radioactive.
The bacteriophages were allowed to attack these two types of bacterial cells in different mediums.
Bacteriophage injects their genetic material inside these two different types of bacterial cells and starts to replicate their numbers by using bacterial reproductive machinery.

As we discussed earlier, if radioactive sulfur is found in the next generation of bacteriophage then the protein will be the hereditary material, and if radioactive phosphorous is found in the next generation of bacteriophage then DNA will be the hereditary material.

if genetic material was protein, then they will use sulfur radioactive material and thus found in the new generation of bacteriophage. While if the genetic material was DNA, then phosphorous32 will be found in new bacteriophage cells.

They take these newly formed bacteriophages and allow them to infect other normal bacterial cells.
They do so because the genetic material consists of radioactive elements and these radioactive were now ready to reproduce in new bacterial cells.
This will increase the concentration of these radioactive materials.
After some time, they separate the protein coat of bacteriophage from bacterial cells with the help of a blender.
They used a blender because it separates the empty shell of the bacteriophage (which attaches to the surface of a bacterial cell) and infectious or virulent material inside the cell of bacteria but makes a mixture of both protein coat and newly formed bacteriophages.
They take the mixture of empty protein coat of bacteriophages and infectious or virulent material from bacterial cells and place it in a centrifugal machine.
This machine moves this mixture at a very high speed and it will result in the separation of material according to their weight.
The heavy-weight cells of bacteriophage settle down while lightweight material (which is the empty coat of bacteriophage) floats on the surface.
They observed that phosphorous radioactive material was present in the new generation of bacteriophages.
So, they concluded that DNA is the genetic material that transfers from one generation to the next generation.