Question

‘DNA is a genetic material’. Prove it with the help of the Hershey-Chase experiment. Draw a linear diagram of the experiment.

Answer 1

Hint: DNA is abbreviated for Deoxy-ribose nucleic acid. It is a genetic material as it passes down the information from one organism to another. Hershey-Chase experimented with the bacteriophage virus. The virus helped in determining whether the protein of the DNA contained the genetic information.

Complete step by step answer: Hershey-Chase experiment: The experiments of Alfred Hershey and Martha Chase in 1952 gave unambiguous proof that DNA is the genetic material. They experimented with the Bacteriophages. The T2 bacteriophage is the virus that infects E. coli and multiplies within it. The T2 bacteriophage consists of only the protein coat and the DNA. Thus, it is the most suitable agent to determine the nature of the genetic material.
-The functions of the DNA and the proteins are determined by labeling them with the radioactive tracers. The DNA is made up of phosphorus and the proteins are made up of sulfur. On the other hand, the DNA does not contain sulfur and the proteins do not contain phosphorus. Therefore, the DNA of the bacteriophage was labeled with the radioactive isotope of Phosphorus-32 by growing the E. coli bacteria that were infected with the phage virus in the culture medium of phosphate having radioactive Phosphorus-32. The protein coat of the bacteriophage was labeled with the radioactive isotope of Sulfur-35 by growing the E. coli bacteria that were infected with the phage virus in the culture medium of sulfate having radioactive Sulfur-35. After this, the following three steps were followed –
1. Infection - Both the types of the labeled bacteriophages were made to infect the normally cultured bacteria in two separate dishes.
2. Blending - These infected bacterial cells are then agitated in the blender so that the contact between the virus and the bacteria can be broken.
3. Centrifugation - The virus and the bacteria are separated by the centrifugation process.
After the centrifugation, it was observed that the bacterial cells showed the presence of the radioactive DNA labeled with Phosphorus-32. The radioactive protein labeled with the Sulfur-35 was seen in the medium. Also, the labeled DNA was found in the next generation of the bacteriophages. On the other hand, the bacteria that were labeled with the radioactive proteins were not radioactive. This indicated that the proteins did not enter the bacteria from the viruses. Therefore, it was concluded that the DNA was the genetic material.

Note: Before Hershey and Chase, Griffith had already given his transformation principle. He already stated that there were some genetic materials that were getting transferred from one generation to another. However, the biochemical nature of this genetic material was not established from his experiments. Three scientists named Oswald Avery, Colin Macleod, and Maclyn McCarty established the biochemical nature of the genetic material of Griffith. They proved that the genetic material was DNA however, their experiments were rejected since other biologists were not convinced with them. Finally, Hershey and Chase proved that DNA is the genetic material.