explain the role of 35s and 32p in the experiments conducted by hershey and chase
To demonstrate that DNA is the genetic material, Hershey and Chase grew one culture of Escherichia coli in radioactive sulphur, 35S and the other culture in radioactive phosphorus 32P. Radioactive sulphur gets incorporated into sulphur containing amino acids and becomes part of bacterial proteins. Radioactive phosphorus gets incorporated into nucleotides which form nucleic acids, mostly DNA. Therefore, bacteria of both the cultures became labelled. Hershey and Chase then introduced bacteriophage T2 in both the bacterial cultures. The virus entered the bacteria where it multiplied. The viral progeny was tested in both the cases. It was labelled, one type with radioactive protein and other type with radioactive DNA. Each type of bacteriophage were now introduced in separate cultures having normal bacteria. After sometime both the cultures were gently shaken in a blender to remove the empty phage capsids sticking to the surface of bacteria. The culture was then centrifuged. The heavier bacteria settled down in the form of pellet whereas the supernatant contained lighter viral coats which do not enter the bacterial cells. Both the pellet and supernatant were analysed and it was found that phage with labelled protein did not make the bacteria labelled. Instead radioactivity was restricted to the supernatant which was found to contain only empty phage capsids. In the second culture where bacteriophage labelled with radioactive DNA was introduced, it was found that shaking did not produce any radioactivity in the supernatant having empty capsid coats. Instead, bacteria became labelled proving that only DNA of the phage entered the bacteria. The progeny of the two types of bacteriophages was again tested for radioactivity. Radioactivity was found to be absent in the viruses derived from parents having labelled protein. The viruses from parents having labelled DNA possessed radioactivity. This shows that genetic material is DNA and not the protein.