4. Hershey and Chase experiment

Hershey and Chase in their experiments used the T2 bacteriophage as the vehicle for delivering genetic material. Like all bacterial viruses, T2 is comprised of only a protein-based outer wall and a DNA core, its simple structure making it the perfect research candidate. The virus protein contains sulfur but no phosphorus and the virus DNA contains phosphorus but no sulfur. They tagged the T2 phage DNA with radioactive phosphorous (P³²) and proteins with radioactive sulfur (S³⁵).  The researchers could track the location of DNA and protein according to the radiation concentrations. Then they allowed the tagged phages for infection to E.coli. After introducing phage culture to the bacterial sample, it was agitated in blender to brutally disturb the infected bacteria, causing the protein shells to detach from their hosts. Then, for separation of bacterium from the phages and proteins, they used a centrifuge. Once the separation was complete, they measured the radiation concentrations in the E.coli cells and the protein shells. The most of the P³² label appeared in large quantities within the bacterial sample, demonstrating that DNA was transferred from the bacteriophage to the host organism whereas most of the S³⁵ label had remained outside of the cells. Further, despite the protein shells were detached, reproduction of the phage was taking place and the virus was still copied in each of the host cells. This, suggested that the proteins shell itself was not necessary to the replication process following the initial insertion of genetic material Figure 21.3.

 

Figure 21.3: Hersey and Chase's experiment with T2 Bacteriophase in E. coili

So from previous explanation we can define the genetic material “The genetic material of a cell or a plant refers to those materials found in the nucleus, mitochondria and chloroplast, which play a fundamental role in determining the structure and nature of cell substances, and capable of self-propagating and variation. It can be a gene, a part of a gene, a group of genes, a DNA molecule, a fragment of DNA, a group of DNA molecules, or the entire genome of an organism.”