Chapter 12, Problem 10A

Summary Introduction

To Explain:

Use radioactive phosphorus to demonstrate that the transforming compound of bacteria in Griffith’s experiment was DNA.

Introduction:

Researchers discovered the factor responsible for the genetic inheritance patterns comes from within the organisms, but they fail to explain the hereditary material. Griffith’s experiment was stepped stone for the finding of genetic material.

Explanation of Solution

Griffith's six experiments followed to discover genetic material in organisms. But it was not accepted by all until Hershey and chase published their experimental results. Hershey and chase experiments applied to the Griffith experiment. In the experiment of Hershey and chase, take E.coli bacteria host for Bacteriophage to discover whether DNA or protein acts as the genetic material that enters into the bacteria.

The experiment starts with the culturing of the virus in two mediums. One set was radioactive labeled DNA by phosphorus, and the second set was radiolabeled protein by sulfur. This is because DNA contains phosphorus base compound while protein is not. The host for the infection was E.coli bacteria. The virus was allowed to infect bacteria by attachment and inserted genetic material, for the removal of the viral coat by numbers of blending and centrifugation. The radioactive and non-radioactive bacteria showed that the virus had radioactive label DNA transferred their DNA into bacteria. But the virus that contains non-radioactive protein does not transfer in bacteria. Therefore, DNA is a genetic material and not protein.

If we apply this to Griffith's experiment, we find the same results. Griffith took two strain which was S (smooth) live strain and R (rough) dead strain. S strain was lethal and R stain was non-lethal. When Griffith injected mice the non-virulent R strain, the mice survived. When mice injected with a virulent bacteria strain S, the mice died. When mice injected with heat-killed virulent bacterial strain R, mice survived. When infected mice with a mix of heat-killed strain S and living strain R, or the mice died.

Griffith concludes that the living R cells had something to be transformed into virulent S cells. It indicated that there was some form of transferrable genetic material present within the cell.

Conclusion

Therefore, if Griffith was applied S strain with phosphorus and R strain label with sulfur, then he will able to show that bacterial strain would contain the phosphorus labeled DNA. So he could explain that the transforming compound is DNA.