The Hershey and Chase Experiment | Discovery of DNA as the genetic material

Turning the Clock Back to the 1940s and 50s

In the 1940s and 50s, there was a debate in the scientific community about the nature of hereditary material. An experiment by Avery, MacCleod, and McCarty suggested that DNA, not proteins, was responsible for heredity. Alfred Hershey and Martha Chase conducted experiments to further investigate this question using a bacteriophage as a model organism.

The Nature of Hereditary Material

• Avery, MacCleod, and McCarty's experiment in 1944 challenged the prevailing belief that proteins were responsible for heredity.

• Not everyone was convinced by their results.

• Hershey and Chase needed a simple model organism to solve the complex question of whether DNA or protein was the hereditary material.

• They chose a bacteriophage, which is a virus that infects bacteria.

The Bacteriophage Experiment

• Bacteriophages attach to bacteria and inject substances into them to create new copies of the virus.

• The substance injected into bacteria contains the hereditary material.

• Hershey and Chase labeled one component of the virus with radioactive tags - radioactive phosphate for DNA and radioactive sulfur for protein.

• They used centrifugation to separate bacteria from viruses attached to their outsides.

• When they used virus with sulfur-labeled protein, most of the radioactivity remained with the virus and did not enter the bacteria. Protein was not being inherited.

• When they used virus with phosphate-labeled DNA, most of the radioactive DNA was injected into bacteria from attacking viruses. Labeled DNA was inherited by new generations of viruses.

Implications of Hershey-Chase Experiment

• Hershey and Chase's experiment provided evidence that DNA, not protein, was the molecule of heredity.

• Their experiments left some unanswered questions but helped convince many scientists of DNA's role in heredity.

• A year later, Watson and Crick published their model of the DNA double helix, further supporting the idea that DNA is responsible for passing on genetic information.

Conclusion

The experiments by Avery, MacCleod, McCarty, Hershey, and Chase played a crucial role in establishing DNA as the molecule of heredity. Watson and Crick's model of the DNA double helix provided an elegant explanation for how DNA can replicate and pass on information from parents to offspring.