DNA or Protein? A Recap of the Hershey-Chase Experiment

Looking for a summary of the Hershey-Chase experiments? Let's go!

Is protein or DNA the genetic material? To find out, Hershey and Chase used E. coli bacteria and the T2 bacteriophage. Key steps in the experiments included:

* 02:12 Using *radioactive isotopes* to label bacteriophage DNA and bacteriophage protein.
- Phages were cultured in medium containing EITHER sulfur-35 (35S) or phosphorus-32 (32P)
- Protein was labeled with Sulfur-35 (sulfur is present in protein but not DNA)
- DNA was labeled with Phosphorus-32 (phosphorus is present in DNA but not protein*)

* 03:58 *Infecting E. coli* with labeled phages - one batch of bacteria was infected with 35S phages (labeled protein), one batch was infected with 32P phages (labeled DNA)

* 04:46 Using a *blender* to shake off the phage ghosts from the infected bacteria

* 05:32 Using *centrifugation* to separate the bacteria from the rest of the mix (forming a pellet of bacterial cells)

* 06:27 *Detecting radiation*
- In the batch with 35S phages, radioactivity was found in the supernatant, indicating that phage proteins did NOT enter the bacterial cells during infection
- In the batch with 32P phages, radioactivity was found in the pellet, indicating that phages pass their DNA to bacteria during infection

*Conclusion: DNA, not protein, is the genetic material!*

This added even more evidence showing that DNA is the molecule of inheritance! Check out the Avery, Macleod, McCarty experiments for even more…

*Quick note about proteins and phosphorus – none of the 20 amino acids contain phosphorus, but after a protein is assembled, it can get some additional modifications to help it function or to make it active/inactive. Some proteins will have phosphorus added as part of this process – you may run into phosphorylation in your studies, so don’t panic if you see phosphorus in proteins later on :) Luckily, that wasn’t a problem for this study!

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