How did Hershey and chase show that DNA was the molecule that carried the genetic code?

Answer 1

Hershey (you know, Alfred Hershy) and Chase (you know again, Martha Chase) did some experiments with Bacteriophages (you know, viruses that affect Bacteria).

What they did in the experiment was that, they grew some of these Bacteriophages on a medium which contained radioactive Sulphus(S)(remember, radioactivity can be detected easily).

Then, they also took some other Bacteriophages. But, they were grown on radioactive Phosphorur(P).....

(Don't 4get(that's forget)), DNA also has Phosphorus in it (DNA = Nitrogen bases + Pentose sugar + Phosphorus).

Now, back to the experiment ------ The Bacteriophages that were grown on radioactive Phosphorus contained radioactive DNA. But they didn't have any radioactive protein coat. (remember viruses have a protein coat covering their DNA?)

Then, bacteriophages (please call them B from now, but not in the exams), which were grown in S (radioactive sulphur, remember?), had a radioactive protein coat (protien coats are made up of sulphur and some other elements), but no radioactive DNA........

That was the first part.......................

Now, the next one..........................

Radioactive B's, from both P and S were allowed to attach to E.coli (Esterichia coli) bacteria as an attack (or infection). After infection, The protein coats were removed by agitating (stirring real fast) in a blender (they're still not removed). Then, these virus particles (protein coats) wer removed by centrifugation (using centrifugal machine).

Then, the third big step....................................…

The observation part....................................…

It was observed that, some bacteria were radioactive and many were not. Also, it was observed that, bacteria which were attacked by B (Bacteriophage) having radioactive DNA were the ones which were radioactive..... Also that, bacteria which were attacked by B having S weren't radioactive......

So, it lead to the point that proteins didn't pass into bacteria, but it was the DNA that did......

So, DNA was concluded to be the genetic material......

Viruses were chosen because they only had genetic meterial & coat

This is from Yahoo anwsers btw

Answer 2

The primary factor is that DNA contains no sulfur and proteins contain no phosphorous. Thus, since the bacteriophage is just made of a protein capsid and DNA enclosed one can label either phosphorous or sulfur with their radioactive isotopes and preform the experiment ( easily found on line ) that differentiates DNA from proteins as the carrier of genetic information.