Hershey and Chase (1952)
Basic concept
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Detailed Explanation...
- Alfred Hershey and Martha Chase studied a virus named T2, this virus infects bacterial cells, in this case E.coli.
- T2 phage coat has outer covering called phage coat, that contains a head (capsid), sheath, tail fibres and base plate. Phage coat is composed entirely of protein. DNA is found inside the head of T2.
- To replicate, all viruses must introduce genetic material into the cytoplasm of a living host cell
- In the case of T2, this involves attached of its tail fibres to the bacterial cell wall and the injection of its genetic material into the cytoplasm
- BUT, at the time of Hershey and Chase's work, it was not known whether the phage was injecting DNA or protein, whether DNA or protein was the genetic material.
- Hershey and Chase carried out an investigation to find out this
- They devised a method to separate the phage coat (attached outside of bacterium) from the genetic material (which is injected into cytoplasm)
- They said that the attachment of T2 on the surface of bacterium can be disrupted if cells were subject to high shear forces (such as those produced by a blender)
- To distinguish T2 protein and DNA, they used radioisotopes as a way to label these mol
- Sulphur atoms found in protein not in DNA and phosphorous atoms found in DNA not in phage protein
- They therefore exposed T2 to (35S) or to (32P)
- These infected cells produced phages that had incorportaed (35S) into their protein and (32P) into their DNA.
Steps of the Experiment
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Detailed Picture Explaining the Hershey-Chase Experiment