Explain the conclusions that were reached in the Hershey-chase Griffith and Avery experiments?

Answer 1

The Hershey-Chase experiments were a series of experiments conducted in 1952 by Alfred Hershey and Martha Chase, confirming that DNA was the genetic material, which had first been demonstrated in the 1944 Avery-MacLeod-McCarty experiment. While DNA had been known to biologists since 1869, most assumed at the time that proteins carried the information for inheritance.

Hershey and Chase conducted their experiments on the T2 phage, a virus whose structure had recently been shown by electron microscopy.The phage consists only of a protein shell containing its genetic material. The phage infects a bacterium by attaching to its outer membrane and injecting its genetic material, causing the bacterium's genetic machinery to produce more viruses, leaving its empty shell attached to the bacterium.Structural overview of T2 phage

In a first experiment, they labeled the DNA of phages with radioactive Phosphorus-32 (the element phosphorus is present in DNA but not present in any of the 20 amino acids from which proteins are made). They allowed the phages to infect E. coli, then removed the protein shells from the infected cells with a blender and separated the cells and viral coats by using a centrifuge. They found that the radioactive tracer was visible only in the pellet of bacterial cells and not in the supernatant containing the protein shells.

In a second experiment, they labeled the phages with radioactive Sulfur-35 (Sulfur is present in the amino acids cysteine and methionine, but not in DNA). After separation, the radioactive tracer then was found in the protein shells, but not in the infected bacteria, supporting the hypothesis that the genetic material which infects the bacteria is DNA.

Hershey shared the 1969 Nobel Prize in Physiology or Medicine for his "discoveries concerning the genetic structure of viruses."