Comparing Baker's Toughest Experiments

There were 3 main experiments that were conducted in the 19th century. The first experiment was conducted in 1928 by Frederick Griffiths. He was able to establish that there is a substance being transmitted from one generation to another. For this experiment Griffiths used two types of pneumococcus bacteria (the bacteria that is responsible for causing pneumonia). He used the smooth strain (S) which had an outer capsule that acts as a protective shield from the host’s immune system and rough strain (R) which lacked the capsule. He then injected the S-strain bacteria into the mouse, as a result the mouse died due to the s-strain infecting it with pneumonia. When the r-strain was injected into the mouse, the mouse was able to survive the infection
It was conducted in 1944 by Oswald Avery, Colin MacLeod and Maclyn McCarthy. The purpose of this experiment was to prove that the heritable substance found by Griffiths was actually DNA. They considered protein, RNA and DNA to be the possible substance, so they used the process of elimination. For this experiment, they used the mixture of the s-strain and r-strain and combined it with protease (to remove the protein) and injected it into the mouse. In this case the mouse ended up dead, this is due to the hereditary component still being present. Therefore protein is excluded. They did the same for RNA by using RNase, which resulted in the mouse dying. When the s-strain and r0strain were combined with DNase and injected into the rat, the rat ended up alive. This meant that the heritable substance has been removed, because the s-strain was unable to transform the r-strain into the s-strain therefore the mouse’s immune system was able to fight off the bacteria. Henceforth, Avery, MacLeod and McCarty were able to conclude that DNA is the heritable substance (discovered by Griffiths) responsible for the transformation of the r-strain into the
For this experiment, Bacteriophage T2 (a virus that infects bacteria) and radioactive isotopes of Sulfur and Phosphorous (35S and 32P). 2 Batches were created where one was of the sulfur and the other was of the phosphorous. In batch 1, the bacteriophage was cultured in the presence of the Sulfur isotpe, this resulted in a radioactive protein coat of the bacteriophage. In batch 2, the bacteriophage was cultured in the presence of the phosphorous isotope, this then resulted in the DNA of the bacteriophage being radioactive. They then took these new radioactive bacteriophages and mixed them with E.coli (bacteria) in a Waring blender. In batch 1, the bacteriophage emptied its DNA into the bacteria leaving the radioactive protein coat. In batch 2, the radioactive DNA ended up in the bacteria. They used a centrifuge to completely separate the bacteriophage and protein coat from the bacteria. Once the separation was complete, they measured radioactivity in each of the batches. In batch 1 radioactivity was present in the protein coat, but not in the protein of the offspring’s. In batch 2 the radioactivity was present in the DNA of the offspring’s of the bacteriophages. These findings resulted in Hershey and Chase concluding that indeed DNA and not protein was responsible for creating a new