Experiments
Griffith's Experiment
Griffith determined that there was a transforming factor or a chemical responsible for change in the genetic makeup of an organism. In his experiment he had a strain of smooth, virulent bacteria and a strain of rough, non-virulent bacteria. As his control, he injected a mouse with the virulent strain -- it died. He injected another mouse with the non-virulent strain -- it lived. Then he took the virulent strain and used heat to kill it. He then injected a mouse with the killed virulent strain -- it lived. He injected another mouse with a killed virulent strain that had been mixed with a non-virulent strain -- it died. He concluded that something caused the genetic makeup of the non-virulent bacteria to change into something virulent.
Hershey-Chase Experiment
Hershey and Chase determined that it was DNA that controlled the cell's activities. In their experiment, they labeled a bacteriophage with radioactive sulfur (in the protein coat) and radioactive phosphorus (in the DNA). They then mixed the phage in with other bacteria and waited for infection to occur. Then, they scanned the bacteria for radioactive elements. Hershey and Chase discovered that the radioactive sulfur was discarded by the phages outside of the bacteria cells while the radioactive phosphorus was inside the infected bacterial cells. This led them to conclude that DNA that was the genetic material.
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