KEY CONCEPT DNA was identified as the genetic material through a series of experiments.
Griffith finds a ‘transforming principle.’ Griffith experimented with the bacteria that cause pneumonia. He used two forms: the S form (deadly) and the R form (not deadly). A transforming material passed from dead S bacteria to live R bacteria, making them deadly.
Avery identified DNA as the transforming principle. Avery isolated and purified Griffith’s transforming principle. Avery performed three tests on the transforming principle. Qualitative tests showed DNA was present. Chemical tests showed the chemical makeup matched that of DNA. Enzyme tests showed only DNA-degrading enzymes stopped transformation.
Hershey and Chase confirm that DNA is the genetic material. Hershey and Chase studied viruses that infect bacteria, or bacteriophages. They tagged viral DNA with radioactive phosphorus. They tagged viral proteins with radioactive sulfur. Tagged DNA was found inside the bacteria; tagged proteins were not.
Which result of Frederick Griffith’s experiments led him to believe in a “transforming principle”? Mice injected with live S bacteria died. Mice injected with live R bacteria lived. Mice injected with dead S bacteria lived. Mice injected with dead S and live R bacteria died.
An important factor in Oswald Avery’s ability to identify the “transforming principle” as DNA was the fact that proteins Carry very little phosphorus. Were present in the extract made from S bacteria. Do not react with enzymes Could be observed in the extract made from R bacteria
Chemical analysis of Avery’s extracts showed that the ratio of nitrogen to phosphorus was consistent with that of Enzymes DNA Protein Bacteria
Hershey and Chase chose to use bacteriophages in their experiments because these viruses Contain little more than DNA and protein Can be seen with a light microscope Can infect only bacteria, not humans Will not grow in radioactive culture
As a result of Hershey and Chase experiments, scientists believe that Radioactive isotopes can be used safely Viruses use bacterial DNA to reproduce The “transforming principle” is DNA Bacteriophages can be grown in culture medium