Section 12.1

* 1928 British scientist – Frederick Griffith * Wanted to know how bacteria made people sick, especially pneumonia * Griffith isolated 2 types of pneumonia bacteria: * S strain – harmful bacteria, smooth edges * R strain – harmless bacteria, rough edges

* WHAT HAPPENED??? * Somehow the heat killed bacteria passed the ability to cause disease to the harmless strain of bacteria * Transformation = one type of bacteria (harmless) had been permanently changed into another (harmful)

* 1944 Canadian scientist Oswald Avery * Wanted to determine which molecule in the heat-killed bacteria was most important for transformation * EXPERIMENT * Extracted a mixture of various molecules from the heat killed bacteria. * They treated the mixture with enzymes that destroyed proteins, lipids, carbohydrates, and nucleic acids * RESULTS * Transformation still occurred * None of the molecules mentioned above could have been responsible since they were destroyed * Except…. When DNA was destroyed. Transformation could NOT occur

* Studied Viruses, more specifically bacteriophages (virus that infects bacteria) * They wanted to know which part of the virus – the protein coat or the DNA core – entered the bacterial cell * EXPERIMENT * Grew cultures of viruses in radioactive isotopes * DNA was marked with phosphorus * Protein was marked with sulfur * RESULTS * Genetic material of the bacteriophage was DNA and not protein * They convinced other scientists that DNA was the genetic material found in genes in all living things!

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