Section 12.1

*Identifying the substances in genes

*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

*Griffith’s Experiment

*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)

*Oswald Avery*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

*Hershey and Chase *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!

*Hershey and Chase

*The Role of DNA*Store information

*Copy information

*Transmit information