12.1: Identifying the Substance of Genes

 Investigating bacteria and pneumonia  S strain: mouse dies of pneumonia  R strain: mouse lives  Heat-killed S strain: mouse lives  Mix of heat-killed S strain and R strain: mouse dies  Conclusion: some chemical factor was transferred from dead S-strain to live R- strain cells (transformation). Offspring cells inherited the ability to cause disease  chemical factor had to be a gene

 Repeated Griffith’s work  Extracted molecules from heat-killed bacteria and treated it w/ enzymes that destroyed lipids, proteins, carbs, etc.  transformation still occurred  Repeated again but used enzymes that broke down nucleic acid (DNA)  transformation did not occur  Conclusion: DNA was the transforming factor

 Worked with bacteriophage (virus that infects bacteria) composed of DNA core and protein coat  Grew virus cultures that contained radioactive P-32 and S-35  Proteins contain no P; DNA contains no S  This will identify which molecule enters the bacteria carrying the genetic material  Result: all radioactivity in bacteria was from P, the marker found in DNA  Conclusion: Genetic material of bacteriophage was DNA, not protein

 Hershey and Chase’s experiment confirmed Avery’s findings—many scientists now convinced that DNA was the genetic material found in genes of all living cells

 Storing information  Genes control patterns of development  Genes carry the info to make a flower purple  Copy information  Before a cell divides it must make a complete copy of every one of its genes  Transmit information  DNA molecules must be carefully sorted and passed along during cell division