Chapter 12: DNA and RNA

12-1: Discovering DNA Frederick Griffith (1928) tried to find better ways to fight pneumonia isolated 2 types of bacteria that cause pneumonia smooth: deadly form rough: nondeadly form

Griffith’s Experiment R-strain (Rough): Nonvirulent S-strain (Smooth): Virulent Heat Killed S-Strain: Nonvirulent R-strain + Heat Killed S-strain: ???

Griffith’s Results

What killed the mouse? Why did the R-strain and heat killed S-strain combination kill the mouse?

Transformation when one type of bacteria is changed into another realized some molecule changed harmless rough bacteria into deadly smooth bacteria

Oswald Avery (1944) wanted to find out which molecule caused transformation found transformation was blocked when DNA was destroyed concluded genes are made up of DNA

DNA is the Transforming Factor Avery’s Experiment Treated the R-strain and heat killed S-strain bacteria with enzymes designed to destroy proteins and DNA. Proteins were destroyed → mouse died DNA was destroyed → mouse lived

Hershey and Chase (1952) used radioactive isotopes used bacteriophages: type of virus that infects bacteria contains protein and DNA

Hershey and Chase

Hershey and Chase’s Results used radioactive isotopes to label the DNA and protein in a bacteriophage labeled DNA with phosphorus-32 labeled protein with sulfur-35 allowed bacteriophage to infect a bacterium found bacterium was made radioactive by phosphorus-32 concluded genetic material of bacteriophage must be DNA

Hershey and Chase Animation http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120076/bio21.swf::Hershey%20and%20Chase%20Experiment