Discovery of DNA
Griffith’s Conclusion: “something”
transformed the harmless bacteria into
the deadly bacteria. (He called this
process transformation)
Oswald Avery – repeated Griffith’s work
to determine which molecule was
responsible for transformation
• Conclusion: DNA was the
transforming factor that caused the
change in the R-strain
Discovery of DNA
Alfred Hershey & Martha Chase
• Question: Are genes made of DNA or
proteins?
• What they knew:
 viruses use other organisms to
reproduce
 Viruses only contain DNA and a
protein coat.
 Whichever virus particle enters the
cell must be the material that makes
up genes (DNA).
• https://www.youtube.com/watch?v=iLx_Uz
_xiAQ
Discovery of DNA
http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/
0072437316/120076/bio21.swf::Hershey%20and%20Chase%20E
xperiment
Hershey and Chase
• Experiment:
– They tagged the virus DNA
with blue radioactive
phosphorous
– They tagged the protein coat
with red radioactive sulfur
• Results:
– the cells only contained blue
radioactive phosphorous.
• Conclusion:
– Virus only injects DNA
(confirms Avery’s results)