Chapter 12: DNA
Deoxyribonucleic Acid
Section 1:
Identifying the Substance of Genes
J. Friedrich Miescher
Studied white blood cells (leukocytes)
Discovered DNA during process
in1869
Actually named it “nuclein” later
renamed to DNA for acidic
properties
Discovery of DNA
Frederick Griffith
• Studied bacteria that caused
pneumonia
• He figured out that you
could change one strain of
Scientists knew that
bacteria into another strain
people had different
of bacteria –
traits because they had
transformation
different genes.
Scientists did not know
what type of molecule
made up our genes.
Griffith’s Experiment
Two Strains of Bacteria
R strain - Harmless
S strain – Deadly
Discovery of DNA
Explain the results of Griffith’s experiment. Why
did mouse 4 die?
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