Discovery of DNA
Discovery of DNA
● DNA=
deoxyribonucleic
acid
● 3 major experiments
determined that
DNA was the body’s
genetic material
Frederick Griffith
● 1928
● Found that the bacteria
Streptococcus pneumoniae was
the cause of pneumonia
● The bacteria comes in 2 forms
○ rough
○ smooth
Frederick Griffith
● Mice injected with...
○ smooth bacteria
died of pneumonia
within days
○ rough bacteria
lived
Frederick Griffith
● Mice injected with...
○ heat-killed smooth
bacteria lived
○ heat-killed smooth
and living rough
bacteria died
Frederick Griffith
● Found living smooth bacteria in the dead
smooth and living rough sample
● Conclusion: There was a “transforming
principle” that turned rough bacteria into
the deadly smooth type
Oswald Avery
● 1944
● Continued Griffith’s work
○ Took heat-killed smooth
bacteria and destroyed its
proteins, lipids, and carbs with
enzymes
○ Still made rough bacteria deadly
Oswald Avery
● Continued Griffith’s work
○ Took heat-killed smooth bacteria and
destroyed its DNA
○ Rough bacteria did not become deadly
● Conclusion: DNA stores the genetic
material in a cell
Alfred Hershey & Martha Chase
● 1952
● Studied
bacteriophages
(viruses that infect
bacteria) to see if
genes were
protein or DNA
Alfred Hershey & Martha Chase
● Added radioactive
phosphorus to the DNA
(proteins don’t contain
phosphorus)
● Added radioactive sulfur
to the proteins (DNA
doesn’t contain sulfur)
Alfred Hershey & Martha Chase
● They let the virus infect
the bacteria and checked
to see which radioactive
element was in the cell
● They found phosphorus
but not sulfur inside
Alfred Hershey & Martha Chase
● Conclusion: Genes are
made of DNA and not
proteins