Transcript Slide 1

Who: Frederick Griffith
When: 1928
What did they do: Experimented with
mice using 2 strains of pneumonia bacteria
(one harmful and one harmless)
He killed the harmful strain by heating it
and mixed it with the harmless strain;
Harmless bacteria “transformed” into
harmful bacteria & killed mice
Who: Oswald Avery (and McCarty & MacLeod)
When: 1944
What did they do:
Repeated Griffith’s experiments
Wanted to find the “transforming factor”, (Is
it the protein or the DNA?)
Protein + DNA = Transformed
DNA + no Protein = Transformed
Protein + no DNA = Not transformed
Realized DNA is the transformation factor.
Who: Erwin Chargaff
When: 1950
What did he do:
Found that the bases adenine and
thymine always pair together and
cytosine and guanine always pair
together
Chargaffs Rule:
A pairs with T
C pairs with G
Who: Rosalind Franklin and Maurice
Wilkins
When: 1951
What did they do:
Used x-ray crystallography to take
pictures of DNA and discovered the
shape (double stranded and twisted like a
helix)
Who: Alfred Hershey and Martha Chase
When: 1952
What did they do:
Conducted “Blender experiment” with 2
sets of bacteriophages
Proved that genes are made up of the
nucleic acid DNA
Concluded that DNA must be the
genetic material
Who: James Watson and Francis Crick
When: 1953
What did they do:
Took all the information that the other
scientists gathered and put together the
first complete model of DNA
Won the Nobel Prize for this
accomplishment