Part 1
Discovery of DNA & its structure
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Learning Target
2. Know the contributions of
Griffin
Avery-MacLeod-McCarty
Hershey-Chase.
Watson and Crick
Franklin
Chargaff
……make a timeline……
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Griffith & Bacterial Transformation
• 1928- Frederick Griffith
• Studied 2 strains of
pneumonia from mice
• 1 caused pneumonia
• 1 did not cause
pneumonia
• Non-pneumonia kind
was “transformed” into
pneumonia kind
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Avery-MacLeod-McCarty
• 1944—Oswald Avery
• They used process of elimination to
determine which molecule gets
transferred
• DNA was the molecule being
transferred from 1 bacteria to another
in Griffith’s experiment
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Hershey & Chase
• 1952—Alfred Hershey & Martha
Chase
• Studied bacteriophages
• Bacteria killing viruses
• Attached radioactive markers to
proteins and to DNA to see
which one was genetic material
• Determined that DNA, not
protein functions as genetic
material
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Phage
head
Tail
Tail fiber
Bacterial
cell
100 nm
DNA
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Other clues to DNA’s Structure:
Chargaff
• Erwin Chargaff (American
biochemist) 1950
• “Chargaff’s Rules”
• Species have different amounts of A,
T, G & C
• Analyzed amounts of Adenine,
cytosine, guanine & thymine
• Amount of A = T
• Amount of C = G
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Wilkins & Franklin
• Early 1950’s– Maurice Wilkins &
Rosalind Franklin
• From images captured through X-ray
crystallographers
•
•
•
•
Maybe a “twisted” structure
Maybe a helix
Maybe 2 strands
Maybe nitrogen bases in
middle
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Rosalind Franklin and her X-ray diffraction photo of DNA
(a) Rosalind Franklin
(b) Franklin’s X-ray diffraction
Photograph of DNA
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Watson & Crick
• James Watson (American
biologist)
• Francis Crick (British physicist)
• 1953  put all the clues
together
• Built wire/tin model
• “Double Helix”
• Nobel Prize 1962
• Watson, Crick, Wilkins
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