Experiments of Frederick Griffith

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Experiments of Frederick Griffith
Frederick Griffith with his dog Bobby
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Experiments of Frederick Griffith 1st step
bacteria reproduce inside mouse
injected into
R strain
mouse lives
bacteria reproduce inside mouse
injected into
S strain
mouse dies
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Experiments of Frederick Griffith 2nd step
S strain
no bacteria reproduce inside mouse
injected into
dead bacterium
mouse lives
add heat
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Experiments of Frederick Griffith 3rd step
bacteria reproduce inside mouse
R strain
S strain
injected into
mouse dies
dead
alive
live R with dead S DNA
Conclusion the R strain was transformed into a
deadly S strain
Griffith called this a transformation.
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Experiments of Oswald Avery
Oswald Avery expanded on the experiments of
Frederick Griffith.
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Experiments of Oswald Avery 1st step
S strain
dead
extract (containing cell molecules)
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Experiments of Oswald Avery 2nd step
bacteria reproduce inside mouse
R strain
protein destroying enzymes
mouse dies
alive
extract
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Experiments of Oswald Avery 3rd step
bacteria reproduce inside mouse
R strain
DNA destroying enzymes
mouse lives
alive
extract
Conclusion DNA is the transforming compound.
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Experiments of Alfred Hershey Martha Chase
Using Radioactive Markers to Confirm Averys Work
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Alfred Hershey Martha Chase 1st step
Bacteriophage (viruses that infect bacteria) were
grown with radioactive sulfur.
Bacteriophage
Bacteriophage
DNA
DNA
35
S
Radioactive Virus
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Alfred Hershey Martha Chase 2nd step
DNA
no radioactivity
Radioactive Virus with S
35
Protein contains sulfur no radioactive sulfur
was found in the bacteria.
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Alfred Hershey Martha Chase 3rd step
Bacteriophage were grown with radioactive
phosphorus.
Bacteriophage
Bacteriophage
DNA
DNA
32
P
Radioactive Virus
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Alfred Hershey Martha Chase 4th step
DNA
radioactivity
Radioactive Virus with P
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DNA contains phosphorus radioactive phosphorus
was found in the bacteria.
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Alfred Hershey Martha Chase Conclusion
DNA, not protein, is the genetic material!
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Work of Erwin Chargaff
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Work of Erwin Chargaff
Chargaff found that for any sample of DNA, the
concentration of adenine always equals the
concentration of thymine, and the concentration
of guanine always equals the concentration of
cytosine.
Chargaffs Rule
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So if 36 What would the be?
What would the be?
What would the be?
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Work of Rosalind Franklin
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Work of Rosalind Franklin
Franklin took X-ray pictures of different
compounds. When she took this one of DNA, she
realized it showed that DNA was a double helix.
DNA - a double helix
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Work of James Watson Francis Crick
Watson Crick, after getting the data from
Franklin using Chargaffs Rule, were able to
construct the 1st accurate model of DNA
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Work of James Watson Francis Crick
They found that one side of the molecule was
bonded to the other side with hydrogen bonds.