Transcript Griffith`s Experiments

Identifying the Genetic Material
 Relate Griffith’s conclusions to the
observations he made during the
transformation experiments.
 Summarize the steps involved in Avery’s
transformation experiments, and state the
results.
 Evaluate the results of the Hershey and
Chase experiment.
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Griffith’s Experiments
 In 1928, Frederick Griffith, a
bacteriologist, trying to make a vaccine
against pneumonia.
 A vaccine is prepared from killed or
weakened disease-causing agents,
including bacteria.
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discovered harmless bacteria
turn virulent when mixed
with disease causing bacteria.
A bacteria that is virulent is
able to cause disease.
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 Griffith
discovered what is
now called transformation a change in genotype when
cells take up foreign genetic
material.
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Avery’s Experiments
 In 1944, the material responsible for
transformation is not affected by proteindestroying enzymes. The activity is
stopped, however, by a DNA-destroying
enzyme.
 100 years after Mendel’s experiments,
Avery demonstrated that DNA is the
material responsible for transformation.
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DNA’s Role Revealed
 In 1952, Alfred Hershey and Martha Chase used
the bacteriophage T2 to prove that DNA carried
genetic material.
 A bacteriophage, is a virus that infects bacteria.
 When phages infect bacterial cells, the phages
are able to produce more viruses, which are
released when the bacterial cells rupture.
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http://www.cellsalive.com/phage.htm
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DNA’s Role Revealed
• Hershey and Chase concluded
that the DNA of viruses is
injected into the bacterial cells,
while most of the viral proteins
remain outside.
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 The
injected DNA molecules
causes the bacterial cells to
produce more viral DNA and
proteins.
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How does environment affect your
DNA?
http://www.pbs.org/wgbh/nova/sciencenow/3411/02.html
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