The Hammerling Experiment The Hammerling Experiment

9/2/2015
Targets:
DNA
To review the process that lead to discovering that DNA
was responsible for the genetic information in the cell
The Discovery of Genetic Material
BIOLOGY 12
2 SEPTEMBER 2015
The Genetic Mystery:
It had become evident that information could be
passed from one generation to the next
The search began to try and find out what part of
the cell was responsible and how this was
accomplished
The Hammerling
Experiment
He then took two species of
Acetabularia:
He then cut the caps off each
sample and switched a part of the
stalk from one species to the other
If his theory was correct, regardless
of what species the stalk was from,
the top would be determined by
the species of the foot
A. mediterranea and A. Crenulata
The Hammerling
Experiment
The big question: Where is genetic
information stored?
Danish biologist Joachim Hammerling
(1930) cut cells into pieces and observed
the pieces to see which were able to
express hereditary information
He used a form of green algae
(Acetabularia) and amputated the caps
to which he found they simply regrew.
When the foot of the plant was cut, no
new foot grew.
He concluded that the hereditary
information residedinthe foot of
Acetabularia
What did he
find?
Immediately
after the
transplant the
cap that
regrew
resembled
the cap of
the
transplanted
stalk
All
Generations
after this saw
the cap that
matched the
base’s
species.
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9/2/2015
The Hammerling
Experiment
The Griffith Experiment
It became clear that there was something in the
nucleus of the cell that was able to pass information
from one cell to another
Frederick Griffith (1928) made observations on mice
when infecting them with different strains of the
steptococcus pneumoniae bacteria
Conclusion
It was shown through the experiments with
Acetabularia that the hereditary information was
stored in the nucleus of the cells in the foot
This lead biologists to realize that the nucleus is
where they needed to focus
The Griffith Experiment
(1) He infects
healthy mice
with a
pathogenic
(disease
causing) strain
of
S.pneumoniae
- The mice die
(2) He infects mice
with a
nonpathogenic
strain of the
bacteria (a
mutant form)
- The mice Live
The Griffith Experiment
(3) Killing the virus
first to see if
the virus
structure itself
was toxic
- The Mice Live
(4) Finally he mixes
dead
pathogenic
virus with live
nonpathogenic
virus.
- Expected
Mice to live
-Mice Died
The Griffith Experiment
The Avery Experiment
The agent responsible for the transformation of the
bacteria in the Griffith experiment was unknown
until 1944
Oswald Avery conducted an experiment:
Conclusion:
Somehow the information that made the virus
deadly was passed from the dead pathogenic virus
to the living nonpathogenic virus
Genetic information can be passed from dead cells
to living ones, transforming them (A process known
as transformation)
A mixture of viruses similar to what was used in the
Griffith Experiment was used (Live nonpathogenic
and dead Pathogenic S. Streptococcus)
Almost all (99.98%) of the protein was removed from
the virus and the mice were infected again
The mice died. The lower protein had little effect
The only material left that could be responsible
was DNA (Deoxyribonucleic Acid)
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The Hershey-Chase
Experiment
The Avery Experiment’s conclusion that DNA was
responsible for information transmission was not
accepted at first
Additional Evidence would be provided in 1952
The Hershey-Chase
Experiment
This side
will track
the
Sulfur in
the
Protein
Coat
This side will
track the
phosphorus
in the DNA
It was widely believed that protein, not DNA, was
responsible for passing information from one
generation to the next.
Alfred Hershey and Martha Chase conducted an
experiment that would settle the argument
The Hershey-Chase
Experiment
Conclusion:
The Phosphorus (32P) was found in the bacteria, not
the sulfur (35S)
This settles the debate: DNA is definitely what
passes information between generations
https://www.youtube.com/watch?v=BXhFDh15hhg
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