Download DNA: The Genetic Material

Drill
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“All living things have me in them. Some
people call me the ‘code of life.’ I was
discovered in 1874. The amount of me in a
person’s body could stretch 13.5 times to the
Sun. In a chimpanzee, I am 98.5% similar to
that of a human. Who am I?”
DNA: The Genetic
Material
Section 12.1
Discovery of the Genetic Material
April 6, 2009
The Miraculous Acid
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In 1874, Friedrich Miescher
discovered acid molecules in
the nuclei of pus cells.
This acid became known as
deoxyribonucleic acid or DNA.
What is the genetic material?
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Frederick Griffith – British
microbiologist
In 1928, first to show that
bacteria are capable of
transferring genetic
information.
This became known as the
“transforming principle.”
Griffith’s Experiment
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Used two strains of Pneumococcus
bacteria:

 has
mucus coating.
 will cause fatal pneumonia in mice.
S strain

R- strain
S – strain
R – strain
 has
no coating.
 does not harm mice.
Griffith’s Experiment
Griffith’s Conclusion
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What? You want me to just tell
you…
Griffith did not know that the
“transforming principle” was
DNA.
Today we know that bacterial
cells have small circular
molecules of DNA called
plasmids that can be passed
between bacteria.
Oswald Avery
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Canadian physician and
bacteriologist
In 1944, with coworkers,
McCarty & MacLeod, he
discovered that the
“transforming principle” was
DNA.
Very cautious to report his
findings.
Avery, McCarty, & MacLeod, 1944

Repeated Griffith’s experiments with R- and
S-strain Pneumococcus bacteria.
1.
2.
Purified extracts of S-strain bacteria.
Treated extracts with protease – an enzyme
that destroys proteins

3.
Bacteria still transform.
Treated extracts with deoxyribonuclease – an
enzyme that eliminates DNA

No transformation.
Alfred Hershey & Martha Chase
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American geneticists
In 1952, identified
DNA to be the
genetic material of
phages – small
viruses that infect
bacteria -- and
ultimately, all
organisms.
The Blender Experiment
Section 12.1 Big Ideas

It took almost 80 years between
the discovery of DNA and
scientist’s understanding of its
significance.

Significant scientific discovery
results from the application of the
scientific method.
Section 12.1 Big Ideas

Science is often advanced by
the careful repetition, with
modification, of the
experiments of others.
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DNA is the genetic material of
all living organisms.
References:
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www.blc.arizona.edu/ INTERACTIVE/DNA3/DNA1.html
http://www.pbs.org/wgbh/nova/photo51/before.html
www.bio.davidson.edu/.../ Publicschedule.html
http://library.thinkquest.org/20465
http://www2.carthage.edu/~pfaffle/hgp/PF.html
http://en.wikipedia.org/wiki/Transforming_principle