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1 What Is
the Evidence that the Gene Is DNA?
In 1920s, WHO , working with
two strains of Streptococcus pneumoniae determined that a transforming
principle from dead cells of one strain produced a heritable change in the
other strain.
Frederick Griffith
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What Is the
Evidence that the Gene Is DNA?
To identify the transforming principle:
WHO treated samples to destroy
different molecules;
• If DNA was
destroyed, the transforming activity was lost.
• There was no loss of activity with destruction of
proteins, carbohydrates, or lipids.
Averey
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•
In 1952, WHO
confirmed DNA is the genetic material
–
T2 bacteriophage (virus that attacks
bacteria) consists of DNA core packed in protein coat
Hershey and Chase
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• Used bacteriophage T2 virus to determine whether DNA, or
protein, is the genetic material
• Bacteriophage proteins were labeled with 35S;
the DNA was labeled with 32P
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Experiment
(Part 2)
13.1 What Is
the Evidence that the Gene Is DNA?
Genetic transformation of eukaryotic cells, transfection,
can be demonstrated.
• A genetic marker—a gene that confers an observable
phenotype—is used.
Any cell can be transfected, even an egg
cell—result is a transgenic organism
Hershey–Chase
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1950s What Is
the Structure of DNA?
• The structure of DNA was determined using many lines of
evidence.
One crucial piece came from X-ray
crystallography from chemists
Wilkins and Franklin
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What Is the
Structure of DNA?
Chemical composition also provided clues:
DNA is a polymer of nucleotides: Deoxyribose,
a phosphate group, and a nitrogen-containing base.
Wilkins and Franklin
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What
Is the Structure of DNA?
Purines: adenine (A), guanine (G)
Pyrimidines: cytosine (C), thymine (T)
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2 What Is
the Structure of DNA?
Model building started by Linus
Pauling—building 3-D models of possible molecular structures.
WHO used model
building and combined all the knowledge of DNA to determine its structure.
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