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THE DISCOVERY OF DNA
FUNCTION AND STRUCTURE
DNA FUNCTION
Griffith among the 1st scientists to conduct
research that would lead scientists to identifying
the material responsible for heredity.
Used bacteria to help solve this problem.
S-strain (virulent) - Coated with mucus and
caused pneumonia
R-strain (avirulent) - no mucus and did not
cause pneumonia
Griffith’s Experiment
Griffith’s Conclusion
These results led Griffith to believe that some
material from the S-strain was transferred to the
R-strain, which converted the R-strain to s-strain.
Transformation - the process during which bacteria
are changed by absorbing genetic material from an
outside source.
Griffith did not know what the transforming factor
was.
Avery, MacLeod, and McCarthy
• Separated cell components (protein, lipid,
carbohydrate, RNA, and DNA)
• Applied to culture of pneumoncoccus
• Identified DNA as transforming factor
Hershey-Chase
Chase and Hersey used bacteriophages
(phages) to prove whether protein or DNA is the
genetic material.
Hershey-Chase Experiment
1. Radioactive “hot” DNA was put in one group of phages
and radioactive “hot” protein was put into another group
of phages.
2. The “hot” phages were used to infect the bacteria.
3. Radioactivity was only found in bacteria infected by
DNA.
4. Confirmed DNA as the genetic material.
Contibutions leading to the discovery
of DNA Structure:
PA Levine
• Identified DNA is composed of:
a. phosphate group
b. 5-C sugar called deoxyribose
c. nitrogenous bases
1. Purines- adenine and guanine
2. Pyrimidines- thymine and cytosine
Nitrogenous Bases
The nitrogenous bases are divided into two groups.
Purines - include adenine
and guanine.
They have two rings.
Pyrimidines - include
cytosine and thymine.
They are smaller and
have only one
ring.
1949 Chargraff’s Rules
The amount of adenine in DNA is always equal to the
amount of thymine.
%A = %T
The amount of cytosine in DNA is always equal to the
amount of guanine.
%C = %G
Identified that the %ages A/T and G/C differed
between species.
1952 Rosalind Franklin and Maurice
• Kings College,
Wilkins
London
• X-Ray
Crystallography
• DNA made of
two strands that
run in opposite
directions
(antiparallel)
• Phosphate on
outside,
nitrogenous
bases on inside
Discover the Structure of DNA
The process by which DNA makes copies of itself
http://www.youtube.com/watch#v=teV62zrm2P0&fe
ature=related
1. Double helix unwinds
2. Hydrogen bonds are broken
3. The two strands break apart, like a zipper
4. New nucleotides begin to attach to the original DNA
5. This will form two new DNA molecules
This is semiconservative replication, because each new
strand is half comprised of molecules from the old strand.
DNA is a code (set of blueprints) for making protein.
Protein synthesis is the process that manufactures proteins.
RNA
Nucleic Acid
•Single stranded
•4 Bases
Adenine
Cytosine
•Ribose sugar
Guanine
Uracil