1. DNA
Discovery that DNA, not Protein is Genetic Material
Fredrick Griffith
Oswald Avery
Hershey and Chase
Erwin Chargaff
Rosalind Franklin
Watson and Crick
DNA Structure
Nucleotides
Nitrogen Bases
Base-Pairing Rule
DNA Replication
Helicase
DNA Polymerase
Result

2. Unit IV
Learning Goal 3
DESCRIBE THE STRUCTURE OF DNA, ITS
DISCOVERY, AND ITS IMPORTANCE IN DNA
REPLICATION.

3. Discovery that DNA not Protein is
Genetic Material
Frederick Griffith
(1928)
 Heat killed
pneumonia bacteria
could transform
harmless bacteria into
bacteria that caused
pneumonia.

4. Avery’s World
 Pneumonia leading
cause of death in
America, early 1900’s.
 50,000 deaths/year.
 During World War I
called the “Captain of
Death” in hospitals.
http://www.nlm.nih.gov/
http://www.who.int/mediacentre/factsheets/fs331/en/index.html

5. Oswald Avery (1944)
Discovered that nucleic
acids were the only
molecules that could
transform bacteria.
 DNA not RNA was
responsible for
transformation because it
still occurred when
enzymes had destroyed
the RNA.

6. Hershey and Chase
(1952)
 Found viruses that
attack bacteria did so
by injecting their DNA
not proteins.

7. Discovery of DNA Structure
Erwin Chargaff
(1949)
 Found that the DNA
molecule was double-
stranded.
 Adenine = Thymine
 Guanine = Cytosine

8. Rosalind Franklin
 Discovered that the
DNA molecule is a
helix (twisted)
through X-ray
diffraction research.

9. James Watson and
Francis Crick
 Used the research of
the others to figure
out the exact structure
of the DNA molecule.

10. DNA Structure
 Nucleotides –
 DNA is made up of
nucleotides.
 Each nucleotide consists of
deoxyribose sugar, phosphate,
and one of four nitrogen bases.
 Nitrogen Bases –
 The nitrogen bases are,
adenine, thymine, guanine, and
cytosine.
 Base Pairing Rule –
 Nitrogen bases are bonded with
hydrogen bonds according to
the base-pairing rule:
 A – T and G - C

11. DNA Replication
 Helicase
The enzyme helicase causes the
DNA double helix to unwind and unzip
down the middle.
 DNA Polymerase
Loose nucleotides are then bonded
to exposed nitrogen bases on both sides
of the molecule by another enzyme
called DNA polymerase.
 Result
At the end of the process there are
two copies of the original DNA
molecule.
This is called semiconservative
replication because one strand of the
original molecule is contained in each
new molecule.

12. Pneumonia Today
 World Health Organization calls
Pneumonia “ The Forgotten
Killer of Children”
http://whqlibdoc.who.int/publications/2006/9280640489_eng.pdf