DNA: Deoxyribose
Nucleic Acid
The Genetic Material
Chapter 2:
Introduction
to DNA
Ms. Gaynor
Honors
Genetics
DNA
• Deoxyribose nucleic acid
 type of nucleic acid
– What is the other type of
nucleic acid?
• RNA
• DNA function
– to hold genetic code
– Genetic code = genetic
instructions to make proteins
• DNA is found in nucleus of
eukaryotic cells
• Found in nucleoid region in
prokaryotes
The Short History of
DNA and Genetics
(Part 1)
• From 1866-1953
Searching for Genetic Material
• Gregor Mendel
(1866):
– discovered that
inherited traits are
determined by
discrete units, or
'genes,’ - passed on
from the parents.
• Freidrich
Miescher(1868):
– discovered DNA
– Isolated something
new from the nuclei
of eukaryotic cells
• Later called DNA!!!
Searching for Genetic Material
• Thomas Hunt Morgan
(1910):
– Worked with fruit flies
• Specifically eye color of these flies!
– Discovered genes are located (linked) on
chromosomes
Searching for Genetic Material
• Fredrick Griffith
(1928):
– Studied effects of
virulent (virus-causing)
bacteria vs. nonvirulent
bacteria injected into mice
– Used transformation:
• Inserted foreign DNA and
changed protein/ trait
– believed that the
transforming agent was
an inheritance molecule.
Nonvirulent
vs.
Virulent
Bacteria
ROUGH:
harmless
SMOOTH:
kill
NOT
HARMFUL/BENI
BAD/HARMFUL
Griffith's Transformation
Experiment
• Used the Pneumococcus bacteria
– Include2 types:
• a virulent S strain with a Smooth coat
– kills mice
• a non-virulent R Rough strain
– does not kill mice.
• Heat destroys (kills) living cells!!!
• When heated Smooth (harmful) cells (DEAD)
are mixed with living Rough (benign) cells and
injected into mice, the mouse dies.
– WHY?
http://www.quia.com/files/quia/users/hlrbiology/Animations/08_DNA_and_Proteins/Griffith_Mouse_E
Searching for Genetic Material
http://brookings.k12.sd.us/biology/ch12DNARNA/Chapter%2012A.mpg
Searching for Genetic Material
Oswald Avery, Colin MacLeod, &
Maclyn McCarty (1944):
• Reported that “transforming agent” in
Griffith's experiment was DNA.
• Also used the Pneumococcus
bacteria and test tubes (NOT mice)
The Avery, et al.
Experiment
• Used S (harmful) strain
– Opened up the cells
– Isolated
http://wps.aw.com/bc_russell_ig
en_me_1/
• DNA, proteins and other materials SEPERATELY
– Mixed R bacteria with these different materials
– Only those mixed with DNA were transformed
into S bacteria.
TEST
TUBE
S
S DNA
+
R Bacteria
S PROTEINS
+
R Bacteria


OTHER S
CELL PARTS
(sugar/RNA)
+
R Bacteria

Discovering the Structure of
DNA
Edwin Chargaff (1950)
•Discovered a 1:1 ratio of adenine to
thymine and guanine to cytosine in DNA
samples from a variety of organisms.
Chargaff's Rule (Data)
Relative Proportions (%) of Bases in DNA
A
T
G
C
Human
30.9
29.4
19.9
19.8
Chicken
28.8
29.2
20.5
21.5
Grasshopper
29.3
29.3
20.5
20.7
Sea Urchin
32.8
32.1
17.7
17.3
Wheat
27.3
27.1
22.7
22.8
Yeast
31.3
32.9
18.7
17.1
E. coli
24.7
23.6
26.0
25.7
ORGANISM
Discovering the structure of
DNA
Chargaff’s Rules
A=T
C=G
Chargaff movie and Building Blocks movie
http://www.hhmi.org/biointeractive/dna
/animations.html
Discovering the structure of
DNA
Maurice Wilkins
(1952)
• Photographed DNA using xray crystallography
• Worked with another
scientists named Rosalind
Franklin
• Awarded the 1962 Nobel
Prize for Physiology or
Medicine with Watson and
Crick
Linus Pauling’s TRIPLE helix
Linus Pauling
(1954)
• proposed a triple
helix structure for DNA
Pauling Triple Helix Model
http://www.hhmi.org/biointeractive/dna/animations.html
Discovering the structure of
Photo 51
DNA
Rosalind Franklin
(1952)
•Obtained sharp X-ray diffraction
photographs of DNA (Photo 51)
•Watson and Crick used her data 
revealed its helical shape
•Watson and Crick went on to
win Nobel Prize (1962) for their
DNA model
How did PHOTO 51
reveal DNA’s helical
shape?
• X-rays passing through a helix
diffract at angles perpendicular to
helix making an "X" pattern, which
favors an equal diameter "helix".
She finally gets credit 
Rosalind Franklin University of Medicine
and Science, located on Green Bay Road in
North Chicago, Illinois
Searching for Genetic Material
Alfred Hershey & Martha Chase
(1952)
– Confirmed DNA was genetic material
– Used bacteriophages (viruses)
– HYPOTHESIZED DNA, not protein,
is the hereditary material
Searching for Genetic
Material
Hershey and Chase
Experiment Animation
http://highered.mcgrawhill.com/sites/0072437316/student_view0/chapter14/a
nimations.html
Searching for Genetic Material
Hershey and Chase Experiment
Discovering the structure of DNA
James Watson & Francis Crick
(1953)
•Discovered double helix structure
•Solved the three-dimensional structure
of the DNA molecule
Watson Constructing Bair Pairs movie
http://www.hhmi.org/biointeractive/dna/animations.html