DNA: Deoxyribose
Nucleic Acid
The Genetic Material
Introduction
to DNA
(PART 1)
Ms. Kim
Honors
Biology
What does DNA stand for?
• Deoxyribonucleic acid
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
information/instructions for making
proteins
• DNA is found in nucleus of
eukaryotic cells
• Found in nucleoid region in
prokaryotes
What is DNA made of?
• DNA is a macromolecule
– Made up of nucleotides
– Covalently and hydrogen bonded together
• Double stranded
– Helix
– “Spiral”
What is a nucleotide?
• Molecule made of
– Deoxyribose sugar
– A phosphate group
– A nitrogenous base
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.
• Thomas Hunt
Morgan (1910):
– 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.
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 the harmfulness of S strain
• When heated S is mixed with live R and
injected into mice, the mouse dies.
• WHY?
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)
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.
•Noticed that:
# of Adenine = # of Thymine
# of Cytosine = # of Guanine
•“Chargaff’s Rule”
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
C and G are held more tightly together
because they are connected by three
hydrogen bonds, whereas A and T are held
by only two.
Chargaff movie and Building Blocks movie
http://www.hhmi.org/biointeractive/dna
/animations.html
Discovering the structure
of DNA
Maurice Wilkins (1952)
• Studied DNA using x-ray
crystallography with another
scientist named Rosalind Franklin
• He showed Franklin’s x-ray
photograph without Franklin’s
consent to Watson and Crick,
which helped them discover
DNA’s structure.
• Awarded the 1962 Nobel Prize for
Physiology or Medicine with
Watson and Crick
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
• 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
How was the structure of DNA
discovered?
• 1953 – Watson and Crick
– Wilkins shows Watson and Crick the x-ray
pictures from Franklin
• This information gave Watson & Crick the evidence
to conclude DNA has a helical shape
– Made model of DNA which was made up of
two chains of nucleotides
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
DNA Structure (PART 2)
From 1953
What is the Double Helix?
•Shape of DNA
•Looks like a twisted
ladder
•2 coils are twisted
around each other
•Double means 2
•Helix means coil
DNA - basics
• Deoxyribonucleic Acid
• Stores and transmits
info
• Tells the cells which
make and
• Made up of nucleotides
– Phosphate group
– Sugar
– Nitrogen bases
• Double helix structure
genetic
proteins to
when to make them
The Structure of DNA
• Made out of nucleotides
•Includes a phosphate group,
nitrogenous base and 5-carbon
pentose sugar
Nucleotide
Structure
1
“link”
in a
DNA
chain
A Polynucleotide
Nucleotide
Structure
• MANY
nucleotides
(“links”)
bonded
together
DNA has a
overall
negative
charge b/c
of the PO4-3
(phosphate
group)
The Structure of DNA
Backbone = alternating P’s and sugar
•Held together by COVALENT bonds
(strong)
•Inside of DNA molecule = nitrogen
base pairs
•Held together by HYDROGEN
bonds (weaker)
Backbone
• Phosphodiester
Bond
–The covalent that
holds together the
backbone
–Found between P
& deoxyribose
sugar
–STRONG!!!
Minor
Groove
Major
Groove
DNA is antiparallel
• Antiparallel means that the 1st
strand runs in a 5’ 3’
direction and the 2nd 3’ 5’
direction
– THEY RUN IN
OPPOSITE or
ANTIPARALLEL
DIRECTIONS
• P end is 5’ end (think: “fa” sound)
• -OH on deoxyribose sugar is 3’
end
– 5’ and 3’ refers to the carbon # on
the pentose sugar that P or OH is
attached to
Nitrogen Bases (2 types)
• Purines
(small word, big base)
– Adenine
– Guanine
• Pyrimidines
– (big word, small base)
– Cytosine
– Thymine
• Chargaff’s rules
– A=T, C=G
– Hydrogen Bonds attractions between
the stacked pairs; WEAK bonds
Why Does a Purine Always
Bind with A Pyrimidine?
DNA Double Helix
• http://www.sumanasinc.com/webc
ontent/animations/content/DNA_st
ructure.html
• Watson & Crick said that…
– strands are complementary; nucleotides line up
on template according to base pair rules
(Chargaff’s rules)
• A to T and C to G
• LET’S PRACTICE…
• Template strand:
•
3’AATCGCTATAC5’
Complementary strand:
5’TTAGCGATATG3’