Download DNA History and Structure

DNA: Deoxyribose
Nucleic Acid
The Genetic Material
Lecture #22A
Ms. Day
Honors
Biology
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
• Freidrich
Miescher(1868):
– discovered DNA
– Isolated something
new from the nuclei
of eukaryotic cells
• Later called DNA!!!
Searching for Genetic Material
• Fredrick Griffith
(1928):
– Studied effects of
virulent (virus-causing)
bacteria vs. nonvirulent
bacteria injected into mice
• He 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
• 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!!!
• He heated smooth (harmful) cells
– So cells were DEAD!
– Then he mixed them with living Rough (benign)
cells and injected into mice, BUT the mouse dies.
– WHY?
http://www.quia.com/files/quia/users/hlrbiology/Animations/08_DNA_and_Proteins/Griffith_Mouse_E
Searching for Genetic Material
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)
So…DNA is the
transforming
agent!!
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
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
• X-rays passing through a helix
diffract at angles perpendicular to
helix making an "X" pattern, which
favors an equal diameter "helix".
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
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 IS 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
DNA’s Structure
Lecture #22B
Ms. Gaynor
Honors
Biology
DNA and Its
Structure (Part 2)
• From 1953
Recall…
•DNA and RNA are nucleic acids
•An important macromolecule in
organisms that stores and carries genetic
information
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
The Structure of DNA
• Made out of nucleotides
•MONOMERS of nucleic acids
•Includes:
•phosphate group (PO4-3)
• nitrogenous base and
•5-carbon pentose sugar
1 “link” or
monomer
in a DNA
chain
2 Polynucleotides
• 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 PO4-3 & 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
PO4-3 &
deoxyribose sugar
of 2 DIFFERENT
nucleotides
–STRONG!!!
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
DNA in Cells
• 2 broad categories of cells
1. Eukaryotic cells: have nucleus
with DNA
– DNA is contained in structure
called a chromosome
– Chromosomes are a LINEAR
(line) shape with ENDS called
telomeres (protective
“caps”)
2. Prokaryotic cells: no nucleus
(nucleoid region instead) which
contains DNA
– DNA is a CIRCULAR shaped
chromosome without ENDS
(no telomeres)
DNA Bonding
• 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…
AATCGCTATAC3’
Complementary strand: 3’ TTAGCGATATG5’
Template:
5’