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NUCLEIC ACIDS ARE UNIQUE IN
THEIR ABILITY TO DIRECT THEIROWN REPLICATION FROM
MONOMERS.
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READ THE
BEGINNING
OFCONCEPT
16.1 IN
CAMPBELL,
P. 305.
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GROUP PROJECT:
GRIFFITH AVERY, ET. AL.
HERSHEY AND CHASE
ERWIN CHARGAFF
ROSALIND FRANKLIN
MAURICE WILKINS
JAMES WATSON AND FRANCIS CRICK
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The Search for the Genetic Material
Poster Project
Questions to Answer for the
Presentation:
1.What were the scientists actuallylooking for in their research?
2.What did they do in their
experiment?
3.How did it impact understanding of
DNA?
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Figure 16-01
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LE 16-2
Living S cells
(control)
Living R cells
(control)
Heat-killed
S cells (control)
Mixture of heat-killed
S cells and living
R cells
Mouse dies
Living S cells
are found in
blood sample
Mouse healthy Mouse healthy Mouse dies
RESULTS
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LE 16-3
Bacterialcell
Phage
head
Tail
Tail fiber
DNA
100nm
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LE 16-4
Bacterial cell
Phage
DNA
Radioactive
protein
Emptyprotein shell
PhageDNA
Radioactivity
(phage protein)
in liquid
Batch 1:
Sulfur (35S)
RadioactiveDNA
Centrifuge
Pellet (bacterialcells and contents)
PelletRadioactivity
(phage DNA)
in pellet
Centrifuge
Batch 2:Phosphorus (32P)
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Portrait of Erwin Chargaff. 1930
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LE 16-6
Franklins X-ray diffraction
photograph of DNA
Rosalind Franklin
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LE 16-7c
Space-filling model
LE 16 7
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LE 16-7
5 end
3 end
5
end
3 end
Space-filling modelPartial chemical structure
Hydrogen bond
Key features of DNA structure
0.34 nm
3.4 nm
1 nm
THESE MEASUREMENTS
ARE IMPORTANT AND DO
NOT VARY!
NOTICE THE NUMBER OF HYDROGEN
BONDS BETWEEN THE BASE PAIRS
ABOVE?
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LE 16-5Sugarphosphate
backbone
5
end
Nitrogenousbases
Thymine (T)
Adenine (A)
Cytosine (C)
DNA nucleotidePhosphate
3 endGuanine (G)
Sugar (deoxyribose)
1. HOW ARE THE
NUCLEOTIDES THE
SAME?
2. WHAT ARE THETHREE PARTS OF A
NUCLEOTIDE?
3. HOW ARE THE
NUCLEOTIDES
DIFFERENT?4. HOW DOES THE 5
END DIFFER FROM
THE 3 END?
5. WHICH ONES ARE
PURINES? WHICHONES ARE
PYRIMIDINES?
LE 16 7b
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LE 16-7b
5 end
3 end
5 end
3 end
Partial chemical structure
Hydrogen bond
EXPLAIN WHAT
IS MEANT BY
THE TWO SIDES
OF THE DOUBLE
HELIX BEINGANTIPARALLEL.
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For a great review of DNA structure and
replication go to Biocoach athttp://www.phschool.com/science/biology_place/biocoach/dnarep/intro.html
http://www.phschool.com/science/biology_place/biocoach/dnarep/intro.htmlhttp://www.phschool.com/science/biology_place/biocoach/dnarep/intro.html8/10/2019 Chapter 16 2013
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LE 16 9 1
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LE 16-9_1
The parent molecule hastwo complementarystrands of DNA. Each baseis paired by hydrogenbonding with its specificpartner, A with T and G withC.
LE 16-9 4
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LE 16-9_4
The parent molecule hastwo complementarystrands of DNA. Each baseis paired by hydrogenbonding with its specificpartner, A with T and Gwith C.
The first step in replicationis separation of the twoDNA strands.
Each parental strand nowserves as a template thatdetermines the order ofnucleotides along a new,complementary strand.
The nucleotides areconnected to form thesugar-phosphate back-bones of the new strands.Each daughter DNAmolecule consists of oneparental strand and onenew strand.
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WHAT WERE THE THREE
HYPOTHESES/MODELS
CONSIDERED FOR THE
PROCESS OF DNA
REPLICATION?
LE 16-10
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LE 16 10
Conservative
model. The two
parental strands
reassociate after
acting as
templates for
new strands,thus restoring
the parental
double helix.
Semiconservative
model. The two
strands of the
parentalmolecule
separate, and
each functions as
a template for
synthesis of a
new, comple-
mentary strand.
Dispersive model.
Each strand ofboth daughter
molecules
contains
a mixture of
old and newly
synthesized
DNA.
Parent cellFirstreplication
Secondreplication
LE 16-10LE 16-11
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LE 16 10
Conservative
model. The two
parental strands
reassociate after
acting as
templates for
new strands,thus restoring
the parental
double helix.
Semiconservative
model. The two
strands of the
parentalmolecule
separate, and
each functions as
a template for
synthesis of a
new, comple-
mentary strand.
Dispersive model.
Each strand ofboth daughter
molecules
contains
a mixture of
old and newly
synthesized
DNA.
Parent cellFirstreplication
Secondreplication
LE 16 11
Bacteria
cultured in
medium
containing15N
DNA sample
centrifuged
after 20 min
(after first
replication)
DNA sample
centrifuged
after 40 min
(after second
replication)
Bacteria
transferred to
medium
containing14N
Less
dense
More
dense
Conservative
model
First replication
Semiconservative
model
Second replication
Dispersive
model
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LE 16-11a
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LE 16 11a
Bacteria
cultured inmedium
containing15N
DNA sample
centrifuged
after 20 min(after first
replication)
DNA sample
centrifuged
after 40 min(after second
replication)
Bacteria
transferred tomedium
containing14N
Less
dense
More
dense
LE 16-11b
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Conservative
model
First replication
Semiconservative
model
Second replication
Dispersive
model
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For more details of Meselson and
Stahls experiment seehttp://www.sumanasinc.com/webcontent/anisamples/majorsbiology/meselson.h
tml
http://www.sumanasinc.com/webcontent/anisamples/majorsbiology/meselson.htmlhttp://www.sumanasinc.com/webcontent/anisamples/majorsbiology/meselson.htmlhttp://www.sumanasinc.com/webcontent/anisamples/majorsbiology/meselson.htmlhttp://www.sumanasinc.com/webcontent/anisamples/majorsbiology/meselson.html8/10/2019 Chapter 16 2013
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THE STEPS OF
REPLICATION IN E.
COLI
MOST OF THE PROCESS IS FUNDAMENTALLY
SIMILAR IN PROKARYOTES AND IN
EUKARYOTES.
LE 16-12
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In eukaryotes, DNA replication begins at many sitesalong the giant DNA molecule of each chromosome.
Two daughter DNA molecules
Parental (template) strand
Daughter (new) strand0.25 m
Replication fork
Origin of replication
Bubble
In this micrograph, three replicationbubbles are visible along the DNAof a cultured Chinese hamster cell(TEM).
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The replisomeis a complex
molecular machine that carries
out replication of DNA. It is
made up of a number of
subcomponents that each
provide a specific function
during the process of replication.
LE 16-13
http://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/DNA8/10/2019 Chapter 16 2013
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New strand
5
end
PhosphateBase
Sugar
Template strand
3
end 5 end 3
end
5
end
3
end
5
end
3
end
Nucleoside
triphosphate
DNA polymerase
Pyrophosphate
WHAT PROVIDES THE ENERGY TO ADD NEW NUCLEOTIDES?
LE 16-14
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Parental DNA
5
3
Leading strand
3
5
3
5
Okazaki
fragmentsLagging strand
DNA pol III
Template
strand
Leading strand
Lagging strand
DNA ligaseTemplate
strand
Overall direction of replication
WHATS THE
DIFFERENCEBETWEEN A
LEADING AND
A LAGGING
STRAND?
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leading strand
The new continuous complementary DNA strand synthesized along the template strand
in the mandatory 5 ( 3 direction.
lagging strand
A discontinuously synthesized DNA strand that elongates in a direction away from thereplication fork.
Okazaki fragment
A short segment of DNA synthesized on a template strand during DNA replication. ManyOkazaki fragments make up the lagging strand of newly synthesized DNA.
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HOW DOES THE SYNTHESIS
OF THE
LAGGING STRAND WORK?
LE 16-15_1
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53
Primase joins RNA
nucleotides into a primer.
Templatestrand
5 3
Overall direction of replication
LE 16-15_2P i j i RNA
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53
Primase joins RNA
nucleotides into a primer.
Template
strand
5 3
Overall direction of replication
RNA primer3
5
35
DNA pol III addsDNA nucleotides tothe primer, formingan Okazaki fragment.
LE 16-15_3P i j i RNA
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53
Primase joins RNA
nucleotides into a primer.
Template
strand
5 3
Overall direction of replication
RNA primer3
5
35
DNA pol III addsDNA nucleotides tothe primer, formingan Okazaki fragment.
Okazaki
fragment3
5
5
3
After reaching thenext RNA primer (not
shown), DNA pol IIIfalls off.
LE 16-15_4Primase joins RNA
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53
Primase joins RNA
nucleotides into a primer.
Template
strand
5 3
Overall direction of replication
RNA primer3
5
35
DNA pol III addsDNA nucleotides tothe primer, formingan Okazaki fragment.
Okazaki
fragment3
5
5
3
After reaching thenext RNA primer (not
shown), DNA pol IIIfalls off.
33
5
5
After the second fragment isprimed, DNA pol III adds DNAnucleotides until it reaches the
first primer and falls off.
LE 16-15_5Primase joins RNA
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53
Primase joins RNA
nucleotides into a primer.
Template
strand
5 3
Overall direction of replication
RNA primer3
5
35
DNA pol III addsDNA nucleotides tothe primer, formingan Okazaki fragment.
Okazaki
fragment3
5
5
3
After reaching thenext RNA primer (not
shown), DNA pol IIIfalls off.
33
5
5
After the second fragment isprimed, DNA pol III adds DNAnucleotides until it reaches thefirst primer and falls off.
33
5
5
DNA pol I replacesthe RNA with DNA,adding to the 3 endof fragment 2.
LE 16-15_6Primase joins RNA
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53
Primase joins RNA
nucleotides into a primer.
Template
strand
5 3
Overall direction of replication
RNA primer3
5
35
DNA pol III addsDNA nucleotides tothe primer, formingan Okazaki fragment.
Okazaki
fragment3
5
5
3
After reaching thenext RNA primer (not
shown), DNA pol IIIfalls off.
33
5
5
After the second fragment isprimed, DNA pol III adds DNAnucleotides until it reaches thefirst primer and falls off.
33
5
5
DNA pol I replacesthe RNA with DNA,adding to the 3 endof fragment 2.
3
3
5
5
DNA ligase forms abond between the newestDNA and the adjacent DNAof fragment 1.
The laggingstrand in the regionis now complete.
LE 16-16
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5
3
Parental DNA
3
5
Overall direction of replication
DNA pol III
Replication fork
Leadingstrand
DNA ligase
Primase
OVERVIEW
PrimerDNA pol III
DNA pol I
Lagging
strand
Lagging
strand
Leading
strand
Leading
strand
Lagging
strandOrigin of replication
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For a review of DNA replication and
interactive quiz questions go tohttp://www.wiley.com/college/pratt/0471393878/instructor/animations/dna_replication/index.html
http://www.wiley.com/college/pratt/0471393878/instructor/animations/dna_replication/index.htmlhttp://www.wiley.com/college/pratt/0471393878/instructor/animations/dna_replication/index.htmlhttp://www.wiley.com/college/pratt/0471393878/instructor/animations/dna_replication/index.htmlhttp://www.wiley.com/college/pratt/0471393878/instructor/animations/dna_replication/index.html8/10/2019 Chapter 16 2013
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http://www.nature.com/nrc/journal/v1/n1/animation/nrc1001-022a_swf_MEDIA1.html
CHECK THIS OUT
http://www.nature.com/nrc/journal/v1/n1/animation/nrc1001-022a_swf_MEDIA1.htmlhttp://www.nature.com/nrc/journal/v1/n1/animation/nrc1001-022a_swf_MEDIA1.htmlhttp://www.nature.com/nrc/journal/v1/n1/animation/nrc1001-022a_swf_MEDIA1.htmlhttp://www.nature.com/nrc/journal/v1/n1/animation/nrc1001-022a_swf_MEDIA1.html8/10/2019 Chapter 16 2013
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PROOFREADING AND
REPAIRING DNA
LE 16-17
A thymine dimer
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DNA
ligase
DNA
polymerase
DNA ligase seals the
free end of the new DNA
to the old DNA, making the
strand complete.
Repair synthesis by
a DNA polymerase
fills in the missing
nucleotides.
A nuclease enzyme cuts
the damaged DNA strandat two points and the
damaged section is
removed.
Nuclease
A thymine dimer
distorts the DNA molecule.
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LE 16-18
5
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End of parental
DNA strands
5
3
Lagging strand 5
3
Last fragment
RNA primer
Leading strand
Lagging strand
Previous fragment
Primer removed but
cannot be replaced
with DNA because
no 3
end availablefor DNA polymerase
5
3
Removal of primers and
replacement with DNA
where a 3
end is available
Second round
of replication
5
3
5
3
Further rounds
of replication
New leading strandNew leading strand
Shorter and shorter
daughter molecules
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telomerase
An enzyme that catalyzes the lengthening of
telomeres in germ cells. The enzyme includes a
molecule of RNA that serves as a template for
new telomere segments.
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THE CANCER CONNECTION
1. NORMAL SHORTENING OF
TELOMERES MAY PROTECT FROM
CANCER; LIMITS NUMBER OF TIMES
A SOMATIC CELL CAN DIVIDE
2. TELOMERASE ACTIVITY FOUNDIN SOME CANCEROUS SOMATIC
CELLS; ALLOWS CANCER CELLS TO
PERSIST?
3. TELOMERASE A TARGET FOR
CANCER DIAGNOSIS AND
CHEMOTHERAPY?
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histone
A small protein with a high proportion of positively chargedamino acids that binds to the negatively charged DNA and
plays a key role in its chromatin structure.
nucleosome
The basic, bead-like unit of DNA packaging in eukaryotes,
consisting of a segment of DNA wound around a protein corecomposed of two copies of each of four types of histone.
LE 19-2a
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DNA double helix
Histone
tails
His-
tones
Linker DNA
(string)
Nucleosome
(bead)
10 nm
2 nm
Histone H1
Nucleosomes (10-nm fiber)
A FIFTH TYPE; NEEDED FOR
FURTHER PACKING
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LE 19-2c
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300 nm
Loops
Scaffold
Protein scaffold
Looped domains (300-nm fiber)
LE 19-2d
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Metaphase chromosome
700 nm
1,400 nm
SO WE CAN SEE HOW DNA IS PACKED UP FOR MITOSIS OR
MEIOSIS, BUT WHEN ELSE MIGHT IT BE USEFUL TO PACK OR
UNPACK DNA?
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SEE ACTIVITY ON DNA
PACKING ON THE
CAMPBELL WEBSITE
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chromatin
The complex of DNA and proteins that makes up a eukaryotic
chromosome. When the cell is not dividing, chromatin exists
as a mass of very long, thin fibers that are not visible with alight microscope.
heterochromatin
Nontranscribed eukaryotic chromatin that is so highlycompacted that it is visible with a light microscope during
interphase.
euchromatinThe more open, unraveled form of eukaryotic chromatin that
is available for transcription.
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