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Transcript of Chapter 13 Powerpoint l
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DNA Structure
& Function
Chapter 13
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DNA Structure& Function 2
Outline
Genetic Material
Transformation
DNA Structure
Watson and Crick
DNA Replication
Prokaryotic versus Eukaryotic
Replication Errors
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DNA Structure& Function 3
Genetic Material
Frederick Griffith investigated virulence ofStreptococcus pneumoniae
Concluded that virulence passed from the
dead strain to the living strainTransformation
Further research by Avery et al
Discovered that DNA is the transformingsubstance
DNA from dead cell was being incorporated
into genome of living cells
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4Griffiths Transformation Experiment
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DNA Structure& Function 5
Reproduction of Viruses
Viruses consist of a protein coat (capsid)surrounding a nucleic acid core
Bacteriophages are viruses that infectbacteria
Hershey and Chase:
Radioactively labeled the DNA core andprotein capsid of a phage
Results indicated that DNA, not the protein,enters the host
The DNA of the phage contains genetic
information for producing new phages
B i d B i h
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6Bacteria and Bacteriophages
H h d Ch E i
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7Hershey and Chase Experiments
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DNA Structure& Function 8
Structure of DNA
DNA contains:
Two Nucleotides with purine bases
-Adenine (A)
-Guanine (G)
Two Nucleotides with pyrimidine bases-Thymine (T)
-Cytosine (C)
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DNA Structure& Function 9
Chargaffs Rules
The amounts of A, T, G, and C in DNA:Identical in identical twinsVaries between individuals of a speciesVaries more from species to species
In each species, there are equal amounts of:A & TG & C
All this suggests DNA uses complementary
base pairing to store genetic infoHuman chromosome estimated to contain, onaverage, 140 million base pairs
Number of possible nucleotide sequences4,140,000,000
N l tid C iti f DNA
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10Nucleotide Composition of DNA
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DNA Structure& Function 11
Watson and Crick Model
Watson and Crick, 1953
Constructed a model of DNA
Double-helix model is similar to a twistedladder
-Sugar-phosphate backbones make up the sides
-Hydrogen-bonded bases make up the rungs
Received a Nobel Prize in 1962
X R Diff ti f DNA
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12X-Ray Diffraction of DNA
W t /C i k M d l f DNA
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13Watson/Crick Model of DNA
S
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DNA Structure& Function 14Replication:
Prokaryotic vs. Eukaryotic
Prokaryotic Replication
Bacteria have a single circular loop
Replication moves around the circular DNAmolecule in both directions
Produces two identical circles
Cell divides between circles, as fast as every20 minutes
DNA S
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DNA Structure& Function 15Replication:
Prokaryotic vs. Eukaryotic
Eukaryotic ReplicationDNA replication begins at numerous points alonglinear chromosome
DNA Unwinds and unzips into two strands
Each old strand of DNA serves as a template for anew strand
Complementary base-pairing forms new strand oneach old strand
Replication bubbles spread bi-directionally until theymeet
Semiconservative:
One original strand is conserved in each daughter
molecule
Semiconservative Replication
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16Semiconservative Replicationof DNA
Meselson and Stahls
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17Meselson and StahlsDNA replication experiment
Replication:
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18Replication:Prokaryotic vs. Eukaryotic
DNA St t 19
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DNA Structure& Function 19
Replication Errors
Genetic variations are the raw material forevolutionary change
Mutation:
A permanent (but unplanned) change in base-pair sequence
-Some due to errors in DNA replication
-Others are due to to DNA damage
DNA repair enzymes are usually available to
reverse most errors
DNA Structure 20
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DNA Structure& Function 20
Review
Genetic Material
Transformation
DNA Structure
Watson and Crick
DNA Replication
Prokaryotic versus Eukaryotic
Replication Errors
Ending Slide Chapter 13
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DNA Structure
& Function
Ending Slide Chapter 13