dna structure & replication. ch. 10.1 griffith’s transformation experiment 1928 – frederick...
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DNA Structure & DNA Structure & ReplicationReplication
Ch. 10.1Ch. 10.1GriffithGriffith’’s Transformation s Transformation
ExperimentExperiment1928 – Frederick Griffith is studying how
certain strains of bacteria cause pneumonia and inadvertently makes a discovery about how genetic information is passed from organism to organism
His Experiment:Grow two slightly different strains (types) of
bacteriaOne strain proven harmless and other
deadlyLaboratory mice are injected with these
strains
GriffithGriffith’’s Resultss Results
What caused GriffithWhat caused Griffith’’s s results?results?
• The heat-killed strain passed on its disease-causing ability to the live harmless strain.
• In Griffith’s words, one strain of bacteria was TRANSFORMED into another.
• Was the “Transforming” Factor: Protein or DNA?
Avery, MacLeod, McCarty
Isolate macromolecules present in S-strain (virulent) bacteria to see which is capable of transforming R-strain (non-virulent) bacteria.
Only DNA can transform!
The Hershey-Chase The Hershey-Chase ExperimentExperiment
• Alfred Hershey & Martha Chase studied viruses, which are non-living particles smaller than a cell that can infect living organisms.
• Bacteriophages: specific group of viruses that infect bacteria.
• OBJECTIVE: To determine which part of the virus (protein or DNA) enters a bacteria it is infecting.
What did Hershey & What did Hershey & Chase do?Chase do?
• If Hershey and Chase could determine which part of the virus entered an infected cell, they would learn whether genes were made of protein or DNA.
• To accomplish this, they grew viruses in cultures containing radioactive isotopes of phosphorus-32 (32P) and sulfur-35 (35S).
• Some viruses had P-32 in their DNA, and others had S-25 in their protein coat.
• If S-35 is found in the bacteria, it would mean that viruses release their protein and if P-32 is found in the bacteria it would mean that viruses release their DNA.
Recall: Method of Bacteriophage Recall: Method of Bacteriophage InfectionInfection
o When a bacteriophage enters a bacterium, the virus attaches to the surface of the cell and injects its genetic information into it.
o The viral genes replicate to produce many new bacteriophages, which eventually destroy the bacterium.
o When the cell splits open, from viral overload, hundreds of new viruses burst out and can infect surrounding cells
Hershey-Chase ResultsHershey-Chase Results
So… The genetic material in bacteriophages was the DNA,DNA, (not the protein)!!!
Ch. 10.2-10.3: DNA Ch. 10.2-10.3: DNA StructureStructure
• Made of monomers called nucleotidesnucleotides
• Nucleotide structure:
A nucleotide can have one A nucleotide can have one of four bases:of four bases:
Types of bases: Adenine Guanine Cytosine Thymine
A & G are bigger and are called purinesC & T are smaller and are called pyrimidines
ChargaffChargaff’’s Rule & s Rule & Rosalind FranklinRosalind Franklin
Chargaff (A=T; C=G)Discovered that in almost any DNA sample, the % G% G nearly equals the % C% C and the % A% A nearly equals the % T % T
Franklin: X-ray picture helps figure out structureused x-ray diffraction to get information about the structure of DNA. •She aimed an X-ray beam at concentrated DNA samples and recorded the scattering pattern of the X-rays on film.
Watson & CrickWatson & Crick• Using clues from Franklin’s X-ray pattern, shown
to them by Maurice Wilkins, James Watson and Francis Crick built a 3-D model that explained how DNA carried information and could be copied.
• Watson, Crick & Wilkins were awarded the 1962 Nobel Prize in Physiology or Medicine for their work.
Base-PairingBase-Pairing• Watson & Crick discovered that bonds can only form
between certain base pairs, Adenine & Thymine and Cytosine & Guanine.
• The base-pairing rule means that purinespurines only pair with pyrimidinespyrimidines, making the rungs equally spaced like a ladder.
• The nitrogenous bases are held together by hydrogen bonds. – A & T are held together by TWO hydrogen bonds– C & G are held together by THREE hydrogen bonds
DNA is a DNA is a ““double-helixdouble-helix”” or or twisted ladder:twisted ladder:
oThe “backbone” or sides of the DNA molecule are made up of alternating sugars and phosphates and the “rungs” are made up of interlocking nitrogen bases.
oThe sugars and the phosphates are held together by covalent bonds and the nitrogen bases are held together by hydrogen bonds.
Molecular Structure of DNA
DNA Structure
Chromosomes & DNAPROKARYOTES:• In prokaryotic cells (bacteria), DNA is
located in the cytoplasm.• Most prokaryotic cells have a single DNA
molecule that holds all of the genetic information
EUKARYOTES:• 1000x the DNA as prokaryotes• DNA is held in chromosomes located in
the nucleus• Chromosome # varies widely from one
species to the next
DO NOW:
• What category of macromolecules does DNA fit into?
• What is the monomer of a DNA molecule?
• What are the three parts of this molecule?
• How do the nucleotides fit together in a molecule of DNA?
• How is the 3D structure of DNA described?
33 end end 55 end end
33 end end55 end end
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22
44
1133
55
22
4411
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DNA Replication Tutorials
• http://www.hhmi.org/biointeractive/dna/DNAi_replication_vo2.html Excellent narrated animation; pause, highlight, take notes; use Styrofoam model
• Good additional animation of lagging strand http://sites.fas.harvard.edu/~biotext/animations/replication1.html
DNA Replication• Before a cell can divide, it’s DNA must be replicated or
copied in the S-phase of the cell cycle. • In most prokaryotes, replication begins at a single point
and continues in two directions.• In eukaryotes, replication occurs in hundreds of places
simultaneously and proceeds until complete.
• Sites of replication are called replication forks.
– DNA replication begins at the origins of replication– DNA unwinds at the origin to produce a “bubble”– Replication proceeds in both directions from the origin– Replication ends when products from the bubbles merge
with each other
– DNA replication occurs in the 5’ 3’ direction– Replication is continuous on the 3’ 5’ template– Replication is discontinuous on the 5’ 3’ template,
forming short segments
10.5 DNA replication proceeds in two directions at many sites simultaneously
Copyright © 2009 Pearson Education, Inc.Copyright © 2009 Pearson Education, Inc.
Animation: Animation: Leading StrandLeading Strand
10.5 DNA replication proceeds in two directions at many sites simultaneously
– Proteins involved in DNA replication– DNA helicase unwinds the double helix– DNA polymerase adds nucleotides to a growing chain– DNA ligase joins small fragments into a continuous chain
Copyright © 2009 Pearson Education, Inc.Copyright © 2009 Pearson Education, Inc.
Animation: Animation: Lagging StrandLagging Strand
Animation: Animation: DNA Replication ReviewDNA Replication Review
Animation: Animation: Origins of ReplicationOrigins of Replication
Origin of replicationOrigin of replication Parental strandParental strand
Daughter strandDaughter strand
BubbleBubble
Two daughter DNA moleculesTwo daughter DNA molecules
Parental DNAParental DNA
3355
DNA polymeraseDNA polymerasemoleculemolecule
DNA ligaseDNA ligase
3355
Overall direction of replicationOverall direction of replication
Daughter strandDaughter strandsynthesizedsynthesizedcontinuouslycontinuously
3355
3355
Daughter Daughter strandstrandsynthesizedsynthesizedin piecesin pieces
Visual Summary of DNA replication
AnimationAnimation
Replication Bubbles
ParentalParentalmoleculemoleculeof DNAof DNA
NucleotidesNucleotides
Both parentalBoth parentalstrands servestrands serveas templatesas templates
Two identicalTwo identicaldaughterdaughter
molecules of DNAmolecules of DNA Each Each ““newnew”” strand of DNA consists of one strand of DNA consists of one original original
templatetemplate strand and one strand and one newly madenewly made strand. strand. This allows for This allows for proofreadingproofreading, using the template , using the template
strand as the strand as the ““mastermaster””..
DNA REPLICATION is semi-conservative
Chromosome Structure• Eukaryotic chromosomes contain DNA and
protein tightly packed together to from chromatin.
• Chromatin consists of DNA tightly coiled around proteins called histones.
• DNA & histone molecules form nucleosomes, which pack together to form thick fibers of chromosomes.
Do Now:
• Why would DNA need to be photocopied? What is the name of this process? Where does it occur?
• Replication is described as semi-conservative. Explain.
• Distinguish between the leading and
lagging strand during DNA replication.
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