Ch. 9 Notes DNA: The Genetic Material

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Ch. 9 NotesDNA The Genetic Material

• By Brianna Shields
• December 8, 2005

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DO NOW

• 1. Which scientist(s) discovered
  transformation?
• 2. Hershey and Chase verified the finding that
  what material is transferred during
  transformation?
• 3. What type of lab organism did Hershey and
  Chase use in their experiments?

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List the terms in your vocab notebook, leaving
about 3-4 spaces between each term

• Vaccine
• Virulent
• Transformation
• Bacteriophage
• Double Helix
• Nucleotide
• Deoxyribose

• Base-pairing Rules
• Complementary Base Pair
• DNA Replication
• DNA Helicase
• Replication Fork
• DNA Polymerase

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GOALS

• Relate Griffiths conclusions to the observations
  he made during the transformation experiments
• Summarize the steps involved in Averys
  transformation experimentsand state the results
• Evaluate the results of the Hershey and Chase
  experiment
• Describe the three components of a nucleotide
• Develop a model of the structure of a DNA
  molecule
• Evaluate the contributions of Chargaff, Franklin
  and Wilkins in helping Watson and Crick determine
  the double helical structure of DNA
• Relate the role of the base pairing rules to the
  structure of DNA
• Summarize the process of DNA replication
• Describe how errors are connected during DNA
  replication
• Compare the number of replication forks in
  prokaryotic and eukaryotic DNA

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DNA The Genetic Material

• Trying to develop a vaccine (killed/weakened
  bacteria or virus introduced to body to protect
  from future infection)

• Griffiths Experiment

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DNA The Genetic Material

• Two strains of streptococcus pneumoniae
• S - virulent (disease causing), has capsule,
  grows in smooth colonies
• R- non disease causing, no capsule, grows in
  rough colonies

• Griffiths Experiment

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DNA The Genetic Material

• 1. Mice injected with S died
• 2. Mice injected with R were healthy

• Griffiths Experiment

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DNA The Genetic Material

• 3. Was bacterial capsule causing death in mice?

• Griffiths Experiment

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DNA The Genetic Material

• 4. Inject mice with dead S bacteria- mice
  remained healthy

• Griffiths Experiment

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DNA The Genetic Material

• 5. Injected mice with heat killed S bacteria-
  (cant reproduce but still have capsule)- mice
  lived

• Griffiths Experiment

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DNA The Genetic Material

• 6. Injected mixed harmless live R with heat
  killed S into mice- mice died

• Griffiths Experiment

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DNA The Genetic Material

• 7. Mouse blood contained R bacteria that had
  acquired capsules (somehow changed and became
  virulent S bacteria)
• Discovered TRANSFORMATION

• Griffiths Experiment

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Griffith's Experiment
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DNA The Genetic Material

• Change in genotype caused when cells take in
  foreign genetic material

• Transformation

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DNA The Genetic Material

• What substance is responsible for transformation?
• Added protein destroying enzymes to heat killed S
  and healthy R mixture- transformation occurred
• Added DNA destroying enzymes to same mixture-
  transformation stopped

• Averys Experiment

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DNA The Genetic Material

• Wanted to confirm that DNA (not proteins) carried
  genetic material

• Hershey and Chase Experiment

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DNA The Genetic Material

• Known facts
• A. Viruses made of DNA or RNA surrounded by
  protective protein coat

• Hershey and Chase Experiment

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DNA The Genetic Material

• Known facts
• B. Bacteriophages (viruses) infecxt bacteria to
  produce more viruses (released when bacteria host
  ruptures)

• Hershey and Chase Experiment

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DNA The Genetic Material

• Known facts
• C. Only DNA in phage contained phosphorus
• D. Only protein coat in phage contained sulfur

• Hershey and Chase Experiment

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DNA The Genetic Material

• 1. Grew a sample of T2 bacteriophage in
  radioactive sulfur medium (would be used in T2s
  protein coat)

• Hershey and Chase Experiment

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DNA The Genetic Material

• 2. Grew a sample of T2 bacteriophage in
  radioactive phosphorus medium (would be used in
  T2s DNA)

• Hershey and Chase Experiment

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DNA The Genetic Material

• 3. Allowed S and P labeled phages to infect E.
  coli bacteria
• Can detect radioactive S and P to see if DNA,
  protein or both are transferred to E. coli

• Hershey and Chase Experiment

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DNA The Genetic Material

• 4. S and P phages removed from bacteria using
  blender
• 5. Centifuge spins heavy bacteria to bottom and
  light phages to liquidy top of mixture

• Hershey and Chase Experiment

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DNA The Genetic Material

• 6. Findings
• A. S label found only in phages (protein never
  injected into E. coli)
• B. P label found mostly in bacteria (DNA
  transferred to E. coli)
• C. New generation of phages from bursted
  bacteria also contained radioactive DNA

• Hershey and Chase Experiment

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DNA The Genetic Material

• 7. Conclusion
• DNA is transferred from virus to bacteria
• Protein remains outside cell
• DNA must be hereditary material (atleast in
  viruses)

• Hershey and Chase Experiment

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Assessment One

• Summarize Griffiths transformation experiments
• Describe how Averys experiment supplied evidence
  that DNA, not protein is the genetic material
• Describe the contributions of Hershey and Chase
  to the understanding that DNA is the genetic
  material
• Why did heat kill Griffiths S bacteria?
• What might Hershey and Chase have concluded if
  they had found P and S in the bacteria cells?

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DNA The Genetic Material

• Established the structure of DNA
• Made a tin and wire model of DNA

• Watson and Crick

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DNA The Genetic Material

• 1. Double helix- 2 strands of linked nucleotides
  twisted around like a winding staircase

• Structure of DNA

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DNA The Genetic Material

• 2. Nucleotides- subunits that make up DNA,
  composed of
• Phosphate group
• Five carbon sugar molecule (deoxyribose)
• Nitrogen containing base (four kinds)
• Adenine
• Guanine
• Thymine
• Cytosine
• Bases pair up to create ladder rungs

• Structure of DNA

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DNA The Genetic Material

• 3. Base classification
• Purines- double ring of C and N atoms
• Adenine and Guanine
• Pyrimidines- single ring of C and N atoms
• Thymine and Cytosine

• Structure of DNA

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DNA The Genetic Material

• 4. Helix held together by weak hydrogen bonds
  between paired bases

• Structure of DNA

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DNA The Genetic Material

• Discovered base pairing rule
• Amounts of adenine and thymine in DNA are always
  the same
• Amounts of cytosine and guanine in DNA are always
  the same
• Amounts of A and T, and G and C differ

• Chargaff

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DNA The Genetic Material

• Bounced X rays off DNA to create pattern
  scattered onto film
• Photos indicate DNA is a tightly coiled helix
  with 2 chains of nucleotides

• Wilkins and Franklins Photographs

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DNA The Genetic Material

• Because of size and structure of bases, only
  certain ones pair up to hold DNA together
• Adenine - Thymine
• Guanine - Cytosine

• Pairing between bases

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DNA The Genetic Material

• Results in complementary base pairs
• Sequence on one strand of DNA can determine
  sequence of other strand

• Pairing between bases

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Assessment Two

• Describe the three parts of a DNA molecule
• Relate the base pairing rules to the structure of
  the DNA
• Describe the two pieces of information from other
  scientists that enabled Watsons and Crick to
  discover the double helical structure of DNA
• Explain why the two strands of the double helix
  are described as complementary
• What would be the complementary strand to DNA
  with the following base sequence AGCTTAGTCA

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DNA The Genetic Material

• Making a copy of DNA
• Complementary strands of DNA serve as template
  for replicating DNA
• Occurs during S phase of cell cycle (before
  division)

• Replication of DNA

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DNA The Genetic Material

• Steps
• A. DNA helicase unwinds and opens DNA by
  breaking H bonds between bases

• Replication of DNA

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DNA The Genetic Material

• Steps
• B. Helix separates at replication forks (Y
  shape), proteins attach to DNA and hold helix open

• Replication of DNA

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DNA The Genetic Material

• Steps
• C. DNA polymerase enters fork, moves along DNA
  strand adding nucleotides to exposed bases
  according to pairing rule
• Proofreads, removes and fixes any mismatched
  nucleotides
• Reduces error to 1 in a billion

• Replication of DNA

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DNA The Genetic Material

• Steps
• D. DNA polymerase continues until DNA is copied,
  then it is signaled to detach

• Replication of DNA

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DNA The Genetic Material

• Result 2 new DNA double helices created
  (identical to each other and original DNA)

• Replication of DNA

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DNA The Genetic Material

• In circular prokaryotic DNA
• 2 replication forks that move away from one
  another until they meet on other side of DNA
  circle

• Rate of DNA replication

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DNA The Genetic Material

• In eukaryotic DNA
• End o end replication would take a month for one
  strand of DNA
• Have multiple replication forks so several DNA
  portions are replicated simultaneously
• One human chromosome takes 8 hours

• Rate of DNA replication

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Assessment Three

• Explain the two roles that enzymes play in DNA
  replication
• Explain the relationship between DNA polymerases
  and mutation
• State the effect of multiple replication forks on
  the speed of replication in eukaryotes
• If a mutation occurs during the formation of an
  egg cell or sperm cell, is that mutation more
  significant or less significant than a mutation
  that occurs in a body cell?

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Websites

• Gene Scene
• DNA Workshop
• The Geee! In Genome
• Putting DNA to work
• Kids Genetics DNA
• Hershey and Chase Experiment Animation
• DNA Replication Animation
• Another DNA Replication Animation