Chapter 12 DNA

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Chapter 12DNA RNA

• Section 12-1DNA

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Griffith Transformation

• 1928
• Studying Natural Bacterial Pneumonia caused by
• Streptococcus pneumoniae
• Smooth (pathogenic)
• Rough (non-pathogenic)

S. pneumonia in sputumNotice capsuleGram
Positive Diplococci
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Streptococcus pneumonia
Type 3VERY Mucoid
OptochinDisc
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Griffiths Experiments

• Injected Mice
• Smooth Mice Died
• Rough Mice Didnt Get Sick
• Heat Killed Smooth
• Mice Didnt Get Sick
• Illness Not Caused By Poison

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Transformation

• Mixed Heat Killed Smooth With Rough Live
  Bacteria.
• Mice Died
• Autopsy Revealed Lungs Full Of Smooth Strain of
  Bacteria
• HOW??

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Griffiths Transformation
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Transformation

• Heat Killed Smooth Bacteria
• Still Contained The Information On How To Become
  Smooth
• And Could Transmit That Info
• And Transform Rough Bacteria To The Smooth
  (Pathogenic) Form

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Avery DNA

• 1944
• Repeated Griffiths Work
• But Treated The Extract From Heat Killed Smooth
  Bacteria To Destroy Specific Types Of Compounds

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Avery DNA

• Treated Extract To Destroy
• Proteins
• Lipids
• Carbohydrates
• RNA
• Transformation Still Occurred

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Avery DNA

• Then They Treated Extract Destroyed DNA
• Transformation Did NOT Occur
• DNA Was The Transforming Factor

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Avery DNA

• Key Concept
• Avery and other scientists discovered that DNA
  stores and transmits the genetic information from
  one generation of an organism to the next
  generation.

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Hershey-Chase Experiment

• 1952
• Studied Virus Particles, Especially Bacteriophages

Martha Chase Alfred Hershey
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Hershey-Chase Experiment

• Bacteriophages
• Composed of DNA or RNA
• and a Protein Coat
• Figured Whichever Part Entered The Bacteria
  Carried The Genes
• Used Radioactive Markers

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Radioactive Markers

• Grew Viruses In Cultures Containing
• Radioactive Phosphorus ( 32P )
• and
• Radioactive Sulfur ( 35S )
• Proteins Contain No Phosphorous
• DNA Contains No Sulfur

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Radioactive Markers

• Therefore
• If The Interior Of The Bacteria Contained
• ( 32P ) Then DNA Contained Genes
• ( 35S ) Then Protein Contained Genes

Nearly All The Bacteria Contained ( 32P
) Therefore DNA Contained Genes
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Hershey-Chase
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Hershey - Chase

• Key Concept
• Hershey and Chase concluded that the genetic
  material of the bacteriophage was
• DNA, not Protein.

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The Structure of DNA

• Scientists still didnt know
• How information was carried between generations
• How genes were structured
• How genes were copied

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The Structure of DNA

• DNA is a long Molecule of repeating nucleotides
• Each nucleotide has 3 parts
• 5 Carbon Sugar (Deoxyribose)
• 1 Phosphate Group
• 1 Nitrogenous Base

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The Structure of DNA

• There are 4 Nitrogenous Bases in DNA
• The 4 Bases fit into two groups or types
• Group 1 Purines
• Adenine
• Guanine
• Group 2 Pyrimidines
• Cytosine
• Thymine

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Purines Pyrimidines
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The Structure of DNA

• DNA Backbone
• Sugar Phosphate Groups
• Nitrogenous Bases
• Stick Out Join Sideways

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The Structure of DNA

• Chargaffs Rules
• Discovered That Certain Nucleotides Were Always
  Present In The Same Percentages
• Adenine Thymine
• Guanine Cytosine
• In Each Species Different
• Nobody Knew Why

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The Structure of DNA

• X-Ray Diffraction
• Early 1950s
• Rosalind Franklin
• Doesnt Show Structure But Provides Clues
• DNA Twisted In Coils
• Two Strands
• Nitrogenous Base In Center

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Photo 51
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The Double Helix

• Watson Crick
• Building 3Dimensional Models
• 1953 Saw FranklinsX-ray Work
• Immediately Recognized What The Structure Had To
  Be
• The Double Helix

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Watson Crick

• Key Concept
• Watson Cricks Model of DNA was a Double Helix,
  in which Two (2) Strands were wound around each
  other.

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Double Helix
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Watson Crick

• Discovered The Double Helix
• Held Together By Hydrogen Bonds Between The
  Nitrogenous Bases
• Base Pairing
• AT and GC
• Explained Chargaffs Rule