Frederick Griffith (1928)

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Frederick Griffith (1928)
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Frederick Griffith (1928)
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Frederick Griffith (1928)
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Frederick Griffith (1928)
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Avery, McCarty MacLeod (1944)

• Only DNA (not protein, lipid or carbohydrates)
  TRANSFORM bacteria

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Hershey Chase (1952)

• Bacteria eaters- Phage virus particles
• (image from the 1990s)

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Hershey Chase (1952)

• Viruses are made of protein and nucleic acid
  ONLY
• Something in the virus enters the cell and
  gets incorporated into the genetic material
  (whatever that might be) of the bacteria
• That something transforms bacteria to turn
  them into virus production factories
• Protein is full of a lot of the atom Sulfur
  nucleic acids have very little
• DNA is full of the atom phosphorus proteins
  have very little

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Hershey Chase (1952)
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Hershey Chase (1952)

• Bacteria eaters- Phage virus particles
• (image from the 1990s)

DNA
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Generally accepted

• Nucleic acids are made of four components
• Phosphate group
• Sugar (deoxyribose ribose)
• Nitrogenous bases
• Pyrimidines (1-ring)
• Purines (2-ring)

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Erwin Chargaff (1947)

• All living cells have DNA (plus many that are
  not living)
• Between species there is wide variation in the
  overall percentages of A, T, G C
• However, in all species A T, C G
• E.g.- Human A- 30.3, T 30.3 , G 19.5, C
  19.9
• Chargaffs Rules
• Also, a cell before meiosis has twice as much
  DNA as a cell (sperm, egg) after

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Franklin (1951- 52)

• X-ray diffraction crystallography

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Franklin (1951- 52)

• Image 51
• Helix
• Repeating units
• unit cell of specific
• parameters
• Phosphates on
• the outside (bases
• inside) backbone
• C2 form
• Parallel width along length

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Watson Crick (1952)

• Parallel width along length
• Backbone must be parallel
• Bases fill in the space between the rungs
• But how?

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Watson Crick (1952)

• Many Ah-Hahs
• A bonds to T (2 bonds), C bonds to G (3 bonds)
  and NOT vice versa
• Consistent with whose previous research?

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Watson Crick (1952)
Nucleotide

• Many Ah-Hahs
• C2 form?
• All the data fit
• with Franklins,
• Chargaffs, etc
• conclusions

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Watson Crick (1952)

• All the data fit with Franklins, Chargaffs,
  etc conclusions
• And it looks good too!

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Watson Crick (1952)

• Part I- the model (what it looks like)
• Part II- how it works (the secret of life)
• Complimentarity replication
• The Central Dogma information storage

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Watson Crick (1952)

• The Central Dogma information storage

DNA
PROTEIN
RNA
Enzymes
Cell Structure
Nucleic Acids
Lipids
Carbohydrates
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Watson Crick (1952)

• Complimentarity replication
• Their Model (paper 2)
• Semi-conservative replication