Searching for Genetic Material

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Searching for Genetic Material

• Oswald Avery, Colin MacLeod, Maclyn McCarty
  (1944)
• Reported that transforming agent in Griffith's
  experiment was DNA.
• Also used the Pneumococcus bacteria and test
  tubes (NOT mice)

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The Avery, et al. Experiment

• Used S (harmful) strain
• Opened up the cells
• Isolated
• DNA, proteins and other materials SEPERATELY
• Mixed R bacteria with these different materials
• Only those mixed with DNA were transformed into S
  bacteria.

http//wps.aw.com/bc_russell_igen_me_1/
OTHER S CELL PARTS (sugar/RNA) R Bacteria ?
S PROTEINS R Bacteria ?
S DNA R Bacteria ?
TEST TUBES
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Discovering the Structure of DNA

• Edwin Chargaff (1950)
• Discovered a 11 ratio of adenine to thymine and
  guanine to cytosine in DNA samples from a variety
  of organisms.

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Chargaff's Rule (Data)
Relative Proportions () of Bases in DNA Relative Proportions () of Bases in DNA Relative Proportions () of Bases in DNA Relative Proportions () of Bases in DNA Relative Proportions () of Bases in DNA
ORGANISM A T G C
Human 30.9 29.4 19.9 19.8
Chicken 28.8 29.2 20.5 21.5
Grasshopper 29.3 29.3 20.5 20.7 
Sea Urchin 32.8 32.1 17.7 17.3
Wheat 27.3 27.1 22.7 22.8
Yeast 31.3 32.9 18.7 17.1
E. coli 24.7 23.6 26.0 25.7
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Discovering the structure of DNA
Chargaffs Rules A T C G
Chargaff movie and Building Blocks
movie http//www.hhmi.org/biointeractive/dna/anima
tions.html
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Discovering the structure of DNA

• Maurice Wilkins (1952)
• Photographed DNA using x-ray crystallography
• Worked with another scientists named Rosalind
  Franklin
• Awarded the 1962 Nobel Prize for Physiology or
  Medicine with Watson and Crick

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Linus Paulings TRIPLE helix

• Linus Pauling
• (1954)
• proposed a triple helix structure for DNA

Pauling Triple Helix Model http//www.hhmi.org/bio
interactive/dna/animations.html
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Discovering the structure of DNA
Photo 51
Rosalind Franklin (1952)

• Obtained sharp X-ray diffraction photographs of
  DNA (Photo 51)
• Watson and Crick used her data ? revealed its
  helical shape
• Watson and Crick went on to win Nobel Prize
  (1962) for their DNA model

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How did PHOTO 51 reveal DNAs helical shape?
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•  X-rays passing through a helix diffract at
  angles perpendicular to helix making an "X"
  pattern, which favors an equal diameter "helix".

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She finally gets credit ?
Rosalind Franklin University of Medicine and
Science, located on Green Bay Road in North
Chicago, Illinois
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Searching for Genetic Material

• Alfred Hershey Martha Chase (1952)
• Confirmed DNA was genetic material
• Used bacteriophages (viruses)
• HYPOTHESIZED? DNA, not protein, is the hereditary
  material

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Searching for Genetic Material
Hershey and Chase Experiment Animation http//high
ered.mcgraw-hill.com/sites/0072437316/student_view
0/chapter14/animations.html
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Searching for Genetic MaterialHershey and Chase
Experiment
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Discovering the structure of DNA

• James Watson Francis Crick (1953)
• Discovered double helix structure
• Solved the three-dimensional structure of the DNA
  molecule

Watson Constructing Bair Pairs movie http//www.hh
mi.org/biointeractive/dna/animations.html