Deoxyribonucleic Acid (DNA)

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Deoxyribonucleic Acid(DNA)

• Students will be successful when they can..
• When they can summarize the experiments leading
  to the discovery of DNA as the genetic material
• Diagram and label the basic structure of DNA
• Describe the basic structure of the eukaryotic
  chromosome

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Discovering DNAThe Fredrick Griffith Experiment
(1928)
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• Griffith used two different strains of a bacteria
  that causes Pneumonia (Streptococcus pneumoniae)
• One strain had a sugar coat (the S strain), and
  caused pneumonia killing a mouse by injection.
• the other did not have a coat and is referred to
  as the rough strain (R strain). It did not kill
  the mouse by injection.

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• Griffith discovered that if he heated the S
  strain it would die, and no longer kill the
  mouse.
• But, if he mixed the heated S strained with some
  live R strain (non disease-causing) the R strain
  would be transformed into the S strain, killing
  the mouse.
• The Smooth strain was extracted from the dead
  mouse and cultured. It was still the rough
  strain, but had developed characteristics of the
  disease causing strain.

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Griffiths Conclusions

• Griffith concluded that there had been a
  transformation from the live R bacteria to Live S
  bacteria.
• This experiment set the stage for the search to
  identify the transforming substance.

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Oswald Averys Experiment (1944)

• Avery and Colleagues identified the molecule that
  transformed the R strain of bacteria into the S
  strain.
• He isoladed different macromolecules, such as
  DNA, Protien, and lipids.
• When the live R strain was exposed to the DNA of
  the S strains DNA, it was transformed into the
  disease causing S strain.

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Hershey and Chase Experiment (1952)

• Alfred Hershey and Martha Chase published results
  of experiments that provided definitive evidence
  that DNA is the transforming factor

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The Experiment

• Hershey and Chase used a new technique called
  radioactive labeling using radio-active
  Phosphorus(P32) and Radioactive sulfur (S35).
• Proteins take up sulfur not phosphorus, so the
  proteins are labeled.
• DNA takes up Phosphorus, but not sulfur,
  therefore labeling the DNA.

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Viruses and Bacteria are Grown in Medium
Containing 32P, and another group of Viruses are
grown in a medium of 35S. And then Blended up
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The Blender dislodges the viruses from the
bacteria cells, and the bacteria is seperated
from the liquid containing the viruses.
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Results of the Hershey Chase Experiment

• Results bacterial cells infected with the
  radioactive label of 32P had incorporated 32P
  into its cells.
• The bacteria infected with the 35S did not
  incorporate it into itself, the 35S was left in
  the broth.

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Conclusions

• DNA not Protein was the genetic material that
  could be passed from generation to generation in
  viruses.

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II. DNA Structure

• After Hershey and Chase found that DNA was the
  molecule responsible for inheritance a scientific
  race had begun to discover the structure of the
  DNA molecule.

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What is a Nucleotide

• The structure of Nucleotides includes A
  phosphate sugar backbone, with one of the 5
  nitrogenous bases (ATCG,U).

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The 4 Nucleotide bases of DNA and Uracil (RNA)

• Uracil (only found in bacterial RNA)

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Weve seen this structure before!!(this is a
molecular homology, and evidence for evolution)
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The Brilliance of Erwin Chargaff (1950)

• Chargraff analyzed the numbers of each nucleotide
  (GCTA) in the entire genomes of different
  species. Heres what he found!

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DUDE!!! The number Of Adenine and Thymine Are
the Same!!!!
Dude!!! The number of Cytosine and Guanine Match
Too!!!!
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DUDE!!!! So, What!!!

• Well, for starters it implies that the Adenine
  and Thymine are related some how, as well as
  Cytosine and Guanine?
• Like, maybe theyre totally complementary base
  pairs. DUDE!!!

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Rosalind Franklin

• Rosalind Franklin took a new job at Kings
  college in London working with a technique called
  X-ray Diffraction.
• X-ray diffraction shoots X-rays at molecules and
  measure how the energy waves are broken up.
  Allowing photographs of molecules to be taken.

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Photograph 51

• Photograph 51 showed a pattern describing a
  double helix.
• This photograph along with other data was taken
  without her knowledge by her Mentor and shared
  with two other scienctists.

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James Watson and Francis Crick

• Both were working at Cambridge University
  (London) when they saw Rosalind photograph.
• They soon realized that structure of the DNA was
  a double helix, and built their famous model.

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The DNA Model that won themthe Nobel Prize

1. Two outside strands consist of alternating
   deoxyribose and phosphates.
2. Cytosine and guanine bases pair to each other by
   three hydrogen bonds
3. Thymine and adenine bases pair to each other by
   two hydrogen bonds

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Orientation of the Two Strands

• The top strand of DNA is the 5 (5 prime) strand
  and at the end of the top rail is the 3 (3
  prime) and said to be 5 to 3 orientated.
• The bottom rail is the opposite, 3 to 5.
• This is referred to as antiparallel.

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The Announcement

• In 1953 Watson and Crick surprised the scientific
  community by publishing a one-page paper in the
  journal Nature suggesting a structure for the DNA
  molecule as well as a hypothesized a method of
  replication.