Chapter 12_ DNA and RNA

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					 Chapter 12:
DNA and RNA
• Genes are made of DNA, a large, complex molecule. DNA
  is composed of individual units called nucleotides. Three of
  these units form a code. The order, or sequence, of a code
  and the type of code determine the meaning of the
  message.

1. On a sheet of paper, write the word cats. List the letters or
   units that make up the word cats.
2. Try rearranging the units to form other words. Remember
   that each new word can have only three units. Write each
   word on your paper, and then add a definition for each word.
3. Did any of the codes you formed have the same meaning?
4. How do you think changing the order of the nucleotides in
   the DNA codon changes the codon’s message?
       12-1 DNA

Once it was known that
traits were inherited the
   next question was:
        HOW?
What molecule holds the
  genetic information?
Discovering the function and
     structure of DNA
          Frederick Griffith, 1928

           Oswald Avery, 1944

  Alfred Hershey and Martha Chase, 1952

              Erwin Chargaff

        Rosalind Franklin, 1950’s

  James Watson and Francis Crick, 1953
     Griffith’s Experiment
• Rough Pneumococcus are harmless. They
  lack a gel capsule that would protect them
  from a host organism's immune system
  attack.
• Smooth Pneumococcus are pathogenic
  (they cause disease), and when injected,
  give a mouse fatal pneumonia.
• Griffiths injected several combinations of
  rough and smooth into hapless mice, and
  found...
    Results of Experiment
– live rough --> mice okay
– live smooth --> mice pushing up daisies
– killed (boiled) rough --> mice okay
– killed (boiled) smooth --> mice okay
– live smooth + killed rough --> mice kick the
  bucket
– live rough + killed smooth --> MICE
  CROAK! This was a surprise!
              The Puzzle
• When Griffiths autopsied the mice, he
  found LIVE SMOOTH PNEUMOCOCCUS!!
• The heat killed bacteria had passed their
  disease-causing ability to the harmless
  rough bacteria.
• He called this transformation:
   harmless, live rough bacteria
  TRANSFORMED into deadly smooth
  bacteria. But how?!
            Conclusions
• The factor passed from the heat-killed
  smooth bacteria to the live rough
  bacteria must contain information to
  transform harmless bacteria into
  deadly bacteria.
• Perhaps this transforming factor was
  a gene!
      Avery’s Experiment
• Oswald Avery (1944)
 –Repeated Griffith’s experiment in an
  attempt to find molecule
  responsible for transformation
 –Was it a Protein? Lipid?
  Carbohydrate? Nucleic acid?
       Heat-killed smooth bacteria mixture

Treated with enzymes to
 destroy carbs, lipids,      Treated with enzymes to
   protein and RNA               Destroy DNA




   Mouse Dies                    Mouse lives!



             CONCLUSION:
DNA STORES AND TRANSMITS GENETIC INFO.
      The Hershey and Chase
           Experiment
• Used more advanced science to see if
  Avery was right about DNA
• Worked with bacteriophages (Viruses
  that attack bacteria)
• Side by side experiments were
  performed to see if it was the protein or
  the DNA of the virus that infected the
  host
• Conclusion: AVERY WAS RIGHT!
The DNA was passed into the host, not the protein coat.
    The components and
     structure of DNA
Once Scientists agreed that it was definitely
  DNA that contained and passed on the
   genetic information the next question
                   was...
              What is DNA?
          What does it look like?
           What is it made of?
            How does it work?
• DNA is composed of small units
  called nucleotides
• There are four different kinds:
  Adenine, Guanine, Cytosine
  and Thymine
• Chargaff realized that in DNA
  the # of Adenine was always
  similar to the number of
  Thymine. The # of Cytosine
  was always similar to the
  number of Guanine...
           Chargaff’s Rule
• A always
  bonds to T

• C always
  bonds to G
          Rosalind Franklin
• Franklin and Maurice Wilkins
  at King's College, (London,
  England) performed X-ray
  diffraction studies
• Franklin noticed a diffraction
  pattern in DNA that showed
  that DNA was 2-stranded and
  a helix-shape
           Watson and Crick
• Used Franklin’s X-ray
  image to build a
  model of the DNA
  structure
• The Double helix
  shape of DNA
  explained how it could
  carry information and
  how that information
  could be copied

				
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