1. 1 What Is
    the Evidence that the Gene Is DNA?

    In 1920s,  WHO      , working with
    two strains of Streptococcus pneumoniae determined that a transforming
    principle from dead cells of one strain produced a heritable change in the
    other strain.
          Frederick Griffith
  2. What Is the
    Evidence that the Gene Is DNA?

    To identify the transforming principle:
    WHO    treated samples to destroy
    different molecules;

    •        If DNA was
    destroyed, the transforming activity was lost.

    •       There was no loss of activity with destruction of
    proteins, carbohydrates, or lipids.
  3. •          
    In 1952, WHO
    confirmed DNA is the genetic material

    T2 bacteriophage (virus that attacks
    bacteria) consists of DNA core packed in protein coat 
    Hershey and Chase
  4. •       Used bacteriophage T2 virus to determine whether DNA, or
    protein, is the genetic material

    •       Bacteriophage proteins were labeled with 35S;
    the DNA was labeled with 32P
    • Hershey-Chase
    • experiment
  5. Experiment
    (Part 2)


    13.1 What Is
    the Evidence that the Gene Is DNA?

    Genetic transformation of eukaryotic cells, transfection,
    can be demonstrated.

    •       A genetic marker—a gene that confers an observable
    phenotype—is used.

    Any cell can be transfected, even an egg
    cell—result is a transgenic organism
  6. 1950s What Is
    the Structure of DNA?

    •       The structure of DNA was determined using many lines of

    One crucial piece came from X-ray
    crystallography from chemists
    Wilkins and Franklin
  7. What Is the
    Structure of DNA?

    Chemical composition also provided clues:

    DNA is a polymer of nucleotides: Deoxyribose,
    a phosphate group, and a nitrogen-containing base.
    Wilkins and Franklin
  8. What
    Is the Structure of DNA?
          Purines: adenine (A), guanine (G)

           Pyrimidines: cytosine (C), thymine (T)
  9. 2 What Is
    the Structure of DNA?

    Model building started by Linus
    Pauling—building 3-D models of possible molecular structures.

    WHO used model
    building and combined all the knowledge of DNA to determine its structure.
  10. Watson and Crick
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