Introduction to DNA

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Introduction to DNA its History

• How have we come to know that DNA codes for
  characteristics of all living things??

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Deoxyribonucleic acid (DNA)

• Made of Nucleotides
• (which are stacked together)
• A nucleotide has 3 Parts
• Deoxyribose Sugar
• Phosphate
• N-Base

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The Beginning

• 1928
• British Scientist Frederick Griffith studies
  bacteria looking for the cause of pneumonia
• Found two specific strains or cultures of
  bacteria that looked different when growing on
  petri dishes
• -one grew in smooth-edged groups (caused
  disease)
• -other one produced colonies that were
  rough and ragged around the edges (harmless)

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FRED GRIFFITHTransformation of bacteria
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FRED GRIFFITHTransformation of bacteria
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FRED GRIFFITHTransformation of bacteria
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FRED GRIFFITHTransformation of bacteria
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FRED GRIFFITHTransformation of bacteria
CONCLUSION Something transforms the bacteria
making them take on characteristics that are not
expected. That something is DNA.
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Results of Griffiths Experiment

• Discovery of the process of transformation
• Somehow the heat-killed bacteria had passed their
  disease-causing ability to the harmless strain
• The harmless strain had been transformed into a
  disease-causing strain
• Hypothesized that some factor was responsible
  for this change

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Next Discovery

• 1944
• -American, Oswald Avery, continued bacteria
  research of Griffith
• -Knew were 4 types of organic compounds that
  make up all life
• - used enzymes to destroy lipids,
  carbohydrates, proteins, and RNA in an extract
  from the disease causing bacteria.

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What Did Avery Find??

• Transformation still occurred, so obviously the
  molecules they had destroyed were not responsible
  for transformation.
• Only organic molecule left that had not been
  destroyed was DNA
• When repeated experiment with DNA-destroying
  enzymes, no transformation occurred.DNA was the
  key to heredity!

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Moving Forward

• 1952
• -Americans Alfred Hershey and Martha Chase
• -worked with viruses called bacteriophages
• -viruses are simple DNA or RNA core and a
  protein coat around them
• -when infect, bacteriophages inject DNA or RNA
  into cell and protein coat is left outside
• -used radioactive markers to trace
• phosphorus-32 (32P) for DNA
• sulfur-35 (35S) for protein coat

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Figure 16.2a The Hershey-Chase experiment phages
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Hershey-Chase Experiment
Bacteriophage with phosphorus-32 in DNA
Phage infectsbacterium
Radioactivity inside bacterium
Phage infectsbacterium
Bacteriophage with sulfur-35 in protein coat
No radioactivity inside bacterium
Go to Section
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So What Were the Results?

• When viruses were separated from the bacteria and
  tested for radioactivity, all of the
  radioactivity from the bacteria was found to be
  32P
• Conclusion genetic material of the
  bacteriophage that was transferred was DNA

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Race for the structure of DNA

• 1940
• -Erwin Chargaff discovers that percentages of A
  and T are equal in any sample of DNA same is
  true for C and G
• 1944
• - Linus Pauling discovers that proteins can
  have a helical shape
• 1952
• - Rosalind Franklin takes pictures of DNA
  molecule using technique called X-ray
  diffraction, shows that DNA has helical shape

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Figure 16.4 Rosalind Franklin and her X-ray
diffraction photo of DNA
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More Advances

• 1951-1952
• -Maurice Wilkins works with X-ray diffraction
  and sees same pattern as Franklin, shares info
  with James Watson
• April 1953
• -James Watson and Francis Crick build first
  model of DNA (are awarded Nobel Prize in 1960s)

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Figure 5.x3 James Watson and Francis Crick
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DNA Structure Revealed !!

• Exists as a double helix
• Uprights made up of alternating deoxyribose
  (sugar) and phosphate groups
• Nitrogenous bases are attached to the sugars
• Bases in DNA are adenine, thymine, cytosine, and
  guanine
• A pairs with T, C pairs with G and vice-versa
• A and G are purines larger, double rings
• T and C are pyrimidines smaller, single rings

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Deoxyribonucleic acid (DNA)

• Made of Nucleotides
• (which are stacked together)
• A nucleotide has 3 Parts
• Deoxyribose Sugar
• Phosphate
• N-Base

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Figure 16.6 Base pairing in DNA
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Why does A always pair with T (or U), and G with
C?
Distance between uprights is 2 nm (nanometers)
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Chromosome Structure of Eukaryotes
Section 12-2
Nucleosome
Chromosome
DNA double helix
Coils
Supercoils
Hitones
Go to Section
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DNAs JOBS

• DNA makes copies of itself (DNA replication)
• DNA encodes information (protein synthesis)
• 3. DNA controls cells and tells them what to do
  (gene expression)
• 4. DNA changes by mutation

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How Does DNA Make Copies of Itself?

• DNA Replication- a process through which DNA in
  the chromosomes is copied.
• Each strand of DNA serves as a pattern to make a
  new DNA molecule.
• Replication produces two molecules from one
• Each new molecule has one original strand and one
  new strand.

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So How Does This Work.

• Replication begins as an enzyme, helicase, breaks
  the hydrogen bonds between nitrogen bases that
  hold the strands together (unzipping the DNA).
• Free floating nucleotides bind to the single
  strands by base pairing
• An enzyme, DNA polymerase, binds these new
  nucleotides into the strand.
• DNA polymerase proofreads the new strands of
  DNA
• Repeat until entire DNA molecule has been
  unzipped and replicated
• Close up with enzyme ligase.

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Final Results of Replication

• Each new strand of DNA is a complement of one of
  the original strands.
• Result There are two copies of the organisms
  genetic information
• Genetic makeup of organism can be passed on to
  new cells through cell division (mitosis or
  meiosis).

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DNA replication the basic concept
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DNA replication the basic concept
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DNA replication the basic concept
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DNA replication the basic concept
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DNA replication the basic concept
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