Ch'9 DNA: The Genetic Material

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Ch.9 DNA The Genetic Material

• Bio P
• Mr. Q

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Section 9.1 Identifying the Genetic Material

• Who helped identify the genetic material?
• Griffiths experiments
• Discovered transformation (the uptake and use of
  DNA by a bacteria)

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Averys experiments

• Is genetic info carried in a protein or nucleic
  acid (DNA)?
• Protein destroying enzyme
• DNA destroying enzyme
• Discovered transformation occurred because of DNA
  not protein.

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Hershey and Chase

• Is it protein or DNA?
• They worked with bacteriophages viruses that
  infect bacteria
• Lets look at their experiment (Fig 9-3)

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What does this mean?

• Conclusion The DNA of the virus was infecting
  the bacteria, NOT the protein coat of the virus.

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Section 9.2

• The Structure of DNA

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Who discovered the structure?

• Francis Crick and James Watson

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What is DNA made of?

• Nucleotides are the base units of DNA.
• It has two strands that twist.
• Double helix

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What are the 3 parts of a nucleotide?

• Phosphate group
• 5-carbon sugar (DNA-deoxyribose)
• Nitrogen containing base 4 bases

• Adenine
• Thymine
• Cytosine
• Guanine

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What are the two groups of bases?

• Adenine (A)
• Guanine (G)
• Thymine (T)
• Cytosine (C)

• Purines
• Pyrimidines

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Who are the scientists that contributed to the
discovery?

• Erwin Chargaff
• that the amount of
• adenine thymine,
• cytosine guanine
• in an organism.

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Wilkins and Franklin

• Using X-rays they were able to see the structure
  of the DNA molecule.

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Watson and Crick

• They built a three-dimensional model of DNA and
  won a Nobel prize.

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What are the base-pairing rules?

• The pairing arrangement of the nitrogen bases
  between the two strands.
• A T
• G C
• A-T have two hydrogen bonds.
• G-C have three hydrogen bonds.

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Section 9.3

• The Replication of DNA

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How is DNA copied?

• Lets remember
• Bases are complementary.
• Complementary - the sequence (order) of bases
  on one strand determines the sequence of bases on
  the other strand.
• This means that they match up to each other.
  Base-pairing rules.

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• One old strand serves as a template (pattern), on
  which the other new strand is built.
• DNA replication the process of making a copy of
  DNA.

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What are the steps of DNA replication?

• Recall that DNA replication occurs in the S phase
  of the cell cycle.
• There are 3 steps (see fig 9-9)
• The two original strands separate.

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• DNA helicases - enzymes used to unwind (split the
  double helix) by breaking the hydrogen bonds b/t
  the bases.
• Proteins attach to prevent the strands from
  reforming.
• Replication fork - area where the DNA separates.

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• DNA polymerases add complementary nucleotides to
  each strand.
• DNA polymerase - enzyme that adds nitrogen bases
  according to the base pairing rules.

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• Two DNA molecules form that are identical to the
  original DNA molecule.

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How are errors checked?

• DNA polymerase also proofreads the new strands.
• The previous nucleotide pair have to be correct
  for it to move on.
• If it is not correct it backtracks and fixes the
  error.
• http//www.ncc.gmu.edu/dna/repanim.htm
• http//www.johnkyrk.com/DNAreplication.html

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Why are replication forks important?

• DNA is copied in about 100 sections, each 100,000
  nucleotides long.
• Why would this be an important feature for a
  eukaryote?
• Since the eukaryotic DNA is so long this allows
  the DNA to be copied at a faster rate.