DNA REPLICATION

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DNA REPLICATION

• Chapter 11, Section 1

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Think, Pair, Share

• 1.What is the building block of DNA?
• Nucleotides (Sugar, Phosphate, Base)
• 2. What is the shape of DNA?
• Double Helix
• 3. What 2 bonds hold nucleotides together?
• Hydrogen bonds(bases) Covalent (Sugar Phosphate)
• 4. During what part of the Cell Cycle does DNA
  replicate?
• Interphase (S-phase)
• 5. What pairs with G? A? Number of Hydrogen
  Bonds?
• Guanine Cytosine (3), Adenine Thymine (2)
• 6. Which are the Purines? Pyrimidines? Rungs for
  each?
• Purines AG (2 rungs) Pyrimidines TC (1 rung)
• 7. What are the complimentary bases for the
  following sequence? AATCCGC
• TTAGGCG

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How DNA Replicates

• DNA has to be replicated before a cell divides
• New cells at the end of Mitosis need identical
  strands of DNA

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Think, Pair, Share

• 8. Explain semiconservative replication
• One strand of DNA gets used as a template
  (pattern) to make a new strand that matches up
  with it
• Special enzymes are required for DNA replication

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Steps of DNA Replication

• 1. Replication begins with the unwinding
  separation of the DNA double helix by enzymes
  called helicases
• The process is like unzipping a zipper

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• 2. New strands are formed by enzymes called DNA
  polymerase which adds complimentary nucleotides
  to the original strands
• 3. Leading Strand (continuous) vs. Lagging
  Strand (discontinuous)

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Semi-conservativeReplication

• Each new strand compliments one of the original
  strands
• 2 identical DNA double helix strands are the
  result of DNA replication

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• http//www.wiley.com/college/pratt/0471393878/stud
  ent/animations/dna_replication/index.html

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Uneven formation of DNA

• When DNA is replicating one strand forms
  continuously and the other strand forms in chunks
  with spaces that need to be filled in

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DNA 5 to 3

• Anti-parallel
• In the double helix one strand is right-side
  up, the other strand is up-side down
• If not, the nitrogen bases wouldnt be able to
  bond together

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• 5 and 3 come from how the carbons in the
  5-carbon sugar get numbered

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5 end
3 end
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• DNA polymerase can only add nucleotides to the 3
  end of a strand of DNA
• That means that the newly forming strand is
  forming from 5 to 3
• That means
• One strand gets to form continuously
• The other strand gets formed in chunks called
  Okazaki fragments that need to be connected by
  the enzyme DNA Ligase

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• http//highered.mcgraw-hill.com/olcweb/cgi/pluginp
  op.cgi?itswf535535/sites/dl/free/0072437316
  /120076/micro04.swfDNA20Replication20Fork
• Important Terms- semiconservative replication,
  anti-parallel, 5 to 3
• 3 enzymes you must know the function of are
  Helicase, DNA Polymerase, and Ligase