DNA replication and repair (Ch. 14.3 and 14.5)

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DNA replication and repair (Ch. 14.3 and 14.5)
2011-04-20 02:58:08

Exam 3
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  1. Before cell division, all DNA in the nucleus should replicate during what phase?
  2. Semi-conservative process
    DNA double helix opens up, and each strand is copied onto a new DNA strand, using old strands as templates. Newly formed helices have one old and one new strand.
  3. DNA polymerase
    • -DNA synthesis is catalyzed by this enzyme.
    • -Adds nucleotides to the 3' end of the growing DNA strand.
    • -DNA synthesis always from 5' to 3' direction.
    • -Polymerase doesn't add nucleotides until there's an open 3' end with hydroxyl group (-OH)
  4. How does replication get started?
    • -Double helix splits apart in some place.
    • -Appear as bubbles
  5. Helicase
    • -Moves along the opening unzipping the double helix, expanding the replication bubble in both directions.
    • -Single strand DNA binding proteins bind to the open region of the helix to keep the strands joining again.
  6. Primase
    • -Enzyme that adds a short RNA fragment that serves as a primer with an open 3' OH group.
    • -DNA polymerase starts adding nucleotides to make the new strand.
  7. Leading strand
    Strand that is synthesized in the direction of helix opening
  8. Lagging Strand
    • Strand synthesized in the direction away from the helix opening.
    • -Synthesized in fragments, known as Okazaki fragments.
    • -When second fragment runs into first, RNA primer is destroyed and space filled with DNA.
    • -DNA ligase joins the two fragments.
  9. How do mistakes get corrected?
    • -DNA polymerase has the ability to proofread its own work.
    • -If wrong nucleotide is added by mistake, it backs up, removes the wrong nucleotide, and adds the correct one.
    • -If mistakes left behind by DNA polymerase, there's other proof reading enzymes to correct them.
  10. What can cause damages to DNA?
    • -Chemicals
    • -poisons
    • -harmful rays
    • -and natural aging process
  11. Excision repair
    • When damage is recognized, it cuts off the damaged area, and makes a new DNA strand to fill the gap.
    • DNA ligase joins the new piece of DNA with old.