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DNA Replication and Repair

DNA Replication and Repair. Before a cell can reproduce, it’s DNA must first replicate (make a copy of itself). 1 double helix (parent) replicates to make 2 identical double helices (daughters) Semiconservative Replication. Replication Forks and Bubbles. Leading Strand and Lagging Strand.

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DNA Replication and Repair

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  1. DNA Replication and Repair

  2. Before a cell can reproduce, it’s DNA must first replicate (make a copy of itself).

  3. 1 double helix (parent) replicates to make 2 identical double helices (daughters) Semiconservative Replication

  4. Replication Forks and Bubbles

  5. Leading Strand and Lagging Strand

  6. DNA replication goes in the 5' to 3' direction because DNA polymerase acts on the 3'-OH of the existing strand for adding free nucleotides. So, the leading strand is quickly replicated from end to end. The lagging strand is replicated in chunks. 

  7. An enzyme called DNA gyrase makes a nick in the double helix and each side separates • An enzyme called helicaseunzips the double-stranded DNA by breaking the hydrogen bonds between bases

  8. Several small proteins called single strand binding proteins (SSB) temporarily bind to each side and keep them separated • An RNA primer of 10-60 bases is annealed to a region of single stranded DNA to act as a starting point for replication (primase is the enzyme that builds the primer)

  9. An enzyme complex called DNA polymerase moves down the DNA strands and adds new nucleotides to each strand. • DNA polymerase III synthesizes complementary strands while DNA polymerase I removes primers and replaces them with nucleotides

  10. Polymerase proofreads the bases • An enzyme called DNA ligase seals up the fragments into one long continuous strand • The new copies automatically wind up again

  11. Crash Course Bio: DNA Structure and Replication https://www.youtube.com/watch?v=8kK2zwjRV0M

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