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DNA Replication

DNA Replication. May , 2013. DNA Replication. Genetic information needs to be replicated before cell division (mitosis) Mitotic cell division is important for tissue growth, embryonic development and tissue regeneration. 3 Proposed Models. Meselson and Stahl. Semiconservative.

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DNA Replication

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  1. DNA Replication May, 2013

  2. DNA Replication • Genetic information needs to be replicated before cell division (mitosis) • Mitotic cell division is important for tissue growth, embryonic development and tissue regeneration

  3. 3 Proposed Models

  4. Meselson and Stahl

  5. Semiconservative • DNA replication is semiconservative • Each DNA molecule is composed of a parent strand and a newly synthesized strand

  6. Mechanism of DNA Replication 1) SEPARATE 2) REPLICATE 3) REPAIR

  7. 1) Separate • DNA strands need to be unraveled and kept separate • DNA helicase – enzyme that unwinds the double-helix by disrupting H-bonds • Single-stranded binding proteins – bind to the single-stranded DNA to prevent annealing • DNA gyrase – relieves tension from the unwinding of DNA; cuts both strands and reseals the strands

  8. DNA gyrase Topoisomerase (swivels) DNA helicase Single-stranded binding proteins (SSB)

  9. Replication Bubbles • In eukaryotes, there are multiple sites of replication forming “bubbles” in the DNA • 1 replication site = 700 days to replicate • Multiple sites = 5-10 hours

  10. 2) Replicate • Primase – creates an RNA primer (10-60 base pairs) in front of the DNA template strand • The primer acts as a start sequence to direct replication; easy to remove • DNA polymerase III (DNAP3) – recognizes the primer and synthesizes DNA in the 5’ to 3’ direction by adding deoxyadenosine triphosphates

  11. Adding Bases • Free bases are found in the nucleoplasm • DNAP3 uses the energy from breaking the phosphates of the deoxyadenosine triphosphates to drive the process • The two phosphates are recycled

  12. Leading vs Lagging Strand • DNA is synthesized in the 5’ to 3’ direction • Leading strand – synthesized continuously • Lagging strand – synthesized in short fragments • Primers are added continuously • DNAP3 makes complementary segments called “Okazaki fragments” • DNA polymerase I (DNAP1) – removes primers • DNA ligase – joins the Okazaki fragments

  13. Lagging Strand

  14. 3) Repair • DNAP3 and DNAP1 proofread the newly synthesized strand • Both can function as an exonuclease (cuts out nucleotides) • They backtrack past the mistaken nucleotide, excises it and continues adding nucleotides to the complementary strand • First checkpoint

  15. Summary • http://highered.mcgraw-hill.com/sites/dl/free/0072437316/120076/bio23.swf • http://www.youtube.com/watch?v=-mtLXpgjHL0&feature=related

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