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16B

16B. DNA Replication and Repair. Semiconservative Model. Separate DNA Strands, each side serves as a template for a new strand New nucleotides join according to _____ and ______. Nucleotides are connected-new DNA formed (one old strand and one new strand). Meselson Stahl Test.

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16B

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  1. 16B DNA Replication and Repair

  2. Semiconservative Model • Separate DNA Strands, each side serves as a template for a new strand • New nucleotides join according to _____ and ______. • Nucleotides are connected-new DNA formed (one old strand and one new strand)

  3. Meselson Stahl Test • If conservative: parent in tact • If dispersive: all 4 strands should have old and new • If semiconservative, half old strand and new strand and half new strand • Semiconservative proved true • Funny story • http://www.youtube.com/watch?v=MX5FrexyQyo

  4. Origins of replication • 1 in prokaryotes, many in eukaryotes, form bubbles • _____________: enzyme that opens DNA strand • _____________: point of replication “unzipping”

  5. DNA Polymerase Adds New Nucleotides • Nucleotides start as nucleoside ____________________ (like ______) • Lose two phosphate groups, energy drives nucleotide joining • The two DNA strands are _________________: sugar and phosphate sides run in opposite directions. One side has 5prime on top and 3 prime on bottom, other has 3prime on top and 5prime on bottom.

  6. Elongation • DNA polymerase adds nucleotides ONLY to the ________ end of a growing DNA strand. New DNA always elongates in the ____ to ____ direction. • Leading strand: DNA polymerase adds in the _____ to ____ direction, goes with the fork. • Lagging strand: DNA polymerase makes short segments in the ____ to ____ direction called ____________ fragments (100-200 bases long); fragments are joined by __________________. • http://www.youtube.com/watch?v=teV62zrm2P0

  7. Priming DNA synthesis • DNA polymerases can only add to existing polynucleotides, can’t start one. • ___________: about 10 nucleotides of RNA that are joined by the enzyme ___________; are eventually replaced by DNA. • _____ primer for the leading strand; one primer for EACH Okazaki fragment in the ________________________.

  8. DNA Repair • Mismatch: DNA polymerase proofreads, other proteins proofread as well. • Repair of existing DNA is called excision repair: _______________(DNA cutting enzyme) cuts out the damaged section, DNA polymerase and ligase add new nucleotides to refill area. Ex. Thymine dimers caused by UV radiation.

  9. Ending Replication • DNA polymerases can’t complete 5 prime ends; DNA strands would shorten over time. • Eukaryotes: ___________ at ends. Multiple repetitions of sequence, usually TTAGGG (no genes) • _________________: enzyme that lengthens telomeres; has RNA along with its proteins • Telomerase may be in cancer cells, giving them immortality.

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