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16.2 DNA Replication

16.2 DNA Replication. DNA in Prokaryotes and Eukaryotes. Prokaryotes: ring of chromosome holds nearly all of the cell’s genetic material. DNA in Prokaryotes and Eukaryotes. Eukaryotes much larger chromosomes 1000 times more DNA than prokaryotes Found in cell’s nucleus Chromosomes

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16.2 DNA Replication

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  1. 16.2 DNA Replication

  2. DNA in Prokaryotes and Eukaryotes • Prokaryotes: • ring of chromosome • holds nearly all of the cell’s genetic material

  3. DNA in Prokaryotes and Eukaryotes • Eukaryotes • much larger chromosomes • 1000 times more DNA than prokaryotes • Found in cell’s nucleus • Chromosomes • Humans: 46 chromosomes • Drosophila melanogaster: 8 chromosomes

  4. DNA Replication Overview • http://www.dnatube.com/video/365/DNA-Replication

  5. DNA Replication Overview • DNA splits into two strands • Complementary base pairs fill in (A with T, C with G) • Left with two DNA molecules • Semiconservative model • One original and one new strand make up a new DNA molecule • Identical

  6. Prokaryote DNA Replication • DNA replication begins at a single point and continues to replicate whole circular strand • Replication goes in both directions around the DNA (begins with replication fork)

  7. Layout of the Eukaryote DNA • Two DNA strands are antiparallel • Run in opposite directions • 3’ (three prime) – 5’ (five prime) • 5’ (five prime) – 3’ (three prime)

  8. Eukaryote DNA Replication • Begins in hundreds of locations along the chromosome • Origins of replication

  9. Initiation of DNA Replication • Begins when the DNA molecule “unzips” • Replication fork • Replication “bubble” • Hydrogen bonds between base pairs breaks • Helicase • Single-strand binding proteins • Topoisomerase – relieves pressure of DNA ahead of replication fork

  10. Synthesis of a New DNA Strand • Each strand serves as a template for a new strand to form • Complimentary bases will attach • DNA polymerase • E. coli – DNA polymerase III and DNA polymerase I • Humans – 11 different DNA polymerase molecules

  11. Synthesis of a New DNA Strand • RNA primer • Nucleoside triphosphate • As each nucleotide is added to the new strand, 2 phosphates are lost • Hydrolysis releases energy to drive reaction

  12. Synthesis of a New DNA Strand • Antiparallel Elongation • Remember 3’ – 5’ and 5’ – 3’ • Replication in the 3’ to 5’ direction ONLY • MEANING the NEW strand of DNA will form starting with the 5’ end • Leading strand (only 1 primer needed – moves toward the replication fork) • Lagging strand (many primers needed – moves away from replication fork)

  13. Important Enzymes • Helicase, single-strand binding protein, topoisomerase • Primase • Synthesis of RNA primer • DNA polymerase III (DNA pol III) • Add new bases to DNA strand • DNA polymerase I (DNA pol I) • Removes and replaces RNA primer from 5’ end • DNA ligase • Links Okazaki fragments and replaces RNA primer from 3’ end

  14. The Finished Product • Each DNA molecule has one original strand and one new strand • Molecules are identical

  15. Repair of DNA • DNA polymerase • Proofreads and repairs damaged/mismatched DNA • Nuclease • Removes section of DNA that is damaged • DNA polymerase and DNA ligase replace missing portion

  16. Telomeres • Found at the ends of each chromosome • Contain no genes • Sequence that can be cut short and will not affect normal functioning • TTAGGG • Telomerase lengthens telomeres in gametes

  17. 16.3 A chromosome consists of a DNA molecule packed together with proteins

  18. Chromosomes

  19. Chromosome Structure • DNA in bacteria - nucleoid • Chromosomes contain both DNA and protein to form chromatin

  20. Chromosome Structure • Chromatin is DNA coiled around histones (protein) • Heterochromatin – present in interphase, slightly condensed into clumps • Euchromatin – uncondensed chromatin (“true chromatin”)

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