12-2

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DNA replication

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12-2

  1. 1. 12-2 chromosomes and DNA replication• DNA: – Prokaryotic cell: • Naked, in cytoplasm, no nucleus • Single circular DNA • No complex with histone Bases on the chromosome – eukaryotic cell: • In nucleus, • In the form of chromosome Chromosome E. coli bacterium
  2. 2. • Chromosome structure: – Chromatin : DNA + proteins – Chromosome : supercoiled chromatin – Nucleosome • beadlike structures in chromosome formed by DNA and histone molecules • Help to fold long DNA into tiny cell nucleus Chromosome Nucleosome DNA double helix Coils Supercoils Histones
  3. 3. • DNA replication (in interphase of mitosis or meiosis) – Prokaryotic cell: • Begins at a single point • Proceeds in two directions
  4. 4. • DNA replication (in interphase of mitosis or meiosis) – Eukaryotic cell: • Begins at many sites • Proceeds in two directions
  5. 5. • DNA replication – Semi-conservative replication • During DNA replication, the DNA double helix separates into two strands. Each strand serves as a template to produces two new complementary strands following the rules of base pairing. Parent DNA Copy
  6. 6. • DNA replication – Steps • Unzip (form replication fork) • Strands assembled in the 5’ to 3’ direction (Continuous and Discontinuous, form okazaki fragments) • 2 identical DNA molecules replication forkAHL
  7. 7. AHL
  8. 8. • DNA replication – Enzyme envolved Helicase: unzips DNA. Primase: add short RNA primers. Single-strand binding protein : hold seperated strands apart DNA polymerase : DNA polIII: attaches complementary nucleotides & proofreading DNA pol I: replaces RNA primers with DNA nucleotides. DNA ligase: seal okazaki fragmentsAHL
  9. 9. AHL

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