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Ch. 12.2: Replication of DNA

Ch. 12.2: Replication of DNA. Section objective: Summarize DNA replication. Replication of DNA. Before a cell can divide by mitosis or meiosis, it must first make a copy of its chromosomes. The DNA in the chromosomes is copied in a process called DNA replication .

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Ch. 12.2: Replication of DNA

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  1. Ch. 12.2: Replication of DNA • Section objective: • Summarize DNA replication

  2. Replication of DNA • Before a cell can divide by mitosis or meiosis, it must first make a copy of its chromosomes. • The DNA in the chromosomes is copied in a process called DNA replication. • Without DNA replication, new cells would have only half the DNA of their parents. • DNA is copied during interphase prior to mitosis and meiosis. • It is important that the new copies are exactly like the original molecules.

  3. Replication of DNA • DNA replication depends on specific base pairing • In DNA replication, the strands separate • Enzymes use each strand as a template to assemble the new strands Nucleotides Parental moleculeof DNA Both parental strands serveas templates Two identical daughtermolecules of DNA

  4. Replication of DNA • Semiconservative replication: • Parental strands of DNA separate, serve as templates and produce 2 molecules of DNA that have one strand of parental DNA and one strand of new DNA

  5. Copying DNA • Matching bases allows DNA to be easily copied

  6. DNA replication • DNA Helicase: enzyme responsible for uncoiling the double helix and unzipping the weak hydrogen bonds between the base pairs

  7. DNA replication • Enzyme • DNA polymerase • adds new bases DNA basesin nucleus DNA polymerase

  8. Copying DNA • Build daughter DNA strand • use original parent strand as “template” • add new matching bases • synthesis enzyme = DNA polymerase DNA Polymerase

  9. Replication 3 5 energy DNA Polymerase III • Adding bases • can only add nucleotides to 3 end of a growing DNA strand • need a “starter” nucleotide to bond to • strand only grows 53 DNA Polymerase III energy DNA Polymerase III energy DNA Polymerase III energy 3 5

  10. Leading strand- elongates as DNA unwinds • Lagging strand –elongates in opposite direction . Synthesized discontinuously into small segments called Okazaki fragments • DNA ligase (an enzyme)links these sections

  11. Okazaki ligase 3 3 3 3 3 3 3 5 5 5 5 5 5 5 Leading & Lagging strands Limits of DNA polymerase III • can only build onto 3 end of an existing DNA strand  Okazaki fragments Lagging strand growing replication fork  Leading strand Lagging strand • Okazaki fragments • joined by ligase • “spot welder” enzyme DNA polymerase III Leading strand • continuous synthesis

  12. DNA polymerase DNA polymerase New copies of DNA • Get 2 exact copies of DNA to split between new cells

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