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DNA Replication PowerPoint

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  • 1.IB Topics 3 and 7


  • DNA replication is a means to produce new molecules that have the same base sequence
  • Occurs during interphase of the cell cylce
  • DNA replication is semi-conservative
    • The parent DNA strand separates into two
    • Each strand serves as a template for new complementary strands
    • The new double helix is half original

3. 4.

  • 1. Bacteria were grown in a medium containing nitrogen 15 (N 15 ) for several generation
  • 2. If the medium contains no other nitrogen source, the E. coli will use N 15and incorporate it into their DNA
  • 3. Eventually, they will only have N 15
  • 4. Once the E. coli had only N 15they were put into a growing medium contain only N 14


  • 5. N 15is heavier than N 14making new incorporation of nitrogen easy to distinguish
  • 6. The differences were measured according to the densities of the new strands

6. 7. -Explain what is happening in this diagram.-Which color is N 14 ? N 15 ? -Which model of DNA replication is illustrated? -Why arent there double helices with two red strands in the 2 ndgeneration? 8.

  • Occurs in a 5 -> 3 direction
    • The 5 end of the new nucleotide attached to the 3 end of the nucleotide before it
  • DNA is unwound and unzipped by the enzymehelicase
  • DNA polymerase IIIcreates links between the nucleotides
    • It creates a strand that is complementary to the original strand)


  • Replication takes place at several places on one double helix at the same time
  • Once the double helix is unwound and unzipped the two parent strands become the leading and lagging strands
  • This happens because the strands are antiparallel

3 5 3 5 10. DNA Replication (the lagging strand)

  • The lagging strand runs from 3 to 5
  • 1. Before DNA replication begins there must be and RNA primer
  • 2. The RNA primer is made by adding complimentary RNA nucleotides to the lagging DNA strand by hydrogen bonding of the bases
    • RNA has uracil instead of thymine
  • 3. RNA primase(an enzyme) then bonds the RNA nucleotides together

3 5 RNA primase RNA primer 11.

  • 4. After RNA primer is in place DNA nucleotides are added by DNA polymerase III
  • 5. Eventually, the segment of DNA will run into another RNA primer
  • 6. The DNA segments are called Okazaki fragments

DNA Replication (the lagging strand) 3 5 RNA primer DNA polymerase III Okazaki fragment 12.

  • 7. Once Okazaki fragments are formed DNA polymerase I replaces the RNA primer with DNA nucleotides
  • 8. DNA ligase links the fragments together

DNA Replication (the lagging strand) 3 5 3 5 Parent strand New strand 13.

  • In the lagging strand DNA replication is discontinuous
  • DNA is replicated in segments that become joined together

DNA Replication (the lagging strand) 14. DNA replication (the leading strand)

  • Replication is continuous
  • There are no fragments
  • Helicase unwinds and unzips the double helix
  • DNA polymerase III adds nucleotides in the direction of 5 ->3
    • DNA polymerase only works in the direction of5 ->3

15. DNA replication (a quick review)

  • Lagging strand
    • Formed in short segment of 100-200 nucleotides (these are the Okazaki fragments)
    • Grows in direction of 5 ->3 because DNA polymerase III only works in the5 ->3
    • 1. Helicase unwinds and unzips the parent DNA
    • 2.RNA primer is formed by RNA nucleotides that are joined together by RNA primase
    • 3. DNA polymerase III bonds DNA nucleotides to the RNA primer
    • 4. DNA polymerase I replaces the RNA primer with DNA nucleotides
    • 5. DNA ligase joins the Okazaki fragments together
  • Leading strand
    • 1. Helicase unwinds and unzips
    • 2. DNA polymerase III adds complimentary DNA nucleotides

16. Putting it all together The leading and lagging strand are determined by the 5 and 3 end of the strand. 5 5 3 3 Which template will be the leading strand? 17. 5 5 3 3 18. DNA Replication (Animations)

  • McGraw Hill

19. Assignment

  • Explain DNA replication.
  • Use p. 284-289 to help you.
  • Include drawings and annotations to aid your explanation.

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