1. DNA Replication
Essential Question: How do enzymes help ensure DNA is copied correctly?

2. Why does DNA replicate?
Cells copy genetic information before cell division so that each new cell has a complete set of DNA
DNA replication occurs in the nucleus…WHY??

3. DNA Template

4. How does DNA replicate
1) UNWIND: Topoisomerase unwinds the coiled strands of DNA

5. 2) UNZIP: DNA Helicase “unzips” the strands of DNA breaking the hydrogen bonds

6. 3) HOLD OPEN: Single-Strand Binding proteins (SSBs) keep strands separated

7. 4) BASE PAIRING: DNA polymerase III bonds free floating nucleotides with nucleotides from the parent strand using base pairing rules

8. Direction of Replication
DNA polymerase can only build in the 5’ to 3’ direction
RNA
Primer
DNA Polymerase
Nucleotide 5’ 3’
Direction of Replication
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9. Synthesis of the New DNA Strands
The Lagging Strand is synthesized discontinuously against overall direction of replication
This strand is made in MANY short segments It is replicated from the replication fork toward the origin
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10. Lagging Strand Segments
Okazaki Fragments - series of short segments on the lagging strand
Must be joined together by an enzyme
Lagging Strand
RNA
Primer
DNA
Polymerase 3’ 5’
Okazaki Fragment
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11. 6) PROOFREAD:
DNA Polymerase I proofreads new strand and backtracks to correct errors

12. 5) JOINING NUCLEOTIDES: DNA ligase bonds those nucleotides and okazaki fragments together.

13. The result is 2 identical DNA molecules.

14. Each w/1 new strand & 1 old strand
Called Semi-conservative replication

16. (Continuous Replication)
(Place where replication begins)
(Replication starts & stops)

19. DNA Replication Animation

20. Talk to a Partner

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Question:
What would be the complementary DNA strand for the following DNA sequence?
DNA 5’-CGTATG-3’
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23. copyright cmassengale
Answer:
DNA 5’-CGTATG-3’
DNA 3’-GCATAC-5’
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