1. DNA Replication

2. Synthesis Phase (S phase)
S phase in interphase of the cell cycle.
Nucleus of eukaryotes
Mitosis
-prophase
-metaphase
-anaphase
-telophase G1 G2 S
phase
interphase
DNA replication takes
place in the S phase.

3. DNA Nucleotide O O=P-O N CH2 O C1 C4 C3 C2 Phosphate Group
Nitrogenous base
(A, G, C, or T)
CH2 O C1 C4 C3 C2 5
Sugar
(deoxyribose)

4. Figure 11.7 Base Pairing in DNA Is Complementary

5. DNA Replication DNA must replicate during each cell division
THREE alternative models for DNA replication were hypothesized:
Semiconservative replication
Conservative replication
Dispersive replication

6. Meselson and Stahl’s experiment proved replication of DNA to be semiconservative
- See Practical
- See pages  
Figure 11.8

7. Watson & Crick predicted that each DNA strand could serve as a template for the replication of a new strand
Q: What is the mode of replication?

8. The Mechanism of DNA Replication
DNA replication is catalyzed by DNA polymerase
DNA polymerase needs an RNA primer
DNA polymerase adds nucleotides to the 3’ end of the growing strand
Nucleotides are added by complementary base pairing with the template strand

9. Figure 11.11

10. The Mechanism of DNA Replication
Many proteins assist in DNA replication
DNA helicases unwind the double helix, the template strands are stabilized by other proteins

11. Figure 11.16

12. The Mechanism of DNA Replication
Many proteins assist in DNA replication
DNA helicases
RNA primase catalyzes the synthesis of short RNA primers, to which nucleotides are added.
DNA polymerase III extends the strand in the 5’-to-3’ direction

13. RNA primase
Figure 11.15

14. The Mechanism of DNA Replication
DNA synthesis on the leading strand is continuous. It reads the template in the 3’-to -5’ direction (the same direction as helicase)
The lagging strand grows in the opposite direction to the Replication Fork. DNA is always made in the 5’-to-3’ direction.
Therefore, DNA synthesis on the lagging strand is discontinuous
DNA is created as short fragments (Okazaki fragments) that are subsequently ligated together

15. Figure 11.17

16. The Mechanism of DNA Replication
Many proteins assist in DNA replication
DNA helicases
RNA primase
DNA polymerase III
DNA polymerase I degrades the RNA primer and replaces it with DNA
DNA ligase joins the DNA fragments into a continuous daughter strand

17. Figure 11.18

18. Figure 11.8 a

19. DNA Replication Animations
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