1. DNA Replication: A Closer Look
The copying of DNA is remarkable in its speed and accuracy
More than a dozen enzymes and other proteins participate in DNA replication
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2. Animation: Origins of Replication
Getting Started
Replication begins at special sites called _____________________, where the two DNA strands are separated, opening up a ______________________
Animation: Origins of Replication
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3. Parental (template) strand
Fig a
Origin of replication
Parental (template) strand
Daughter (new) strand
Replication fork
Double-stranded DNA molecule
Replication bubble
0.5 µm
Two daughter DNA molecules
Figure Origins of replication in E. coli and eukaryotes
(a) Origins of replication in E. coli

4. Double-stranded DNA molecule
Fig b
Origin of replication
Double-stranded DNA molecule
Parental (template) strand
Daughter (new) strand
0.25 µm
Bubble
Replication fork
Figure Origins of replication in E. coli and eukaryotes
Two daughter DNA molecules
(b) Origins of replication in eukaryotes

5. Single-strand binding protein Topoisomerase Primer Primase
Replication fork
Helicases
Single-strand binding protein
Topoisomerase
Primer
Primase
Have students look at Fig16.13 and specify functions of each term.
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6. Single-strand binding proteins
Fig
Primase
Single-strand binding proteins 3
Topoisomerase 5 3
RNA primer
Figure Some of the proteins involved in the initiation of DNA replication 5 5 3
Helicase

7. STOPPED HERE!

8. Synthesizing a New DNA Strand
Enzymes called ___________________ catalyze the elongation of new DNA at a replication fork
Most DNA polymerases require a _________ and a ________________
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9. Nucleoside triphosphate
Fig
New strand 5 end
Template strand 3 end
5 end
3 end
Sugar A T A T
Base
Phosphate C G C G G C G C
DNA polymerase
3 end A T A
Figure Incorporation of a nucleotide into a DNA strand T
3 end C
Pyrophosphate C
Nucleoside triphosphate
5 end
5 end

10. Antiparallel Elongation
DNA has an antiparallel structure
DNA polymerases add nucleotides only to the free 3end of a growing strand; therefore, a new DNA strand can elongate only in the 5 to 3direction
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11. Overall directions of replication
Fig
Overview
Origin of replication
Leading strand
Lagging strand
Primer
Lagging strand
Leading strand
Overall directions of replication
Origin of replication 3 5
RNA primer 5
“Sliding clamp” 3 5
DNA poll III
Parental DNA
Figure Synthesis of the leading strand during DNA replication 3 5 5 3 5

12. Overall directions of replication
Fig
Overview
Origin of replication
Leading strand
Lagging strand
Lagging strand 2 1
Leading strand
Overall directions of replication 3 5 5 3
Template strand 3
RNA primer 3 5 1 5
Okazaki fragment 3 5 3 1 5 5 3 3
Figure 16.6 Synthesis of the lagging strand 2 1 5 3 5 3 5 2 1 5 3 3 1 5 2
Overall direction of replication

13. Overall directions of replication
Fig a
Overview
Origin of replication
Leading strand
Lagging strand
Lagging strand 2 1
Leading strand
Figure 16.6 Synthesis of the lagging strand
Overall directions of replication

14. Figure 16.6 Synthesis of the lagging strand
Fig b1 3 5 5 3
Template strand
Figure 16.6 Synthesis of the lagging strand

15. Figure 16.6 Synthesis of the lagging strand
Fig b2 3 5 5 3
Template strand 3 5
RNA primer 3 1 5
Figure 16.6 Synthesis of the lagging strand

16. Figure 16.6 Synthesis of the lagging strand
Fig b3 3 5 5 3
Template strand 3 5
RNA primer 3 1 5 3
Okazaki fragment 5 3 1 5
Figure 16.6 Synthesis of the lagging strand

17. Figure 16.6 Synthesis of the lagging strand
Fig b4 3 5 5 3
Template strand 3 5
RNA primer 3 1 5 3
Okazaki fragment 5 3 5 1 3 5 3 2 1 5
Figure 16.6 Synthesis of the lagging strand

18. Figure 16.6 Synthesis of the lagging strand
Fig b5 3 5 5 3
Template strand 3 5
RNA primer 3 1 5 3
Okazaki fragment 5 3 5 1 3 5 3 2 1 5 5 3
Figure 16.6 Synthesis of the lagging strand 3 5 2 1

19. Figure 16.6 Synthesis of the lagging strand
Fig b6 3 5 5 3
Template strand 3 5
RNA primer 3 1 5 3
Okazaki fragment 5 3 5 1 3 5 3 2 1 5 5 3
Figure 16.6 Synthesis of the lagging strand 3 5 2 1 5 3 3 1 5 2
Overall direction of replication

20. Table 16-1

21. Single-strand binding protein Overall directions of replication
Fig
Overview
Origin of replication
Leading strand
Lagging strand
Leading strand
Lagging strand
Single-strand binding protein
Overall directions of replication
Helicase
Leading strand 5
DNA pol III 3 3
Primer
Primase 5
Parental DNA 3
Figure A summary of bacterial DNA replication
DNA pol III
Lagging strand 5
DNA pol I
DNA ligase 4 3 5 3 2 1 3 5

22. Proofreading and Repairing DNA
DNA polymerases proofread newly made DNA, replacing any incorrect nucleotides
Mismatch repair: ______________________________________________________________________________
Nucleotide excision repair: ______________________________________________________________________________
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23. Nuclease DNA polymerase DNA ligase Fig. 16-18
Figure Nucleotide excision repair of DNA damage
DNA ligase

24. Replicating the Ends of DNA Molecules
Limitations of DNA polymerase create problems for the linear DNA of eukaryotic chromosomes
The usual replication machinery provides no way to complete the 5 ends, so repeated rounds of replication produce shorter DNA molecules
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25. Figure 16.19 Shortening of the ends of linear DNA molecules5
Ends of parental DNA strands
Leading strand
Lagging strand 3
Last fragment
Previous fragment
RNA primer
Lagging strand 5 3
Parental strand
Removal of primers and replacement with DNA where a 3 end is available 5 3
Second round of replication
Figure Shortening of the ends of linear DNA molecules 5
New leading strand 3
New lagging strand 5 3
Further rounds of replication
Shorter and shorter daughter molecules

26. Eukaryotic chromosomal DNA molecules have at their ends nucleotide sequences called _______________________
Telomeres do not prevent the shortening of DNA molecules, but they do postpone the erosion of genes near the ends of DNA molecules
It has been proposed that the shortening of telomeres is connected to aging
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27. Fig
Figure Telomeres
1 µm

28. ________________– cells that make gametes in the ovaries and testes
What would happen if chromosomes of germ cells became shorter with every cell cycle?
An enzyme called ________________ catalyzes the lengthening of telomeres in germ cells
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29. The shortening of telomeres might protect cells from cancerous growth by limiting the number of cell divisions
There is evidence of telomerase activity in cancer cells, which may allow cancer cells to persist
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30. How DNA is packaged

31. You should now be able to:
Describe the contributions of the following people: Griffith; Avery, McCary, and MacLeod; Hershey and Chase; Chargaff; Watson and Crick; Franklin; Meselson and Stahl
Describe the structure of DNA
Describe the process of DNA replication; include the following terms: antiparallel structure, DNA polymerase, leading strand, lagging strand, Okazaki fragments, DNA ligase, primer, primase, helicase, topoisomerase, single-strand binding proteins
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32. Describe the function of telomeres
Compare a bacterial chromosome and a eukaryotic chromosome
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