2. POINT > Explain how the structure of DNA makes replication possible POINT > Show how synthesis of new DNA strands is directional POINT > Describe the formation of Okazaki fragments POINT > Identify some of the key enzymes in the replication process

3. POINT > Explain how the structure of DNA makes replication possible Recall that nucleotide base pairing is very specific between two complementary DNA strands: A – T and G - C

4. Adenine always hydrogen bonds with thymine (A-T) Guanine always hydrogen bonds with cytosine (G-C) POINT > Explain how the structure of DNA makes replication possible

5. During DNA replication the two strands are separated. Then other nucleotides fill in, A with T G with C This creates two new DNA strands

6. POINT > Explain how the structure of DNA makes replication possible

7. WB CHECK: What kind of bonds have to be broken to separate the two strands of a DNA molecule? How many sugar-phosphate backbones does a double-stranded DNA molecule have?

8. The original DNA molecule unwinds, and two new daughter strands are built, using the original strands as templates POINT > Explain how the structure of DNA makes replication possible 5’TAGCCTGATCGTATC3’ 3’ATCGGACTAGCATAG5’ Complementary strands in a DNA molecule 5’TAGCCTGATCGTATC3’ 3’ATCGGACTAGCATAG5’ The two DNA strands are separated 5’TAGCCTGATCGTATC3’ 3’ATCGGACTAGCATAG5’ 5’TAGCCTGATCGTATC3’ 3’ATCGGACTAGCATAG5’ Complementary nucleotides are incorporated into new DNA stran ds

9. 5’TAGCCTGATCGTATC3’ 3’ATCGGACTAGCATAG5’ 5’TAGCCTGATCGTATC3’ 3’ATCGGACTAGCATAG5 POINT > Explain how the structure of DNA makes replication possible The original DNA molecule strands are not conserved intact together However, the two original strands are intact as part of new DNA molecules We call this semi-conservative replication

10. POINT > Explain how the structure of DNA makes replication possible  Replication Fork

11. WB CHECK: “Semi-conservative” replication means that a) both new DNA molecules have one strand from the original molecule b) both new DNA molecules have two strands from the original molecule c) both new DNA molecules are made from scratch with new nucleotides

12. POINT > Show how synthesis of a new DNA strand is directional New strands of DNA (or RNA) are only synthesized in the 5’ >> 3’ direction

13. POINT > Show how synthesis of a new DNA strand is directional The 5’ >> 3’ direction of synthesis means that 1 strand is “leading” and 1 strand is “lagging”

14. POINT > Describe the formation of Okazaki fragments The 5’ >> 3’ direction of synthesis results in the formation of Okazaki fragments: short DNA pieces

15. POINT > Describe the formation of Okazaki fragments The 5’ >> 3’ direction of synthesis results in the formation of Okazaki fragments: short DNA pieces

16. POINT > Show how synthesis of a new DNA strand is directional Because DNA molecules are so long (millions of base pairs) replication starts at lots of different sites along the length of the DNA molecule This causes replication bubbles

17. WB CHECK: Okazaki fragments appear a) on both new DNA strands b) only on the leading strand c) only on the lagging strand

18. WB CHECK: Okazaki fragments appear because a) the new nucleotides get added on too fast b) the replication fork opens too slowly c) DNA can only be made in a 5` >> 3` direction d) DNA can only be made in a 3` >> 5` direction

19. WB CHECK: DNA molecules are very long. It would be impossible to get replication done if you just started at one end of the DNA. So, DNA replication starts at many different points along the DNA molecule. This results in a) Okazaki fragments b) replication bubbles c) mutations d) semi-conservative replication

20. POINT > Identify some of the key enzymes in the replication process

21. Helicase – responsible for unwinding the DNA ahead of the replication fork DNA Polymerase – responsible for adding the new and correct nucleotides to the growing strands DNA Ligase – responsible for patching the Okazaki fragments together (the gaps in the sugar-phosphate backbone)

23. WB CHECK: The enzyme responsible for “patching” the sugar- phosphate backbone between Okazaki fragments is a) helicase b) DNA ligase c) DNA polymerase d) RNA polymerase

24. WB CHECK: The enzyme responsible separating the two original DNA strands and creating the replication fork is a) helicase b) DNA ligase c) DNA polymerase d) RNA polymerase

25. WB CHECK: DNA polymerase a) adds new nucleotides in a 5` >> 3` direction b) unwinds the DNA at the replication fork c) builds the new DNA strands d) patches together Okazaki fragments e) a and b f) a and c g) b and c

26. Homework: Read Pages 350-353 Assess page 353 #1-2 Workbook pages 209-211