1. DNA Structure and Replication

2. Figure 16.5 The double helix

3. DNA Q’s – Use diagram in previous slide 1.Which diagrams show the double helix structure? 2.Examine Figure (b). It looks like a ladder. What two parts of a nucleotide form the sides (uprights) of the ladder? 3.Examine Figure (b) again. What part of a nucleotide forms the steps of the ladder? 4.Look at Figure (a). Determine the number of adenine, guanine, cytosine, and thymine nucleotides. Write them down. What do you notice about the numbers? 5.What connects the two strands of DNA? 6.What holds the nucleotides on the individual strands together? 7.How are the two ends of each strand different?

4. This slide shows how the pairing keeps the DNA double helix width uniform

5. This slide reviews complementary base pairing. Which pair makes more hydrogen bonds?

6. What happens if the DNA is not copied exactly or entirely? If not exactly, the sequence of bases will be different which could affect the organism because the different sequence would change the gene. Recall from the DNA Scissors lab that a gene is a segment of DNA that controls a trait. If not all is copied, some of the bases will be missing and the organism could lose some important sequence that controls all its life activities.

7. Figure 16.7 A model for Semiconservative DNA Replication Click on the next few slides to view a simplistic version of DNA replication

8. Figure 16.7 A model for DNA replication: the basic concept (Layer 2)

9. Figure 16.7 A model for DNA replication: the basic concept (Layer 3)

10. Figure 16.7 A model for DNA replication: the basic concept (Layer 4)

11. DNA replication begins at specific sites called origins of replication. There are (6) origins below. Figure 10.5A Parental strand Origin of replication Bubble Two daughter DNA molecules Daughter strand DNA Replication: A closer look More bubbles, faster the replication process

12. Figure 16.10 Origins of replication in eukaryotes

13. Each strand of the double helix is oriented in the opposite direction This directionality causes the daughter strands to grow in opposite directions. The new strand always grows in a 5’  3’ direction. Figure 10.5B 5 end3 end 5 end P P P P P P P P Directionality of DNA

14. LE 16-13 New strand 5 end Phosphate Base Sugar Template strand 3 end 5 end 3 end 5 end 3 end 5 end 3 end Nucleoside triphosphate DNA polymerase Pyrophosphate DNA Replication with Adding a Nucleotide Notice how after we added the Thymine nucleotide to the new strand, the 3’ end still exists and is ready for another nucleotide. What would it be?

15. How DNA daughter strands are synthesized 5 end P P Parental DNA Figure 10.5C DNA polymerase molecule 5 3 3 5 3 5 Daughter strand synthesized continuously Daughter strand synthesized in pieces DNA ligase Overall direction of replication 5 3 The daughter strands are identical to the parent molecule Replication

16. Enzymes of Replication Helicase – causes the DNA to unwind and open DNA polymerase III – allows for the adding of a nucleotide to the 3’ –OH end of the daughter strand Ligase – allows for the short DNA fragments to be joined to form one continuous piece of DNA Topoisomerase – enzyme that prevents the open DNA from twisting RNA primase – enzyme that puts the first nucleotide down to start the daughter strand

17. Proving DNA Replication is Semiconservative The next few slides illustrate the famous Messleshon and Stahl experiment. You are not responsible for understanding it for Honors Biology. Be able to describe the difference between semiconservative, conservative and dispersive replication.

18. Figure 16.8 Three alternative models of DNA replication

19. Figure 16.9 The Meselson-Stahl experiment tested three models of DNA replication (Layer 1)

20. Figure 16.9 The Meselson-Stahl experiment tested three models of DNA replication (Layer 2)

21. Figure 16.9 The Meselson-Stahl experiment tested three models of DNA replication (Layer 3)

22. Figure 16.9 The Meselson-Stahl experiment tested three models of DNA replication (Layer 4)

23. Adding Nucleotide Animation DNA Replication Animation