1. Ch20 and 21 DNA, Synthesis and Repair 阮雪芬NTU April 29, 2003

2. What is Nucleic Acids?

3. Ribose and deoxyribose

4. Purines and Pyrimidines

6. Backbones of DNA and RNA sugar phosphate

7. Hydrogen Bond in Watson-Crick Base Pairs

8. Structure of a DNA Chain

9. Spontaneous Hybridization

10. DNA Structure X

11. Watson-Crick Model of Double- Helical DNA

12. Minor and Major Groove

13. Two Antiparallel Strands of DNA

14. How is the DNA Packaged Into A Nucleus Winding around nucleosomes Nucleosomes packed The fibres form loops The loops form other coils and/or folds

15. EM of a 30 nm Fibre of Chromatin

16. Electron Micrographs of Circular DNA from Mitochondria

17. Chromosome

18. DNA Synthesis and Repair

19. Semiconservative DNA Replication

20. Bidirectional Replication of E. coli Chromosome Very rich in A-T pairs helicase

21. Multiple Bidirectional Replicative Forks in a Eukaryotic Chromosome

22. The Eukaryotic Cell Cycle

23. Supercoil Formation

24. The Reaction Catalysed by Type I Topoisomerase Breaks one strand of a supercoiled double helix Does not require ATP

25. The Reaction Catalysed by Type II Topoisomerase Breaks two strand of a supercoiled double helix Require ATP

26. Summary of E. coli and Eukaryote Topoisomerases TypeAction on DNAEffect on supercoiling Topoisomerase I E. coliCuts one DNA strand Relaxes negative supercoils EukaryotesCuts one DNA strand Relaxes positive and negative supercoils Topoisomerase II E. coliCuts two DNA strand; ATP- dependent Relaxes positive supercoils; insert negative supercoils EukaryotesCuts two DNA strand; ATP- dependent Relaxes positive supercoils but cannot insert negative supercoils

27. The Balancing Act of Gyrase and Topoisomerase I in E. coli

28. A Mechanism by which Eukaryotic DNA Becomes Negatively Supercoiled

29. Polymerization Reaction Catalyzed by DNA Polymerases

30. DNA Replication

31. How Does a New Strand Get Started

32. RNA Polymerase RNA polymerase requires the following components: –A template –Activated precursors –A divalent metal ions RNA polymerase does not require a primer

33. The Polarity Problem in DNA Replication

34. Diagram of A Replicative Fork

35. The Loop Model for Okazaki Fragment Synthesis

36. The Loop Model ATP-driven Single-strand binding protein

37. Ribbon Representations of the Yeast and E. coli Sliding “Clamps” Yeas: trimer E. coli:dimer Sliding clamp is a ring shaped protein structure surrounding the DNA

38. The Step in Loading a Sliding Clamp for DNA Synthesis in E. coli

39. Polymerase I Actions In Processing Okazaki Fragments

40. Events involved in DNA Replication in E. coli and in Eukaryotes

41. Methyl-directed Pathway for Mismatch Repair

42. Repair of DNA Damage in E. coli Direct repair Nucleotide excision repair Base excision repair and AP site repair

43. The Pathway of Nucleotide Excision Repair in E. coli

44. AP Site Formation and Repair

45. The Machinery in the Eukaryotic Replicative Fork In E. coli, polymerase I, II, and III. In eukaryotes, polymerase . –Polymerase  and  : exonuclease –Polymerase  and  : have repair function –Polymerase  : for mitochondrial DNA replication

46. The Shortening of Linear Chromosomes by Replication Telomeric DNA: no informational content

47. Mechanism by Which Telomerase Synthesizes Telomeric DNA TTAGGG sequence Reverse transcriptase Telomerase

48. Tansposons or Jumping Genes

49. Transposon

50. Homologous Recombination

51. Single-strand Invasion This reaction is a test tube model; not involved in the cellular process

52. A Cross-over Junction

53. Meiosis