DNA Replication and Transcription: Biosynthesis of DNA and RNA 阮雪芬

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1 DNA Replication and Transcription: Biosynthesis of DNA and RNA 阮雪芬

2 Outline Introduction Replication of DNA Action of DNA Polymerases DNA Damage and Repair Synthesis of RNA Post-transcriptional Modification of RNA Base Sequences in DNA

3 Outline Introduction Replication of DNA Action of DNA Polymerases DNA Damage and Repair Synthesis of RNA Post-transcriptional Modification of RNA Base Sequences in DNA

4 Introduction Replication Templates Repair

5 Outline Introduction Replication of DNA Action of DNA Polymerases DNA Damage and Repair Synthesis of RNA Post-transcriptional Modification of RNA Base Sequences in DNA

6 Characteristics of the Replication Process DNA Replication is Semiconservative Replication Begins at a Discrete Point on DNA

7 Two Possible Models for DNA Replication X

8 Density Gradient Centrifugation Matthew Meselson and Franklin Stahl

9 Preliminary Experiment

10 Actual Experiment

11 Replication Begins at a Discrete John Cairns, 1950 Point on DNA Replication fork Replication fork

12 The Theta Model for Replication of a Circular DNA Molecule In prokaryotes

13 Proposed Pathway fro Replication of Eukaryotic DNA

14 Outline Introduction Replication of DNA Action of DNA Polymerases DNA Damage and Repair Synthesis of RNA Post-transcriptional Modification of RNA Base Sequences in DNA

15 DNA Polymerase I Was isolated from E. coli, in 1957 dntp + (dnmp) n d(ntp ) n+1 + PPi

16 The Action of DNA Polymerase

18 Exonuclease Activity of DNA Acts as a proofreading and repair enzyme by catalyzing hydrolytic removal of mismatched bases. Polymerase I

19 5 3 Exonuclease Activity

20 Okazaki Fragments

21 Complete Scheme Showing Sequential Steps of Replication Helicase Process DNA gyrase: topoisomerase Formation of Replication fork

22 Single-stranded DNA Binding Proteins

23 Initiation of DNA Synthesis Primase

24 DNA Polymerase III

25 DNA Polymerase I

26 DNA Ligase

27 DNA Ligase

29 Eukaryotic Chromosomes and Telomeres Telomere: The repeating sequence AGGGTT Telomerase: catalyzes the synthesis of these DNA ends Telomerase becomes activated in human cancer cells

30 Outline Introduction Replication of DNA Action of DNA Polymerases DNA Damage and Repair Synthesis of RNA Post-transcriptional Modification of RNA Base Sequences in DNA

31 Mutations Spontaneous mutations Induced mutations

32 Spontaneous mutations Those changes that occur during normal genetic and metabolic functions in the cell. Two major types: Mismatching of base pairs: one for every base pairs incorporated Base modifications caused by hydrolytic reactions

33 Spontaneous mutations Are favorable in that they confer a selective advantage to an organism. The causes of evolutionary processes Replication errors are of three types Substitution Insertion Deletion

34 The Basic Repair Mechanism for Mismatched Base Pairs in E. coli

35 Mutagenic Damage to DNA Caused by Spontaneous Processes DNA glycosidases

36 Induced mutations Mutagens Ionizing radiation Chemicals Heterocyclic base analogs Reactive chemical mutagens Intercalating agents

37 Ionizing radiation: Hydroxyl Radical

38 Chemical Mutagens Heterocyclic base analogs

39 Alkylating Agents

40 Alkylating Agents

41 Intercalating Agents

42 Binding of Intercalating Agents to Ames test DNA

43 Outline Introduction Replication of DNA Action of DNA Polymerases DNA Damage and Repair Synthesis of RNA Post-transcriptional Modification of RNA Base Sequences in DNA

44 Transcription

45 Initiation of Transcription

46 Elongation of the RNA Chain in Transcription

47 Termination of Transcription

48 Hairpin Loop

49 Inhibitors of Transcription

50 RNA-directed RNA Synthesis RNA replicase No editing, proofreading, or repair activities

51 Outline Introduction Replication of DNA Action of DNA Polymerases DNA Damage and Repair Synthesis of RNA Post-transcriptional Modification of RNA Base Sequences in DNA

52 Post-transcriptional Modification of trna in E. coli

53 mrna Processing Capping Poly A addition Splicing coding sequences

54 Capping Reactions

55 Poly A Addition 20 ~250 n Catalyzed by polyadenylate polymerase Increasing resistance to cellular nucleases

56 Splicing Coding Sequences

57 Outline Introduction Replication of DNA Action of DNA Polymerases DNA Damage and Repair Synthesis of RNA Post-transcriptional Modification of RNA Base Sequences in DNA

58 2, 3 -Dideoxyribonucleoside Triphosphates

59 Sanger Chain-termination Method

60 Exercises 11.1 a, c, d, f, k, l, m, n, s

DNA replication: Enzymes link the aligned nucleotides by phosphodiester bonds to form a continuous strand.

DNA replication: Enzymes link the aligned nucleotides by phosphodiester bonds to form a continuous strand. DNA replication: Copying genetic information for transmission to the next generation Occurs in S phase of cell cycle Process of DNA duplicating itself Begins with the unwinding of the double helix to expose