Presentation is loading. Please wait.

Presentation is loading. Please wait.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CHAPTER 14 LECTURE SLIDES To run the animations you must be.

Similar presentations


Presentation on theme: "Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CHAPTER 14 LECTURE SLIDES To run the animations you must be."— Presentation transcript:

1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CHAPTER 14 LECTURE SLIDES To run the animations you must be in Slideshow View. Use the buttons on the animation to play, pause, and turn audio/text on or off. Please note: once you have used any of the animation functions (such as Play or Pause), you must first click in the white background before you advance the next slide.

2 DNA: The Genetic Material Chapter 14

3 Frederick Griffith – 1928 Studied Streptococcus pneumoniae, a pathogenic bacterium causing pneumonia 2 strains of Streptococcus –S strain is virulent –R strain is nonvirulent Griffith infected mice with these strains hoping to understand the difference between the strains 3

4 4 Griffiths results –Live S strain cells killed the mice –Live R strain cells did not kill the mice –Heat-killed S strain cells did not kill the mice –Heat-killed S strain + live R strain cells killed the mice

5 5

6 6

7 7 Transformation –Information specifying virulence passed from the dead S strain cells into the live R strain cells Our modern interpretation is that genetic material was actually transferred between the cells

8 8 Avery, MacLeod, & McCarty – 1944 Repeated Griffiths experiment using purified cell extracts Removal of all protein from the transforming material did not destroy its ability to transform R strain cells DNA-digesting enzymes destroyed all transforming ability Supported DNA as the genetic material

9 9 Hershey & Chase –1952 Investigated bacteriophages –Viruses that infect bacteria Bacteriophage was composed of only DNA and protein Wanted to determine which of these molecules is the genetic material that is injected into the bacteria

10 10 Bacteriophage DNA was labeled with radioactive phosphorus ( 32 P) Bacteriophage protein was labeled with radioactive sulfur ( 35 S) Radioactive molecules were tracked Only the bacteriophage DNA (as indicated by the 32 P) entered the bacteria and was used to produce more bacteriophage Conclusion: DNA is the genetic material

11 11

12 12 DNA Structure DNA is a nucleic acid Composed of nucleotides –5-carbon sugar called deoxyribose –Phosphate group (PO 4 ) Attached to 5 carbon of sugar –Nitrogenous base Adenine, thymine, cytosine, guanine –Free hydroxyl group (OH) Attached at the 3 carbon of sugar

13 13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Purines Pyrimidines Adenine Guanine NH 2 C C N N N C H N C CH O H H OC NC H N C H C H O O C N C H N C H3CH3C C H H O O C N C H N C H C H C C N N N C H N C CH H Nitrogenous Base 4´4´ 5´5´ 1´1´ 3´3´2´2´ O P O–O– –O–O Phosphate group Sugar Nitrogenous base O CH 2 N N O N NH 2 OH in RNA Cytosine (both DNA and RNA) Thymine (DNA only) Uracil (RNA only) OH H in DNA

14 Phosphodiester bond –Bond between adjacent nucleotides –Formed between the phosphate group of one nucleotide and the 3 OH of the next nucleotide The chain of nucleotides has a 5-to-3 orientation 14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Base CH 2 O 5´5´ 3´3´ O P O OH CH 2 –O–OO C Base O PO 4 Phosphodiester bond

15 Chargaffs Rules Erwin Chargaff determined that –Amount of adenine = amount of thymine –Amount of cytosine = amount of guanine –Always an equal proportion of purines (A and G) and pyrimidines (C and T) 15

16 16 Rosalind Franklin Performed X-ray diffraction studies to identify the 3-D structure –Discovered that DNA is helical –Using Maurice Wilkins DNA fibers, discovered that the molecule has a diameter of 2 nm and makes a complete turn of the helix every 3.4 nm

17 17 James Watson and Francis Crick – 1953 Deduced the structure of DNA using evidence from Chargaff, Franklin, and others Did not perform a single experiment themselves related to DNA Proposed a double helix structure

18 Double helix 2 strands are polymers of nucleotides Phosphodiester backbone – repeating sugar and phosphate units joined by phosphodiester bonds Wrap around 1 axis Antiparallel 18 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 5´5´ 3´3´ P P P P OH 5-carbon sugar Nitrogenous base Phosphate group Phosphodiester bond O O O O 4´4´ 5´5´ 1´1´ 3´3´ 2´2´ 4´4´ 5´5´ 1´1´ 3´3´ 2´2´ 4´4´ 5´5´ 1´1´ 3´3´ 2´2´ 4´4´ 5´5´ 1´1´ 3´3´ 2´2´

19 19

20 Complementarity of bases A forms 2 hydrogen bonds with T G forms 3 hydrogen bonds with C Gives consistent diameter 20 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A H Sugar T G C N H N O H CH 3 H H N N N H N N N H H H N O H H H N NH N N H N N Hydrogen bond Hydrogen bond

21 21 DNA Replication 3 possible models 1.Conservative model 2.Semiconservative model 3.Dispersive model

22 22 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Conservative

23 23 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ConservativeSemiconservative

24 24 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ConservativeSemiconservativeDispersive

25 25 Meselson and Stahl – 1958 Bacterial cells were grown in a heavy isotope of nitrogen, 15 N All the DNA incorporated 15 N Cells were switched to media containing lighter 14 N DNA was extracted from the cells at various time intervals

26 26 Conservative model = rejected –2 densities were not observed after round 1 Semiconservative model = supported –Consistent with all observations –1 band after round 1 –2 bands after round 2 Dispersive model = rejected –1 st round results consistent –2 nd round – did not observe 1 band

27 27

28 28 DNA Replication Requires 3 things –Something to copy Parental DNA molecule –Something to do the copying Enzymes –Building blocks to make copy Nucleotide triphosphates

29 29 DNA replication includes –Initiation – replication begins –Elongation – new strands of DNA are synthesized by DNA polymerase –Termination – replication is terminated

30 30

31 DNA polymerase –Matches existing DNA bases with complementary nucleotides and links them –All have several common features Add new bases to 3 end of existing strands Synthesize in 5-to-3 direction Require a primer of RNA 31 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 5´5´ 3´3´ 5´5´ 5´5´ 5´5´ 3´3´ 3´3´ RNA polymerase makes primerDNA polymerase extends primer

32 Prokaryotic Replication E. coli model Single circular molecule of DNA Replication begins at one origin of replication Proceeds in both directions around the chromosome Replicon – DNA controlled by an origin 32

33 33

34 34 E. coli has 3 DNA polymerases –DNA polymerase I (pol I) Acts on lagging strand to remove primers and replace them with DNA –DNA polymerase II (pol II) Involved in DNA repair processes –DNA polymerase III (pol III) Main replication enzyme –All 3 have 3-to-5 exonuclease activity – proofreading –DNA pol I has 5-to-3 exonuclase activity

35 Unwinding DNA causes torsional strain –Helicases – use energy from ATP to unwind DNA –Single-strand-binding proteins (SSBs) coat strands to keep them apart –Topoisomerase prevent supercoiling DNA gyrase is used in replication 35 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Supercoiling Replisomes No Supercoiling Replisomes DNA gyrase

36 Semidiscontinous DNA polymerase can synthesize only in 1 direction Leading strand synthesized continuously from an initial primer Lagging strand synthesized discontinuously with multiple priming events –Okazaki fragments 36

37 37

38 38 Partial opening of helix forms replication fork DNA primase – RNA polymerase that makes RNA primer –RNA will be removed and replaced with DNA

39 Leading-strand synthesis –Single priming event –Strand extended by DNA pol III Processivity – subunit forms sliding clamp to keep it attached 39

40 Lagging-strand synthesis –Discontinuous synthesis DNA pol III –RNA primer made by primase for each Okazaki fragment –All RNA primers removed and replaced by DNA DNA pol I –Backbone sealed DNA ligase Termination occurs at specific site –DNA gyrase unlinks 2 copies 40

41 41 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 5´ 3´ Primase RNA primer Okazaki fragment made by DNA polymerase III Leading strand (continuous) DNA polymerase I Lagging strand (discontinuous) DNA ligase

42 Replisome Enzymes involved in DNA replication form a macromolecular assembly 2 main components –Primosome Primase, helicase, accessory proteins –Complex of 2 DNA pol III One for each strand 42

43 43 Leading strand Lagging strand Primase Clamp loader Helicase DNA polymerase III DNA gyrase RNA primer Single-strand binding proteins (SSB) RNA primer β clamp 1. A DNA polymerase III enzyme is active on each strand. Primase synthesizes new primers for the lagging strand. 5´ 3´ 5´ 3´ 5´ 3´ RNA primer Loop grows Second Okazaki fragment nears completion First Okazaki fragment 2. The loop in the lagging-strand template allows replication to occur 5´-to- 3´ on both strands, with the complex moving to the left. 5´ 3´ 5´ 3´ 5´ 3´ Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 5´ 3´ 3. When the polymerase III on the lagging strand hits the previously synthesized fragment, it releases the β clamp and the template strand. DNA polymerase I attaches to remove the primer. β clamp releases Lagging strand releases DNA polymerase III DNA polymerase I 5´ 3´ 5´ 3´

44 44 Clamp loader 4. The clamp loader attaches the β clamp and transfers this to polymerase III, creating a new loop in the lagging-strand template. DNA ligase joins the fragments after DNA polymerase I removes the primers. DNA ligase patches nick DNA polymerase I detaches after removing RNA primer 5´ 3´ 5´ 3´ 5´ 3´ New bases 5. After the β clamp is loaded, the DNA polymerase III on the lagging strand adds bases to the next Okazaki fragment. Leading strand replicates continuously Loop grows 5´ 3´ 5´ 3´ 5´ 3´ Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

45 45

46 46 Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the Normal or Slide Sorter views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at

47 47 Eukaryotic Replication Complicated by –Larger amount of DNA in multiple chromosomes – Linear structure Basic enzymology is similar –Requires new enzymatic activity for dealing with ends only

48 48 Multiple replicons – multiple origins of replications for each chromosome –Not sequence specific; can be adjusted Initiation phase of replication requires more factors to assemble both helicase and primase complexes onto the template, then load the polymerase with its sliding clamp unit –Primase includes both DNA and RNA polymerase –Main replication polymerase is a complex of DNA polymerase epsilon (pol ε) and DNA polymerase delta (pol δ)

49 Telomeres Specialized structures found on the ends of eukaryotic chromosomes Protect ends of chromosomes from nucleases and maintain the integrity of linear chromosomes Gradual shortening of chromosomes with each round of cell division –Unable to replicate last section of lagging strand 49

50 50

51 51 Telomeres composed of short repeated sequences of DNA Telomerase – enzyme makes telomere of lagging strand using and internal RNA template (not the DNA itself) –Leading strand can be replicated to the end Telomerase developmentally regulated –Relationship between senescence and telomere length Cancer cells generally show activation of telomerase

52 52

53 53 DNA Repair Errors due to replication –DNA polymerases have proofreading ability Mutagens – any agent that increases the number of mutations above background level –Radiation and chemicals Importance of DNA repair is indicated by the multiplicity of repair systems that have been discovered

54 54 DNA Repair Falls into 2 general categories 1.Specific repair –Targets a single kind of lesion in DNA and repairs only that damage 2.Nonspecific –Use a single mechanism to repair multiple kinds of lesions in DNA

55 55 Photorepair Specific repair mechanism For one particular form of damage caused by UV light Thymine dimers –Covalent link of adjacent thymine bases in DNA Photolyase –Absorbs light in visible range –Uses this energy to cleave thymine dimer

56 56

57 Excision repair Nonspecific repair Damaged region is removed and replaced by DNA synthesis 3 steps 1.Recognition of damage 2.Removal of the damaged region 3.Resynthesis using the information on the undamaged strand as a template 57

58 58


Download ppt "Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CHAPTER 14 LECTURE SLIDES To run the animations you must be."

Similar presentations


Ads by Google