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

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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 3 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

4 4 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

5 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 5 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

6 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) 6

7 7 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

8 8 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

9 Double helix 2 strands are polymers of nucleotides Phosphodiester backbone – repeating sugar and phosphate units joined by phosphodiester bonds Wrap around 1 axis Antiparallel 9 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´

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11 Complementarity of bases A forms 2 hydrogen bonds with T G forms 3 hydrogen bonds with C Gives consistent diameter 11 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

12 12 DNA Replication Requires 3 things –Something to copy Parental DNA molecule –Something to do the copying Enzymes –Building blocks to make copy Nucleotide triphosphates

13 13 DNA replication includes –Initiation – replication begins –Elongation – new strands of DNA are synthesized by DNA polymerase –Termination – replication is terminated

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15 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 15 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

16 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 16 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Supercoiling Replisomes No Supercoiling Replisomes DNA gyrase

17 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 17

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19 19 Partial opening of helix forms replication fork DNA primase – RNA polymerase that makes RNA primer –RNA will be removed and replaced with DNA

20 Leading-strand synthesis –Single priming event –Strand extended by DNA pol III Processivity – subunit forms sliding clamp to keep it attached 20

21 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 21

22 22 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

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24 24 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

25 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 25

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27 27 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

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29 29 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

30 30 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

31 31 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

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33 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 33

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