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8.5 DNA Repair

8.5 DNA Repair. At the end of S phase, DNA polymerase has copied both strands of template DNA DNA polymerase does make mistakes -1 mistake every 10,000 bases. What is a mutation?. Mutation any change in DNA sequence Results vary Silent (very minor) Harmful (major) Lethal (death)

ivy-cervantes
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8.5 DNA Repair

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  1. 8.5 DNA Repair At the end of S phase, DNA polymerase has copied both strands of template DNA DNA polymerase does make mistakes -1 mistake every 10,000 bases

  2. What is a mutation? • Mutation • any change in DNA sequence • Results vary • Silent (very minor) • Harmful (major) • Lethal (death) • These mutations will be passed on to next generation of cells

  3. DNA Repair Mechanisms • Body must fix errors(mutations) in DNA • Two types • 1. DNA polymerases proofreading • Most common way of repair • 2. Excision Repair

  4. Polymerase Proofreading • DNA polymerase makes a mistake every 10,000 bases • As DNA polymerase adds nucleotide, it proofreads • Will remove wrong nucleotide • Add correct nucleotide After it is done, only 1 error every 10 million bases

  5. 2nd method: Excision Repair • Other mutations arise • Not during DNA replication • Other times during cell life • Caused by outside Mutagenic factors • Chemical • radiation

  6. Chemical Mutagenic Factors • Anything that causes a mutation, a change or error in DNA sequence • 1. Chemical Factors • Chemical molecules physically bind to DNA • Ex. Benzopyrene • Hetrocyclic amines • pesticides 2. Radiation • Physically damages DNA

  7. Radiation Mutagenic Factors • Anything that causes a mutation, a change or error in DNA sequence 2. Radiation: Physically damages DNA • Ionizing Radiation • X-rays • Actually punch holes through DNA • UV Radiation • Sunlight • Causes kink between two thymines

  8. UV Radiation Damage to DNA • Causes portions of DNA to be bound together N T T N N A A N

  9. UV Radiation Damage to DNA • Creates “Thymine Dimers” • Does sunblock prevent mutations? N T T N N A A N

  10. Excision Repair • The mutations must be detected and corrected

  11. Excision Repair • Most common mutations are mismatches(wrong bases paired up) • Or a chemical molecule binds DNA

  12. Excision Repair • Special enzymes constantly circulate • Travel up and down DNA til they find “damaged DNA” • Mismatched bases don’t bond well- • form hump

  13. Excision Repair • 2nd step: Incision • Enzyme breaks sugar-phosphate bonds between damaged DNA and normal DNA • 3rd step: Excision • Damaged DNA region is removed

  14. Excision Repair • 4th step: Re-synthesis • DNA polymerase fills in deleted region • Last step: • “Ligase” forms bonds between new region and rest of DNA strand

  15. DNA Repair • What would happen if your body couldn’t repair mutations as efficiently? • What if you couldn’t fix UV damage? • Anyone ever watch “The Others?” http://www.wwlp.com/news/segments/sybersy/others.jpg

  16. Xeroderma Pigmentosa • Autosomal recessive disease(very rare) • Mutation in DNA repair protein • Protein responsible for replacing nucleotides in DNA of skin damaged by UV radiation Cells expose to sunlight have damage to DNA Now they can’t fix it

  17. Xeroderma Pigmentosa • Cannot be exposed to sunlight • Not even strong fluorescent light • Must stay indoors with windows covered to block out light. • Only a few seconds of exposure • Cause 3rd degree burns • Skin cancer

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