Biochem 501: Part IV.4: Mutagenesis and Repair

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Biochem 501: Part IV.4: Mutagenesis and Repair
2013-12-06 01:06:53
Biochem 501 FINAL

Biochem 501 FINAL
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  1. Causes of DNA mutation (repair mechanism)
    • -Incorrect base incorporation (DNA Polymerase proofreading/mismatch repair)
    • -Chemical changes (i.e.)
    •    -Base alkylation (O6-methylguanine instead of adenosine)
    •    -Deamination (loss of exocyclic amino group, cytosine-->uracil)
    •    -Depurination (N-glycosidic bond between base/pentose cleaved)
    •    -Pyrimidine dimer (bond forms between adjacent T or C nucleotides)
  2. Mismatch repair relies on what?
    • Distinguishing template from new strand.
    • Repairs according to template
    • Relies on which is methylated, new strand won't be methylated for a few minutes
  3. Difference between DNA methylation and alklylation
    • Methylation: Added to distinguish template strands, not harmful, added to area that IS NOT the nucleotide base pairing
    • Alkylation: Can be addition of ethyl/methyl. Added to place that effects base pairing. HARMFUL
  4. Direct repair of alkylation:
    Demethylation by oxidative demethylation/methyltransferase
  5. Deamnation can turn what into what
    • Cytosine-->Uracil
    • Adenine-->Hypoxanthine
    • 5-methylcytosine-->Thymine
    • Guanine-->Xanthine
  6. Base deamination allows:
    Non-standard pairing
  7. Depurination
    • Only effect purines (A, G)
    • Cuts base off of pentose
    • Can cause mutations during replication
    •    -One side lacks a base, gets crimped and a missing base pair, phase shift
  8. Fixing Deamination or Depurination
    • Base excision repair:
    • Cuts out bad part, DNA polymerase goes and trys again.
  9. Pyrimidine dimerization
    • Only effects pyrimidines (CT)
    • Neighboring bases can bind each other
    • Repair mechanism: Nucleotide excision
  10. Repairing double strand breaks/SS breaks
    • Homologous recombinations/non-homologous end-joining
    • Base-excision
  11. Chromosomes are composed of
  12. Sister chromosomes have
    Homologous sequence
  13. Homologous recombination
    • -DS Break converted to DS gap with exonucleases
    • -Strands with 3' ends are degraded less
    • -Exposed 3' end pairs with intact homologue in sister chromatid
    • -3' end extends along the template of intact homologue until both ends are complete and a double crossover holliday intermediate is created.
    • -DNA is recreated on opposite side
    • Each newly finsihed side is snipped off and each sister is left with a section of the other
  14. A single holliday junction has how many potential cleavage planes?
    2, leading to two possible resolved forms.