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25 Cards in this Set
- Front
- Back
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Survival of a cell depends on ?
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genetic stability
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Genetic stability requires?
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accurate mechanism for replication
repair of accidental lesions |
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Transitions
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substitution of a pyrimidine with another pyrimidine or a purine with another purine
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Transversions
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substitution of a pyrimidine with a purine or vice versa
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Frameshifts
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due to addition/deletion of bases
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What happens when replication errors are missed by proofreading activity?
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distortion in the DNA helix is recognized by strand directed mismatch repair
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How does E.coli recognize a mismatched base pair?
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both strands are methylated at A in the sequence GATC seq
there's a lag in the methylation of GATC seq in the newly synths strand the mechanism recognizes the lack of methyl b/c of the lag |
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How do eukary recognize mismatched base pairs?
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single stranded breaks or nicks provide the repair signal
MutL scans the DNA for a nick MutS recognizes mismatched bases |
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FAP
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familial adenomatous polyposis
colon cancer - phenotype is distinguished by the presence of polyps in the colon |
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HNPCC
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hereditary non-polyposis colon cancer
inherited mutation in one copy of mismatch repair gene (MMR) mutations in homologs of MutS and MutL are involved |
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Changes in DNA may occur do to?
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cellular metabolic activity
heat extreme pH radiations substances in environment |
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Spontaneous changes in DNA are?
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depurination
deamination |
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UV damage in DNA leads to?
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pyrimidine dimers
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Depurination
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removes a purine from the nucleotide
leads to deletion |
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Deamination
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converts C to U
removes amines from bases thymine has no amine - no deamination occurs |
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Base excision repair pathway
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U is an unusual base for DNA...
it is recognized and cleaved by uracil glycosylase... AP endonuclease and phosphodiesterase remove sugar phosphate... DNA poly adds new nucleot, ligase seals nick |
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Nucleotide excision repair pathway
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nuclease makes a cut on either side of the damage...
helicase removes the oligonucleotide... polymerase repairs and ligase seals the nick |
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RAD3 group
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yeast repair sensitivity to radiations
excision repair helicase required for repair, component of transcription factor associated with RNA polymerase |
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RAD6 group
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post replication repair
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RAD52 group
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recombination-mediated repair
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XP gene products
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in mammalian cells, required for thymine dimers, are part of transcription factor TFIIH
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Double strand breaks occur during:
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recombination (RAG proteins catalyzing recombination of immunoglobulins)
ionizing radiation, oxidizing agents |
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Double strand breaks are repaired by:
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homologous end-joining (HEJ)
non-homologous end joining (NHEJ) |
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NHEJ
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results in loss of original sequence
involves Ku70/Ku80 protein, DNA-PK, Artemis |
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HEJ
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restores the original sequence; no loss of sequence
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