mutation and repair

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mutation and repair
2011-09-14 18:37:11
biochemistry DNA mutation

MS1/Mod 2: Biochemistry; molecular basis of mutation
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  1. "window of opportunity"
    • few hrs after replication (if DNA pol repair mech fail) to repair the mismatch mut
    • due to A base in GATC sequences in DNA usually becoming methylated several hrs after replication...quindi DNA is momentarily hemimethylated (parental DNA is methylated and daughter strand is not...yet)
  2. mismatch repair
    • 1. finding mismatch: prot scan new DNA looking for mismatch bulges
    • 2. removal: methyl on parental DNA directs enz to remove DNA on strand w/ mismatch/non methyl
    • 3. repair: gap created; DNA pol makes new DNA segment and DNA ligase acts
  3. Xeroderma pigmentosum (XP)
    disease due to mut in genes encoding components of nuc excision repair pathway; thymine dimers not repair and DNA damage persists in replication resulting in mut

    mut DNA mediates carcinogenesis (act of oncogenes?)
  4. Hereditary, non-polyposis colon carcinoma (HNPCC)
    • (lynch syndrome); due to deficiency in hMSH2 and hMLH1 genes encoding proteins of methyl directed mismatch repair sys...unrepaired mut...lots cell growth
    • increased risk for cancer (esp colon)
  5. Fanconi's anemia
    Ataxia-telangiectasia and Bloom's syndrome
  6. Fanconi's anemia symptoms
    low WBC, RBC, platelets, increased genomic instability, increased risk of cancers, high prob of unprogrammed chrom translocations and recombinations
  7. Ataxia-telangiectasia
    defects in enz that normally repair dsDNA breaks (phosphodiester bonds)
  8. Bloom's syndrome
    defect in DNA ligase
  9. Fanconi's anemia treatment
    avoid ionizing radiation, administration w/ prot like erythropoietin (to stim blood cell counts), bone marrow transplant
  10. sub-types of human breast cancer
    mut in BRAC1 gene; prod of BRAC1 are assoc w/ prot that participate in homologous recombination repair sys that normally repairs dsDNA breaks
  11. types of BRAC1 gene mutations
    alt splice site, nonsense mut, frameshift mut
  12. beta thalassemia gene mutations
    promoter mut, splice site mut, polyA signal mut, non-sense, frameshift
  13. Burkitt's lymphoma mut
    abnormal translocation btw chrom 8 and chrom 14; c-myc gene expression no longer regulated and is stim to abnormally high degree
  14. Becker muscular dystrophies
    mut in 5'splice site of intron 19 of dystrophin gene, as a result dystrophin mRNA does not have exon 19; joining of exon 18 and exon 20 results in frameshift on transL of remaining of dystrophin mRNA
  15. splice site form of beat thalassaemia
    G to A substitution at pos 110 in intron 1 produces a new acceptor (AG) splice site; new site used 90% and normal site used 10%...quindi normal mRNA made 10% and severe thalassaemia; BUT BOTH normal and abnormal mRNA produced
  16. Myotonic dystrophy symptoms
    inherited; myotonia, cardiac arrhythmia, cataracts, male balding, male infertility, endocrinopathies
  17. myotonic dystrophy biochemistry
    • amplification of GCT (at 3' end outside coding region) in myotonin prot kinase gene
    • normal ppl-5-30 copies, abnormal ppl 50-100
  18. fragile X
    amplification of CGG in 5'UTR; mental retardation in male
  19. missense beta globin
    • occurs in AA 6
    • GAG (glu) to GTG (val)

    sickle cell
  20. nonsense beta globin
    stop codon after AA 7

    beta thalassaemia (anemia)
  21. frameshift beta globin
    deletion of T reside in Thr codon

    beta thalassaemia (anemia)
  22. trisomy 21 category frequencies
    • whole-chrom>partial
    • microtrisomies
    • triplication of single genes or functional DNA element
  23. DS symptoms
    mental retardation distinctive physical appearance, more likely to have acute megakaryocytic leukemia
  24. chrom 21 gene prod func
    DNA BP, TF, nuclear and PM prot, STP
  25. DS biochemistry
    coding and non-coding genes are over expressed; over expression of subunits of multimeric prot complexes (nucleosomes) lead to abnormal structure and function
  26. Burkitt's lymphoma
    due to unprogrammed site-specific chrom transL
  27. CML
    transL btw 9 and 22 which gives two new chrom; smr chrom is called Philadelphia
  28. Philadelphia chrom
    smr chrom in CML transL; encodes a fusion prot btw portions of bcr (breakpoint cluster region) and abl (gene coding for tyrosine kinase); stim cell division