DNA Mutations.txt

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DNA Mutations.txt
2012-04-28 13:24:57
DNA mutations general

Lect 3 dna mutations
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  1. Types of DNA mutations (classification)
    • Dominant: Effect seen whether individual homo or heterozygous for mutation.
    • Recessive: Effect ONLY seen when individual is homozygous for mutation.
  2. How mutations classified?
    • According to:
    • 1. phenotypic effect
    • 2. spontaneous (result of natural chem. Process) or induced (thru exposure to chemicals or energy sources that damage nucleotides of DNA)
    • 3. location of mutation
    • 4. Type of molecular change induced
  3. Classifications based on location:
    • 1. Germline :Aka gametic, mutations occur in cells that GIVE RISE to GAMETES, while not usually affecting individual who is passing these on
    • 2. Somatic: Mutations occur in ANY somatic cells(every cell EXCEPT germline), so not passed on
    • 3. X or Y linked: Mutations affect a gene on one of the SEX chromosomes
    • 4. Autosomal: mutations affect gene on ANY of autosomes
  4. Amorph:
    • LOSS of gene function
    • Usually RECESSIVE
    • Blocks Transcription and Translation
  5. Hypomorph:
    • PARTIAL LOSS of function
    • Usually RECESSIVE
    • Leads to REDUCED gene/protein expression or protein activity
  6. Hypermorph:
    • PARTIAL GAIN of function
    • Usually DOMINANT
    • Leads to INCREASED gene/protein expression or protein activity
  7. Antimorph:
    • Dominant Negative – acts to compete with and OPPOSE normal gene activity
    • Usually DOMINANT
    • Leads to ALTERED gene/protein expression that COMPETES with normal
  8. Neomorph:
    • New Function
    • Usually DOMINANT
    • Leads to ALTERED gene/protein expression (expression in novel tissue) or a NEW protein FXN
  9. Frameshift:
    SHIFTS reading frame, causing a shift in all sequences and therefore affects all amino acid sequences, most likely causes lack of gene function
  10. Missense:
    Changes ONE nucleotide (point mutation), swapping one for another, possibly changing the amino acid, but nothing downstream, not as drastic affect as frameshift
  11. Causes of Mutation
    • 1. Replication errors
    • 2. tautomeric shifts
    • 3. base analogs
    • 4. alkylating agents
    • 5. Intercalating agents
    • 6. deamination
    • 7. depurination
    • 8. UV
  12. Tautomeric shifts:
    • Change CONFORMATION of nitrogenous base due to PROTEIN shift
    • Ie: Thymine can switch from Keto to >> Enol form (2>>>3 hydrogen bonds)
  13. Base analogs:
    • Molecules that can substitute for purines or pyrimidines during nucleotide synthesis, but PAIR DIFFERENTLY
    • Ie: Thymine analog can pair with Guanine (analog has 3Hbonds to pair better w/G)
  14. Alkylating agents:
    CHEMICALS which donate alkyl (methyl or ethyl) groups to THYMINE or GUANINE
  15. Intercalating agents:
    Molecules that Intercalate B/W BPs in DNA helix, causing distortions, that may lead to deletion or add’n of bps when repaired.
  16. Deamination:
    • Exchange of AMINO group (NH2) for a KETO group (double bonded O)
    • Ie: Cytosine to >>> Uracil
    • Also Oxidative Deamination: adenine or cytosine to >>> hypoxanthine
  17. Depurination:
    • REMOVAL of purine base from sugar phosphate backbone
    • Repair may result in inserting wrong base …mutations
  18. UV:
    • UV Light: Cause Pyrimidine dimers (ie w/adjacent thymidines), NOT reverse, deletions or insertions during repair
    • Ionizing Radiation: BREAKS sugar phosphate backbone, Causes Deletions, inversions and translocations