Bmsc210 Mid2 p3

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Scottygo
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Bmsc210 Mid2 p3
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2013-03-08 17:28:10
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Bmsc210 Mid2 p3
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  1. Mutation
    – Heritable change in DNA sequence that can lead to a change in phenotype (observableproperties of an organism)
  2. Mutant
    – A strain of any cell or virus differing fromparental strain in genotype (nucleotidesequence of genome)
  3. Wild-type strain
    – Typically refers to strain isolated from nature
  4. Selectable mutations (Figure 10.1)
    • – Those that give the mutant a growth advantage under certain conditions
    • – Useful in genetic research
  5. Nonselectable mutations
    • – Those that give the mutant neither an advantagen or a disadvantage over the parent, or cause a disadvantage, e.g. inability to grow under certain conditions
    • – Detection of such mutations requires examininga large number of colonies and looking fordifferences (screening)
  6. Screening is always ____ tedious than selection.(more or less)
    more
  7. Replica plating
    • -useful for identification of cells with a nutritional requirement for growth(auxotroph)
    • -Method to facilitate screening
  8. Induced mutations
    •  – Those made environmentally or deliberately
    • – Can result from exposure to natural radiation oroxygen radicals
  9. Spontaneous mutations
    – Those that occur without external intervention
  10. Point mutations (Figure 10.3)
    • – Mutations that change only one base pair
    • – Can lead to single amino acid change in a protein, an incomplete protein, or no change at all
  11. Silent mutation
     – Does not affect amino acid sequence
  12. Missense mutation
    – Amino acid changed; polypeptide altered
  13. Nonsense mutation
    – Codon becomes stop codon; polypeptide is incomplete
  14. 􀅖 Frameshift mutations (Figure 10.4)
    • – Deletions or insertions that result in a shift inthe reading frame
    • – Often result in complete loss of gene function
  15. Point mutations are typically irreversable/reversible
    reversible
  16. Reversion
    – Alteration in DNA that reverses the effects ofa prior mutation
  17. Revertant
    (def)
    (2 types)
    • – Strain in which original phenotype is restored– Two types
    • • Same-site revertant: mutation is at the same site as original mutation
    • • Second-site revertant: mutation is at a different site in the DNA
  18. suppressor
    • mutation that compensates for the effect of the original mutation
    • -second site revertant
  19. For most microorganisms, errors in DNA replication occur at a frequency of ___to___  per kilobase
    10-6 to 10-7
  20. DNA viruses have error rates ___to___ times greater
    100–1000x
  21. The mutation rate in RNA genomes is ____fold higher than in DNA genomes
    • 1000
    • – Some RNA polymerases have proofreading capabilities
    • – However, RNA repair mechanisms similar to DNA repair mechanisms do not exist
  22. Mutagens:
    • chemical, physical, or biological agents that increase mutation rates
    • -chemical modifications
    • -frameshift mutations ex: acridines(an intercalating agent)
  23. Two main categories of mutagenic electromagnetic radiation
    • – Non-ionizing (i.e., UV radiation)
    • • Purines and pyrimidines strongly absorb UV
    • • Pyrimidine dimer is one effect of UV radiation
    • – Ionizing (i.e., X-rays, cosmic rays, and gammarays)
    • • Ionize water and produce free radicals
    • • Free radicals damage macromolecules in the cell
  24. Three Types of DNA Repair Systems
    • – Direct reversal
    • – Repair of single strand damage
    • – Repair of double strand damage
  25. Direct reversal:
    mutated base is stillrecognizable and can be repaired withoutreferring to other strand
  26. Repair of single strand damage:
    damaged DNA is removed and repaired using opposite strand as template
  27. – Repair of double strand damage: a break inthe DNA
    • Requires more error-prone repair mechanisms
  28. When DNA damage is large scale, the cell may use a different type of repair system (i.e., damage interferes with DNA replication)
    (2 types)
    • – Mechanism called the SOS regulatory system (Figure 10.7)
    • • This system is more error prone
    • • Allows replication to proceed and cell to replicate, but errors are more likely
    • – Translesion synthesis allows DNA to be synthesized with no template
  29. Perfect fidelity in organisms is ____ because it _____ evolution
    • counterproductive
    • prevents
  30. The mutation rate of an organism is/isnt subject to change
    • is
    • – Mutants can be isolated that are hyperaccurate or have increased mutation rates
  31. The Ames Test
    • 􀅖 The Ames test makes practical use of bacterial mutations to detect for potentially hazardous chemicals (Figure 10.8)
    • – Looks for an increase in mutation of bacteria in the presence of suspected mutagen
    • – A wide variety of chemicals have been screened for toxicity and carcinogenicity

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