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1: GENET 270 > Mutation > Flashcards

Mutation Flashcards

1
Q

mutant (def.)

A

an organism in which the base sequence of DNA has been changed

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2
Q

mutation (def.)

A

any heritable change in the DNA sequence

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3
Q

phenotype (def.)

A
  • observable properties of an organism
  • mutant vs. wildtype
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4
Q

genotype (def.)

A

actual sequence of the DNA of an organism

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5
Q

allele (def.)

A
  • different forms of the same gene
  • mutant vs. wildtype
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6
Q

Reversion (def.)

A

-a restoration of the original phenotype to a mutant
-due to restoration of the original sequence of the gene

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7
Q

Consequences of Mutation: - mutations that alter phenotype disrupt _____

A

protein function

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8
Q

Alteration of DNA/RNA/protein function - must disrupt DNA/RNA/protein sequence (ways):
1) _______
2) _________

A

-change sequence of one or more codons
-change reading frame (ORF = open reading frame)

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9
Q

silent MUTATIONS vs leaky mutations

A

silent: amino acid substitution that does not affect protein structure/activity
leaky: partial disruption in a protein’s activity

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10
Q

Conditional vs Non-conditional mutations

A

non- conditional: mutant phenotype expressed under all conditions
conditional: mutant phenotype only expressed under
certain conditions (ex. Temperature sensitive, Suppressor sensitive, Auxotrophic)

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11
Q

point mutation change? characteristics?

A

-alteration single base pair (transitions/reversions, single/double/triple), missense/nonsense
-can be leaky, revert

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12
Q

deletion mutation change? characteristics?

A

-removal of DNA
-not leaky, never revert

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13
Q

insertion mutation change? characteristics?

A

-addition new DNA
-not leaky, can revert

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14
Q

inversion mutation change? characteristics?

A

-inversion existing DNA
-not leaky, can revert

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15
Q

frameshift mutation change? characteristics?

A

-addition or deletion not equal to multiple of 3nt
-not leaky
-can revert

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16
Q

point mutation: transitions

A

Pu:Py pair -> Pu:Py pair
Py:Pu pair-> Py:Pu pair

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17
Q

point mutation: transversions

A

Pu:Py pair -> Py:Pu pair
Py:Pu pair -> Pu:Py pair

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18
Q

1952 Lederberg & Lederberg demonstrated direct evidence that phage T1r mutations occurred _________

A

spontaneously in E. coli before exposure to phage

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19
Q

1952 Lederberg & Lederberg lab technique

A

-used replica plating
- grew colonies on non-selective medium (no T1)
- replica plate to multiple plates spread with T1 phage
- T1r colonies appeared in same positions on each of replica plates

20
Q

mutation rates (def.)

A

probability that a gene will be mutated in a single generation- also referred to as chance of mutation to a particular phenotype

21
Q

mutations rate widely variable amongst different genes: dependent upon: _______ (3)

A
  • gene size
  • nucleotide sequence
  • number of genes that dictate phenotype
22
Q

Generation of Spont. mutations (3)

A

1) Replication errors
2) alteration of nucleotides
3) recombination

23
Q

2 types of replication errors

A

i) errors in nucleotide incorporation: incorporation of tautomeric bases during replications; causing transitions
ii) slipped strand mispairing (one strand of DNA slips during replication)

24
Q

Tautomer (def.)

A

alternative forms of bases with altered base-pairing properties

25
Q

adenine (imino form) bind ____; thymine (enol form) bind _____

A

-cytosine
-guanine

26
Q

tautomeric transitions may escape repair mechanisms because: ________ (2) p

A

1) proofreading -> tautomers are correctly hydrogen-bonded
2) mismatch repair -> tautomer may later assume normal structure, could be removed by the “mismatch repair”, but only if the tautomer is found in unmethylated daughter strand

27
Q

extra base is either added (slippage of ____ strand)
or deleted (slippage of _____ strand). slipping occurs in ______ sequences; causes _____ mutations

A

-daughter
-template
-short, repeated
-frameshift

28
Q

2 Alteration of Nucleotides

A

1) deamination: about 5% of cytosines in bacterial DNA are methylated (MeC); both MeC and C are deaminated occasionally
2) oxidation: reactive forms of oxygen from metabolism(peroxide/free radicals), react with and alter DNA bases (eg. guanine -> 8-oxo-guanine pairs with adenine instead of cytosine causing GC-> TA transversions)

29
Q

deamination C-> U

A

-U can pair with A
-GC -> AT transition
-repaired by uracil-N-glycosylase so that this rarely happens

30
Q

deamination MeC-> T

A

-T can pair with A
-GC -> AT transition
-MeC:G base pairs can be hotspots for mutation

31
Q

recombination between direct repeats leads to ____

A

deletions

32
Q

recombination between inverted repeats leads to ____

A

inversions

33
Q

mutagenesis -> treatments that alter the DNA; exposure of the whole organisms or just DNA to ______

A

-mutagens

34
Q

Base-Analog Mutagens: compound similar to ______ that can be incorporated into DNA during replication; H-bonds correctly, so escapes ____. to be mutagenic, must have _____
- eg. 5-bromouracil (BU); analog of _____ (tautomeric enol form predominant that frequently pairs with ___)
-causes _____ MUTATIONS
-if replaces a T in keto form, can tautomerize into enol form to yield _____
-can be misincorporated in enol form to yield ______
Base analog mutagens ALWAYS induce _____

A

-one of 4 DNA bases
-editing
- 2 modes of H-bonding
-thymine
-G
-TRANSITION
-AT -> GC
-GC -> AT
-transitions

35
Q

Chemical Mutagens -alter bases already incorporated into DNA to change _____

A

-H-bonding specificity

36
Q

types of chemical mutagens

A

1) nitrous acid (C-> U)
2) hydroxylamine
3) ethylmethane sulfonate (EMS)

37
Q

Intercalating Agents (def.)

A
  • planar, heterocyclic molecules with same dimensions as a Pu:Py base pair
38
Q

Intercalating Agents intercalates between _____ . During replication, _______ are inserted into DNA containing intercalating agents and generates _____ mutations. this may work by stabilizing looped out bases in _______

A
  • base pairs
    -extra base pairs
  • frameshift
  • slipped strand mispairing during replication
39
Q

mutagenesis by mutator genes: mutations in specific genes (_____) whose products are involved in _____; leads to _________ at other genes throughout the chr. (aka _____ phenotype)

A

-mut genes
-DNA repair
-a high mutation frequency
-mutator phenotype

40
Q

mutatator gene: mutD/dnaQ dam function

A

proofreading functionof DNA pol II; methylates DNA; directs mismatch repair to correct stand

41
Q

mutatator gene: mutH, mutL, mutS

A

mismatch repair

42
Q

isolation of mutations: screens

A
  • Mutants grow on media where phenotype of the mutants can be distinguished
    from parent
  • eg. COLOR INDICATOR PLATES
  • eg. identification of auxotrophic mutants based on inability to grow in the absence of certain metabolites (replica plating)
43
Q

isolation of mutations: selections

A
  • Mutants are identified based on their ability to grow under conditions that the
    parent cannot (Very Powerful)
  • can identify a mutant on single plate of 10^10 bacteria/phage
  • eg. resistance mutants (antibiotic, phage resistance)
  • consider a rare mutation (1/10^6)
44
Q

screens vs . selections

A

screen: 100 colonies/plaques per plate; must screen 10 000 plates
selections: 10^10 bacteria/phage; select mutant off 1 plate

45
Q

isolation of mutations: enrichments

A
  • procedures that enrich for mutant organisms
  • living, multiplying cells are killed by treatment, while non-growing
    mutant cells are not (eg. penicillin enrichment)
46
Q

isolation of mutations: Isolation of Conditionally Lethal Mutations

A

REPLICA PLATING
- mutants plated under permissive conditions –> selected under nonpermissive conditions (e.g. Host mutants)

1: GENET 270 (15 decks)

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