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microbio > lecture 7, chapter 8 > Flashcards

lecture 7, chapter 8 Flashcards

1
Q

through ______, organisms adapt to ever-changing environments

A

natural selection

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2
Q

what are the two general mechanisms that bacteria use to adjust to new circumstances?

A

regulation of gene expression, genetic change

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3
Q

what is often used as a model system of genetic change?

A

E. coli

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4
Q

why is E.coli a good model system of genetic change?

A

it’s easy to grow, inexpensive, rapid accumulation of large numbers

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5
Q

what are the two mechanisms of genetic change in bacteria?

A

mutation and horizontal gene transfer

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6
Q

what is mutation?

A

changes in existing nucleotide sequence

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7
Q

what is horizontal gene transfer?

A

movement of DNA from one organism to another

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8
Q

changes are passed to progeny by _________

A

vertical gene transfer

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9
Q

changes in organism’s DNA alters _________

A

genotype

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10
Q

changes in genotype often changes ______

A

phenotype

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11
Q

phenotype is also known as

A

observable characteristics

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12
Q

phenotype is also influenced by _______

A

environmental conditions

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13
Q

genotype is ______

A

sequence of nucleotides in DNA

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14
Q

the bacteria of a genotype are _____, meaning ______

A

haploid, there is only one copy with no backup

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15
Q

what does the deletion of gene for tryptophan biosynthesis yield?

A

a mutant that only grows if tryptophan is supplied

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16
Q

if growth factor is required, mutant is termed ______

A

auxotroph

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17
Q

auxo means _____

A

increase

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18
Q

troph means _____

A

nourishment

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19
Q

proto means _____

A

first

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20
Q

_______ does not require growth factors

A

prototroph

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21
Q

geneticists compare mutants to _____

A

wild type

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22
Q

wild-type E.coli strain is ______

A

prototroph

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23
Q

what are strains designated by?

A

three-letter abbreviations

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24
Q

three-letter abbreviation for streptomycin resistance

A

Str^R

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25
Q

three-letter abbreviation meaning “cannot make tryptophan”

A

Trp^-

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26
Q

genetic changes that result from normal processes

A

spontaneous mutations

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27
Q

spontaneous mutations occur ______

A

randomly at infrequent, but characteristic rates

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28
Q

probability of mutation per cell division

A

mutation rate

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29
Q

what is the mutation rate typically between for a given gene?

A

10^-4 to 10^-12

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30
Q

what are mutations passed to?

A

progeny

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31
Q

mutations are most frequently the result of ______

A

unrepaired replication errors

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32
Q

what is it called when a mutation occasionally changes back to it’s original state?

A

reversion

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33
Q

when does reversion occur?

A

spontaneously at low frequencies

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34
Q

_______ does not cause mutations, but selects cells that grow under its conditions

A

environment

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35
Q

large populations such as cells in a colony contain _____; not all cells are identical

A

mutants

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36
Q

what is more likely, a single mutation or a two mutations at the same time?

A

a single mutation.
single mutations are rare enough, but two mutations at the same time are even more unlikely

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37
Q

why might physicians give two antimicrobial medications simultaneously?

A

to reduce resistance

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38
Q

an organisms that has mutated to become resistant to an antimicrobial medication will _______

A

become dominant in an environment where the medication is present

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39
Q

chance that a cell will become resistant to both antimicrobial medications is ________

A

the product of mutation rate for each gene

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40
Q

what is the most common spontaneous mutation?

A

base substitution

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41
Q

______ is change of a single base pair

A

point mutation

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42
Q

what is the following mutation? incorrect nucleotide incorporated during DNA synthesis

A

base substitution

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43
Q

what are the three possible outcomes of base substitution?

A

silent (synonymous) mutation, missense mutation, nonsense mutation

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44
Q

silent (synonymous) mutation introduces _______

A

wild-type amino acid

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45
Q

missense mutation introduces ________

A

a different amino acid

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46
Q

does the resulting protein of a missense mutation function normally?

A

No

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47
Q

nonsense mutation specifies _____

A

stop codon

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48
Q

what does a nonsense mutation yield?

A

shorter, often non-functional protein

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49
Q

for deletion/addition of nucleotides, what does the impact depend on?

A

the number of nucleotides involved and location within protein

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50
Q

how many pairs changes one codon?

A

three

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51
Q

the deletion/addition of one or two pairs results in _____

A

frameshift mutation

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52
Q

what do frameshift mutations often result in?

A

premature stop codon; leading to shortened, nonfunctional protein

53
Q

in what mutation is a different set of codons translated?

A

frameshift mutation

54
Q

pieces of DNA that can move from one location to another in a cell’s genome; process of transposition

A

transposons (jumping genes)

55
Q

gene into which transposon jumps is inactivated; function disrupted

A

insertional inactivation

56
Q

most transposons have _____

A

transcriptional terminators

57
Q

what do transcriptional terminators in transposons block?

A

expression of downstream genes in operon

58
Q

induced mutations result from ______

A

outside influence

59
Q

any substance that increase the spontaneous mutation rate is a ______

A

mutagen

60
Q

what does a mutagen induce?

A

a mutation

61
Q

geneticists may use mutagens to ______

A

increase the mutation rate

62
Q

what are the two general types of mutagens?

A

chemical agent, radiation

63
Q

what are the three types of chemical mutagens?

A

chemicals that modify nucleobases, base analogs, intercalating agents

64
Q

what are the two types of radiation mutagens?

A

ultraviolet (UV) light, x-rays

65
Q

what is the action of chemicals that modify nucleobases?

A

chemical modification change base-pairing properties of nucleobases

66
Q

base-pairing properties differ from ______

A

those of nucleobases normally found in DNA

67
Q

where do intercalating agents insert?

A

between adjacent base pairs in a DNA strand, pushing them apart

68
Q

where do transposons insert?

A

randomly into DNA, into cell’s genome

69
Q

what does ultraviolet light cause?

A

thymine dimers to form

70
Q

what do x-rays cause?

A

single and double strand breaks in DNA

71
Q

what is the result of chemicals that modify nucleobases

A

nucleotide substitution

72
Q

what is the result of base analogs?

A

nucleotide subsitution

73
Q

what is the result of intercalating agents?

A

addition or subtraction of nucleotides

74
Q

what is the result of transposons?

A

insertional inactivation

75
Q

what is the result of ultraviolet light?

A

errors during repair process

76
Q

what is the result of x-rays?

A

deletions

77
Q

chemicals that modify nucleobases increase chance of _____

A

incorrect nucleotide incorporation

78
Q

alkylating agents add ______ onto nucleobases

A

alkyl groups

79
Q

_______ adds methyl group to guanine

A

nitrosoguanidine

80
Q

when a methyl group is added to guanine, the resulting methylguanine may base-pair with ______

A

thymine

81
Q

base analogs resemble

A

nucleobases

82
Q

why do base analogs differ from nucleobases?

A

they have different hydrogen-bonding properties

83
Q

base analogs can be incorporated into DNA by _______

A

DNA polymerase

84
Q

in base analogs, where is the wrong nucleotide incorporated into?

A

complementary strand during DNA replication

85
Q

what does 5-bromouracil resemble?

A

thymine

86
Q

what does 5-bromouracil often base-pair with?

A

guanine

87
Q

what does 2-amino purine resemble?

A

adenine

88
Q

what does 2-amino purine often pair with?

A

cytosine

89
Q

intercalating agents increase _______

A

frameshift mutations (leading to errors during replication)

90
Q

structure of intercalating agents

A

flat molecules

91
Q

what happens when an intercalating agent is in a template strand?

A

a base pair is added to synthesized strand

92
Q

what happens if an intercalating agent is in a strand being synthesized?

A

a base pair is deleted

93
Q

intercalating agents often result in _____

A

a premature stop codon

94
Q

what are thymine dimers

A

covalent bonds between adjacent thymines

95
Q

what can ultraviolet light cause?

A

distortion of molecule, replication and transcription stall

96
Q

mutations due to UV light results from _____

A

cell’s SOS repair mechanism

97
Q

double-strand breaks as a result of x rays can be ____

A

lethal

98
Q

what can x-rays alter?

A

nucleobases

99
Q

________ can be introduced intentionally to generate mutations

A

transposons

100
Q

_______ generally inactivates gene into which it inserts

A

transposon

101
Q

what happens if damaged DNA is not repaired?

A

cell death; cancer in animals

102
Q

why are mutations rare?

A

because alterations in DNA generally repaired before being passed to progeny

103
Q

in humans, two genes associated with breast cancer code for DNA repair enzymes. what is the result of mutations in either gene?

A

high probability of breast cancer

104
Q

during replication, _______ sometimes incorporates the wrong nucleotide

A

DNA polymerase

105
Q

mutations is prevented by _____

A

repairing before DNA replication

106
Q

what are the two mechanisms of repair?

A

proofreading and mismatch repair

107
Q

what is proofreading done by?

A

DNA polymerase

108
Q

what can DNA polymerase do during proofreading?

A

checks accuracy, can back up and remove incorrect nucleotide, inserts correct nucleotide

109
Q

is DNA polymerase perfect at proofreading?

A

no, but it is very efficient

110
Q

what fixes errors missed by DNA polymerase?

A

mismatch repair

111
Q

steps of mismatch repair

A

1) enzyme cuts sugar-phosphate backbone of new DNA strand
2) another enzyme degrades short region of DNA strand with error
3) DNA polymerase, DNA ligase fill in and seal the gap

112
Q

_______ of DNA indicates template strand

A

methylation

113
Q

newly synthesized strand is ______

A

unmethylated

114
Q

modified nucleobases lead to _____

A

base substitutions

115
Q

steps of modified nucleobase repair

A

1) glycosylase removes oxidized nucleobase
2) another enzyme cuts DNA at this site
3) DNA polymerase removes short section; synthesizes replacement
4) DNA ligase seals gap

116
Q

what is photoreactivation?

A

light repair

117
Q

photoreactivation is only found in _____

A

bacteria

118
Q

in photoreactivation, ____ uses energy from light

A

enzyme

119
Q

what does photoreactivation break?

A

covalent bonds of thymine dimer

120
Q

what is excision repair?

A

dark repair

121
Q

in excision repair, _____ removes damage

A

enzyme

122
Q

in excision repair, after the enzyme removes damage, what occurs?

A

DNA polymerase, DNA ligase fill in and seal the gap

123
Q

last-ditch repair mechanisms used when other systems fail

A

SOS repair

124
Q

when is SOS repair induced?

A

following extensive DNA damage that stalls DNA and RNA polymerases

125
Q

how many genes are in SOS system?

A

several dozen

126
Q

SOS system includes a _______ that synthesizes even in extensively damaged regions

A

DNA polymerase

127
Q

why are errors made in SOS system?

A

because the DNA polymerase in the SOS system has no proofreading ability

128
Q

errors made during SOS repair results in _____

A

SOS mutagenesis

129
Q
A

microbio (8 decks)

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