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microbio > lecture 8, chapter 8 > Flashcards

lecture 8, chapter 8 Flashcards

1
Q

cells inoculated onto medium that supports growth of mutant but not parent

A

direct selection

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2
Q

________ grow on medium with the antibiotic, but parents do not

A

antibiotic-resistant mutants

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3
Q

________ isolates auxotroph from prototrophic parent strain

A

indirect selection

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4
Q

why is indirect selection more difficult?

A

since parents grow on any media on which auxotroph can grow

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5
Q

_______ indirectly selects auxotrophs

A

replica plating

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6
Q

steps of replica plating

A

1) master plate with nutrient agar pressed onto velvet
2) velvet with adhering cells pressed onto sterile media in consistent orientation
3) colonies that are missing on glucose-salts agar allow identification of auxotrophs on master plate

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7
Q

all cells will form colonies on ______

A

nutrient agar

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8
Q

_______ fail to grow in glucose-salts agar

A

auxotrophs

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9
Q

__________ selectively kills prototrophs

A

penicillin enrichment

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10
Q

penicillin increase _______ before replica plating

A

auxotrophs

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11
Q

what type of cell does penicillin kill?

A

only growing cells

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12
Q

_______ grow in glucose-salts medium

A

prototrophs

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13
Q

________ added before cells are plated on nutrient agar to create master plate

A

penicillinase

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14
Q

_______ cause many cancers; most are mutagens

A

carcinogens

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15
Q

what do mutagens increase?

A

low frequency of spontaneous reversions

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16
Q

animal tests are expensive and time-consuming. it is quicker and cheaper to test ________ of chemicals in microbiological systems (screening for carcinogens)

A

mutagenic effect

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17
Q

what measures the effect of chemicals on reversion rate of histidine-requiring Salmonella auxotroph?

A

Ames test

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18
Q

ames test uses ______

A

direct selection on glucose-salts plate

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19
Q

only prototrophs that have undergone revision can grow on ______

A

glucose-salts plate

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20
Q

what happens if a chemical is mutagenic?

A

reversion rate increases relative to control (more colonies grow)

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21
Q

why is rat liver extract sometimes added to an ames test?

A

because non-carcinogenic chemicals may be converted to carcinogens by animal enzymes

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22
Q

additional tests are done on mutagenic chemicals to determine if they are _____

A

also carcinogenic

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23
Q

_______ acquire genes from other cells by horizontal gene transfer

A

recombinants

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24
Q

recombinants can demonstrate with ______

A

auxotrophs

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25
Q

if colonies grow on glucose-salts medium during horizontal gene transfer, what does it mean?

A

these colonies most likely acquired genes from another strain

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26
Q

recombinants combine two strains that ________

A

cannot grow on glucose-salts medium

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27
Q

for recombinants, ______ are unlikely; simultaneous mutations required

A

spontaneous mutants

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28
Q

what are the three mechanisms in which genes are naturally transferred during horizontal gene transfer?

A

DNA-mediated transformation, transduction, conjugation

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29
Q

“naked” DNA taken up from the environment

A

DNA-mediated transformation

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30
Q

bacterial DNA transfer by a virus

A

transduction

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31
Q

DNA transfer during cell-to-cell contact (between bacterial cells)

A

conjugation

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32
Q

transferred DNA is replicated only if there is a ______ with origin of replication

A

replicon

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33
Q

examples of replicons

A

chromosomes, plasmids

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34
Q

DNA fragments can be added to recipient chromosome by ________

A

homologous recombination

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35
Q

what happens in homologous recombination?

A

donor DNA replaces complementary region of recipient cell’s DNA

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36
Q

DNA-mediated transformation involves ______

A

uptake of naked DNA

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37
Q

what is naked DNA?

A

DNA not within a cell or virus

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38
Q

where does naked DNA originate from?

A

cells that have burst or secreted it

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39
Q

addition of ______ prevents DNA-mediated transformation

A

DNase

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40
Q

recipient cell in DNA-mediated transformation must be ______

A

competent

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41
Q

what type of DNA do most recipient cells take up?

A

DNA regardless of origin

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42
Q

some recipient cells only accept DNA from _____

A

closely related bacteria

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43
Q

some recipient cells are always competent, while others ________

A

become competent under certain conditions

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44
Q

steps of DNA-mediated transformation

A

1) single strand of DNA binds to cell surface and enters cell
2) new DNA integrates into chromosome by homologous recombination
3) one daughter cell will inherit donor DNA
4) transformed cells can be detected by growing on medium that will not allow growth of non-transformed cells

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45
Q

streptococcus pneumoniae is only pathogenic when it is ______

A

encapsulated

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46
Q

how were living non-encapsulated cells transformed by DNA?

A

from heat-killed encapsulated cells and produced living encapsulated cells

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47
Q

transfer of bacterial genes by bacteriophages

A

transduction

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48
Q

bacteriophages are also termed ____

A

phages

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49
Q

what infects bacterial cells in transduction?

A

phages

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50
Q

how do phages infect bacterial cells?

A

1) they attach to cell and inject nucleic acid
2) then the phage enzymes cut bacterial DNA into small pieces.
3) bacterial cell enzymes produce phage nucleic acid and a phage coat
4) then phage particles are released from bacterial cell

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51
Q

what are components of new phage bacterial cells?

A

phage nucleic acid and a phage coat produced by bacterial cell enzymes

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52
Q

________ results when a fragment of bacterial DNA enters the phage protein coat

A

generalized transduction

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53
Q

what does generalized transduction produce?

A

a transducing particle

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54
Q

what happens when a transducing particle attaches to another bacterial cell?

A

it injects the DNA it contains into the bacterial cell

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55
Q

when a transducing particle injects DNA into another bacterial cell, what occurs?

A

the new DNA may be integrated into chromosome

56
Q

what does conjugation require?

A

contact between donor and recipient cells

57
Q

_______ direct their own transfer during conjugation

A

conjugative plasmids

58
Q

_____ do not have to integrate into chromosomes during conjugation

A

replicons

59
Q

F plasmid is also known as _____

A

fertility

60
Q

the F plasmid of _____ is the most studied

A

E. coli

61
Q

____ contain F plasmid, ____ do not

A

F+, F-

62
Q

what does F plasmid encode?

A

F pilus (sex pilus)

63
Q

what do other plasmids encode?

A

resistance to some antibiotics

64
Q

resistance to antibiotics is easy/difficult to spread (choose one)

A

easy

65
Q

steps of plasmid transfer

A

1) f pilus binds to receptor on recipient cell wall
2) f pilus contracts, pulling cells together
3) enzyme cuts plasmid at origin of transfer
4) single DNA strand is transferred
5) complementary strands synthesized
6) both cells are now F+

66
Q

what does chromosome transfer involve?

A

Hfr cells (high frequency of recombination)

67
Q

F plasmid is integrated into chromosome via ___________

A

homologous recombination

68
Q

chromosome transfer is reversible/irreversible (choose one)

A

reversible

69
Q

when does F’ plasmid result?

A

when a small piece of chromosome is removed with F plasmid DNA

70
Q

F’ plasmid is _____; transferred to F- cells

A

replicon

71
Q

what does F’ plasmid carry?

A

bacterial DNA into new cells

72
Q

what does Hfr cell produce?

A

F pilus

73
Q

where does integrated F plasmid begin transfer of genes?

A

on one side of the origin of transfer of plasmid

74
Q

All of/part of chromosome is transferred to recipient cell (choose one)

A

part of

75
Q

chromosome usually _____ before complete transfer

A

breaks

76
Q

recipient cell of chromosome transfer remains _____

A

F-, since incomplete F plasmid was transferred

77
Q

there is a lot of ______ in gene pool of a single species

A

variation

78
Q

less than ____ of E.coli genes found in all strains

A

50%

79
Q

what is the core genome of a species?

A

the amount of genes of a particular species found in all strains of that species

80
Q

the remaining parts of the core genome are termed _____

A

the mobile gene pool

81
Q

the mobile gene pool can move from ____

A

one DNA molecule to another

82
Q

examples of mobile gene pool/mobile genetic elements

A

plasmids, transposons, genomic islands, phage DNA

83
Q

replicon that is independent of the chromosome and generally encodes only non-essential genetic information

A

plasmid

84
Q

segment of DNA that directs its own movement to another location in chromosomal or plasmid DNA

A

transposon

85
Q

large genomic segment in a cell’s genome that originated in another species

A

genomic island

86
Q

phage genome that sometimes carries additional genes

A

phage DNA

87
Q

_______ common in microbial world

A

plasmids

88
Q

plasmids are usually ____ with origin of replication

A

dsDNA

89
Q

_______ generally encode nonessential information, but may allow survival in particular environment

A

plasmids

90
Q

plasmids have _________ genes

A

few to many

91
Q

low-copy-number

A

one or a few per cell

92
Q

high-copy-number

A

many, up to 500

93
Q

plasmids can have ______ to _______

A

low copy number to high copy number

94
Q

most plasmids have ________; some replicate in many different species

A

narrow host range

95
Q

plasmids in same compatibility group can/cannot be maintained in the same cell (choose one)

A

cannot

96
Q

_______ requires conjugative plasmid for transfer

A

mobilizable plasmid

97
Q

organisms in which antibiotic resistance is found

A

many

98
Q

organisms in which antibiotic synthesis is found

A

streptomyces species

99
Q

organisms in which gas vacuole production is found

A

halobacterium species

100
Q

organisms in which increased virulence is found

A

yersinia and shigella species

101
Q

organisms in which insect toxin synthesis is found

A

bacillus thuringiensis

102
Q

organisms in which nitrogen fixation is found

A

rhizobium species

103
Q

organisms in which oil degradation is found

A

psuedomonas species

104
Q

organisms in which pilus synthesis is found

A

e.coli, pseudomonas species

105
Q

organisms in which toxin production is found

A

bacillus anthracis

106
Q

organisms in which tumor formation in plants

A

agrobacterium species

107
Q

what can bacteria conjugate with?

A

plants

108
Q

what causes crown gall?

A

agrobacterium tumefaciens

109
Q

what happens with crown gall?

A

cells multiply without hormones and produce opine

110
Q

tumor-inducing (Ti) plasmid is called

A

T-DNA (transferred DNA)

111
Q

where is T-DNA incorporated?

A

plant chromosome

112
Q

tumor formation genes can be replaced with _________ and incorporated into plant genome

A

beneficial genes

113
Q

what are R plasmids?

A

resistance plasmids

114
Q

what do resistance plasmids do?

A

encode resistance to antimicrobial medications

115
Q

many resistance plasmids are ______

A

conjugative plasmids with broad host range

116
Q

resistance plasmids can spread their resistance to ______ quickly

A

medications

117
Q

normal microbiota with R plasmids may transfer them to _______

A

pathogens

118
Q

what do transposons provide mechanism for?

A

moving DNA

119
Q

where can transposons move into?

A

other replicons in the same cell

120
Q

simplest transposon mechanism is ______

A

insertion sequence (IS)

121
Q

what does the insertion sequence do?

A

encodes only transposase enzyme, inverted repeats

122
Q

what type of transposon includes one or more genes?

A

composite transposons

123
Q

composite transposons integrate via __________

A

non-homologous recombination

124
Q

specific case: transposons yielded vancomycin-resistant Staphylococcus aureus strain. list the steps of how this occurred

A

1) patient infected with S. aureus that was susceptible to vancomycin
2) normal microbiota included vancomycin-resistant strain of Enterococcus faecalis
3) resistance encoded in transposon of plasmid transferred to S. aureus
4) transposon jumped to plasmid in S. aureus

125
Q

list the characteristics encoded by genomic islands

A

use of specific energy sources, acid tolerance, ability to cause disease

126
Q

nucleotide composition of genomic islands are very different from genome. what is the base pair ratio characteristic for each species?

A

G-C base pair ratio

127
Q

what are pathogenicity islands?

A

a distinct class of genomic islands acquired by microorganisms through horizontal gene transfer

128
Q

_________ degrade foreign DNA

A

restriction-modification systems

129
Q

what cuts DNA at a specific sequence in a restriction-modification system?

A

restriction enzyme

130
Q

how do modification enzymes protect the cell’s own DNA?

A

by adding methyl groups

131
Q

include small segments of phage DNA that recognize the specific DNA if it invades the cell again

A

CRISPR systems

132
Q

what is the first invasion of a CRISPR system?

A

complex of Cas proteins cuts DNA into short fragments

133
Q

what happens to the short fragments of DNA after the first invasion of a CRISPR system?

A

the fragments are inserted into chromosome at CRISPR array

134
Q

what is an integrated DNA fragment called?

A

a spacer

135
Q

_______ is transcription of CRISPR array that generates crRNAs that direct DNA-cutting enzymes to invading DNA

A

subsequent invasion

136
Q

what does CRISPR stand for?

A

clustered regularly short palindromic repeats

137
Q

what are CRISPR derived from?

A

bacteriophage that have previously infected the cell (are used to detect and destroy DNA from bacteriophages during subsequent infections)

microbio (8 decks)

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