lecture 8, chapter 8 Flashcards
(137 cards)
1
Q
cells inoculated onto medium that supports growth of mutant but not parent
A
direct selection
2
Q
________ grow on medium with the antibiotic, but parents do not
A
antibiotic-resistant mutants
3
Q
________ isolates auxotroph from prototrophic parent strain
A
indirect selection
4
Q
why is indirect selection more difficult?
A
since parents grow on any media on which auxotroph can grow
5
Q
_______ indirectly selects auxotrophs
A
replica plating
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
7
Q
all cells will form colonies on ______
A
nutrient agar
8
Q
_______ fail to grow in glucose-salts agar
A
auxotrophs
9
Q
__________ selectively kills prototrophs
A
penicillin enrichment
10
Q
penicillin increase _______ before replica plating
A
auxotrophs
11
Q
what type of cell does penicillin kill?
A
only growing cells
12
Q
_______ grow in glucose-salts medium
A
prototrophs
13
Q
________ added before cells are plated on nutrient agar to create master plate
A
penicillinase
14
Q
_______ cause many cancers; most are mutagens
A
carcinogens
15
Q
what do mutagens increase?
A
low frequency of spontaneous reversions
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
17
Q
what measures the effect of chemicals on reversion rate of histidine-requiring Salmonella auxotroph?
A
Ames test
18
Q
ames test uses ______
A
direct selection on glucose-salts plate
19
Q
only prototrophs that have undergone revision can grow on ______
A
glucose-salts plate
20
Q
what happens if a chemical is mutagenic?
A
reversion rate increases relative to control (more colonies grow)
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
22
Q
additional tests are done on mutagenic chemicals to determine if they are _____
A
also carcinogenic
23
Q
_______ acquire genes from other cells by horizontal gene transfer
A
recombinants
24
Q
recombinants can demonstrate with ______
A
auxotrophs
25
if colonies grow on glucose-salts medium during horizontal gene transfer, what does it mean?
these colonies most likely acquired genes from another strain
26
recombinants combine two strains that ________
cannot grow on glucose-salts medium
27
for recombinants, ______ are unlikely; simultaneous mutations required
spontaneous mutants
28
what are the three mechanisms in which genes are naturally transferred during horizontal gene transfer?
DNA-mediated transformation, transduction, conjugation
29
"naked" DNA taken up from the environment
DNA-mediated transformation
30
bacterial DNA transfer by a virus
transduction
31
DNA transfer during cell-to-cell contact (between bacterial cells)
conjugation
32
transferred DNA is replicated only if there is a ______ with origin of replication
replicon
33
examples of replicons
chromosomes, plasmids
34
DNA fragments can be added to recipient chromosome by ________
homologous recombination
35
what happens in homologous recombination?
donor DNA replaces complementary region of recipient cell's DNA
36
DNA-mediated transformation involves ______
uptake of naked DNA
37
what is naked DNA?
DNA not within a cell or virus
38
where does naked DNA originate from?
cells that have burst or secreted it
39
addition of ______ prevents DNA-mediated transformation
DNase
40
recipient cell in DNA-mediated transformation must be ______
competent
41
what type of DNA do most recipient cells take up?
DNA regardless of origin
42
some recipient cells only accept DNA from _____
closely related bacteria
43
some recipient cells are always competent, while others ________
become competent under certain conditions
44
steps of DNA-mediated transformation
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
45
streptococcus pneumoniae is only pathogenic when it is ______
encapsulated
46
how were living non-encapsulated cells transformed by DNA?
from heat-killed encapsulated cells and produced living encapsulated cells
47
transfer of bacterial genes by bacteriophages
transduction
48
bacteriophages are also termed ____
phages
49
what infects bacterial cells in transduction?
phages
50
how do phages infect bacterial cells?
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
51
what are components of new phage bacterial cells?
phage nucleic acid and a phage coat produced by bacterial cell enzymes
52
________ results when a fragment of bacterial DNA enters the phage protein coat
generalized transduction
53
what does generalized transduction produce?
a transducing particle
54
what happens when a transducing particle attaches to another bacterial cell?
it injects the DNA it contains into the bacterial cell
55
when a transducing particle injects DNA into another bacterial cell, what occurs?
the new DNA may be integrated into chromosome
56
what does conjugation require?
contact between donor and recipient cells
57
_______ direct their own transfer during conjugation
conjugative plasmids
58
_____ do not have to integrate into chromosomes during conjugation
replicons
59
F plasmid is also known as _____
fertility
60
the F plasmid of _____ is the most studied
E. coli
61
____ contain F plasmid, ____ do not
F+, F-
62
what does F plasmid encode?
F pilus (sex pilus)
63
what do other plasmids encode?
resistance to some antibiotics
64
resistance to antibiotics is easy/difficult to spread (choose one)
easy
65
steps of plasmid transfer
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
what does chromosome transfer involve?
Hfr cells (high frequency of recombination)
67
F plasmid is integrated into chromosome via ___________
homologous recombination
68
chromosome transfer is reversible/irreversible (choose one)
reversible
69
when does F' plasmid result?
when a small piece of chromosome is removed with F plasmid DNA
70
F' plasmid is _____; transferred to F- cells
replicon
71
what does F' plasmid carry?
bacterial DNA into new cells
72
what does Hfr cell produce?
F pilus
73
where does integrated F plasmid begin transfer of genes?
on one side of the origin of transfer of plasmid
74
All of/part of chromosome is transferred to recipient cell (choose one)
part of
75
chromosome usually _____ before complete transfer
breaks
76
recipient cell of chromosome transfer remains _____
F-, since incomplete F plasmid was transferred
77
there is a lot of ______ in gene pool of a single species
variation
78
less than ____ of E.coli genes found in all strains
50%
79
what is the core genome of a species?
the amount of genes of a particular species found in all strains of that species
80
the remaining parts of the core genome are termed _____
the mobile gene pool
81
the mobile gene pool can move from ____
one DNA molecule to another
82
examples of mobile gene pool/mobile genetic elements
plasmids, transposons, genomic islands, phage DNA
83
replicon that is independent of the chromosome and generally encodes only non-essential genetic information
plasmid
84
segment of DNA that directs its own movement to another location in chromosomal or plasmid DNA
transposon
85
large genomic segment in a cell's genome that originated in another species
genomic island
86
phage genome that sometimes carries additional genes
phage DNA
87
_______ common in microbial world
plasmids
88
plasmids are usually ____ with origin of replication
dsDNA
89
_______ generally encode nonessential information, but may allow survival in particular environment
plasmids
90
plasmids have _________ genes
few to many
91
low-copy-number
one or a few per cell
92
high-copy-number
many, up to 500
93
plasmids can have ______ to _______
low copy number to high copy number
94
most plasmids have ________; some replicate in many different species
narrow host range
95
plasmids in same compatibility group can/cannot be maintained in the same cell (choose one)
cannot
96
_______ requires conjugative plasmid for transfer
mobilizable plasmid
97
organisms in which antibiotic resistance is found
many
98
organisms in which antibiotic synthesis is found
streptomyces species
99
organisms in which gas vacuole production is found
halobacterium species
100
organisms in which increased virulence is found
yersinia and shigella species
101
organisms in which insect toxin synthesis is found
bacillus thuringiensis
102
organisms in which nitrogen fixation is found
rhizobium species
103
organisms in which oil degradation is found
psuedomonas species
104
organisms in which pilus synthesis is found
e.coli, pseudomonas species
105
organisms in which toxin production is found
bacillus anthracis
106
organisms in which tumor formation in plants
agrobacterium species
107
what can bacteria conjugate with?
plants
108
what causes crown gall?
agrobacterium tumefaciens
109
what happens with crown gall?
cells multiply without hormones and produce opine
110
tumor-inducing (Ti) plasmid is called
T-DNA (transferred DNA)
111
where is T-DNA incorporated?
plant chromosome
112
tumor formation genes can be replaced with _________ and incorporated into plant genome
beneficial genes
113
what are R plasmids?
resistance plasmids
114
what do resistance plasmids do?
encode resistance to antimicrobial medications
115
many resistance plasmids are ______
conjugative plasmids with broad host range
116
resistance plasmids can spread their resistance to ______ quickly
medications
117
normal microbiota with R plasmids may transfer them to _______
pathogens
118
what do transposons provide mechanism for?
moving DNA
119
where can transposons move into?
other replicons in the same cell
120
simplest transposon mechanism is ______
insertion sequence (IS)
121
what does the insertion sequence do?
encodes only transposase enzyme, inverted repeats
122
what type of transposon includes one or more genes?
composite transposons
123
composite transposons integrate via __________
non-homologous recombination
124
specific case: transposons yielded vancomycin-resistant Staphylococcus aureus strain. list the steps of how this occurred
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
list the characteristics encoded by genomic islands
use of specific energy sources, acid tolerance, ability to cause disease
126
nucleotide composition of genomic islands are very different from genome. what is the base pair ratio characteristic for each species?
G-C base pair ratio
127
what are pathogenicity islands?
a distinct class of genomic islands acquired by microorganisms through horizontal gene transfer
128
_________ degrade foreign DNA
restriction-modification systems
129
what cuts DNA at a specific sequence in a restriction-modification system?
restriction enzyme
130
how do modification enzymes protect the cell's own DNA?
by adding methyl groups
131
include small segments of phage DNA that recognize the specific DNA if it invades the cell again
CRISPR systems
132
what is the first invasion of a CRISPR system?
complex of Cas proteins cuts DNA into short fragments
133
what happens to the short fragments of DNA after the first invasion of a CRISPR system?
the fragments are inserted into chromosome at CRISPR array
134
what is an integrated DNA fragment called?
a spacer
135
_______ is transcription of CRISPR array that generates crRNAs that direct DNA-cutting enzymes to invading DNA
subsequent invasion
136
what does CRISPR stand for?
clustered regularly short palindromic repeats
137
what are CRISPR derived from?
bacteriophage that have previously infected the cell (are used to detect and destroy DNA from bacteriophages during subsequent infections)
