Chapter 8 Flashcards
(127 cards)
1
Q
Bacteria have two general mechanisms to adjust to new
circumstances
A
➢ Regulation of gene expression
➢ Genetic change
2
Q
Two mechanisms of genetic change in bacteria
A
- Mutation
- Horizontal gene transfer
3
Q
changes in existing nucleotide sequence
A
Mutation
4
Q
movement of DNA from
one organism to another
A
Horizontal gene transfer
5
Q
change in the nucleotide sequence of the cell
A
Mutation
6
Q
Changes are passed on to the next generation by
A
vertical gene transfer
7
Q
movement of DNA from one
organism to another, which are then passed on to the next generation
A
Horizontal gene transfer
8
Q
favors those with greater fitness
A
Natural selection
9
Q
Change in organism’s DNA alters
A
genotype
10
Q
Change in genotype often change observable
characteristics, or
A
phenotype
11
Q
what can also change organism’s phenotype
A
Mutations
12
Q
“increase”
A
Auxo
13
Q
“nourishment”
A
troph
14
Q
Growth factor required
A
auxotroph
15
Q
does not require growth factors
A
Prototroph
16
Q
“first”
A
Proto
17
Q
Geneticists compare mutants to
A
wild type
18
Q
are random genetic changes that results from normal cell processes
A
Spontaneous mutations
19
Q
A gene mutates spontaneously at an infrequent characteristic
rate
A
Mutation rate
20
Q
probability that a mutation will occur in a gene
A
Mutation rate
21
Q
what is the Mutation rate
A
Typically between 10–4 and 10–12 for a given gene
22
Q
Occasionally change back to original state
A
reversion
23
Q
does environment cause mutations
A
no
24
Q
selects cells that can grow under its conditions
A
Environment
25
most common type of mutation
Base substitution
26
type of Base substitution
Point mutation
27
is change
of a single base pair
Point mutation
28
Incorrect nucleotide
incorporated during
DNA synthesis
Base substitution
29
possible outcome of Base substitution
* Silent/synonymous mutation:
* Missense mutation:
* Nonsense mutation:
30
Base substitutions more common where
in aerobic environments
31
wild-type amino acid
[Does not alter protein function]
Silent/synonymous mutation
32
different amino acid
[Resulting protein may only partially function]
Missense mutation
33
creates a stop codon
[Yields shorter often a non-
functional protein]
Nonsense mutation
34
Impact depends on number of nucleotides and location
within protein
Deletion or addition of nucleotides
35
3 nucleotides change how many codons
1
36
1 or 2 nucleotides yields what
frameshift mutation
37
Piece of DNA that can move from one location to another in
cell’s genome
Transposons (jumping genes)
38
Inserted DNA disrupts function of gene
insertional inactivation
39
Blocks expression of downstream genes in operon
transcriptional terminators
40
result from outside influence
Induced mutations
41
Agent that induces change is
mutagen
42
types of mutagen
chemical and radiation
43
Chemicals that modify nucleobases
* Change base-pairing properties
Chemical Mutagens
44
what do Chemical Mutagens increase
chance of incorrect nucleotide during DNA replication
45
resemble nucleobases
But have different hydrogen-bonding properties
Base analogs
46
Can be mistakenly incorporated onto DNA by DNA polymerase
Base analogs
47
Wrong nucleotide is incorporated into complementary strand during DNA replication
Base analogs
48
cause frameshift mutations
Intercalating agents
49
* Flat molecules that intercalate (insert) between adjacent
base pairs in DNA strand
* Pushes nucleotides apart, produces space
* Increases chance of addition or deletion during replication
Intercalating agents
50
Transposons can be introduced intentionally to
generate
mutations
51
Transposon inserts into cell’s
genome
52
two types used as mutagens of radiation used as mutagens
Ultraviolet light
X rays
53
causes thymine
dimers
Ultraviolet light
54
what does Ultraviolet light stall
Replication and transcription stall at
distortion
55
Mutations result from cell’s SOS
repair mechanism in response to
Ultraviolet light damage
56
cause single- and double-
strand breaks in DNA
➢Double-strand breaks often lethal
X-rays
57
are rare because of DNA repair
Mutations
58
During replication, DNA polymerase sometimes
incorporates
wrong nucleotide
59
Mispairing slightly distorts
DNA helix
60
Mutation prevented by
repairing before DNA
replication
61
Two mechanisms of repair
1) Proofreading by DNA polymerase
2) Mismatch Repair
62
* Verifies accuracy
* Can back up, excise nucleotide
* Very effective but not perfect
1) Proofreading by DNA polymerase
63
* Fixes errors missed by DNA
polymerase
* Enzyme cuts sugar-phosphate
backbone of new DNA strand
* Another enzyme degrades
short region of DNA strand with
error
* DNA polymerase, DNA ligase
fill in and seal the gap
2) Mismatch Repair
64
can lead to base substitutions if not repaired
Modified nucleobases
65
DNA glycosylase removes
damaged nucleobase
Base excision repair
66
degrades short section to remove damage then synthesizes
replacement
DNA polymerase
67
light repair
* Enzyme uses energy from visible light
* Breaks covalent
Photoreactivation
68
dark repair
* Enzyme removes damaged region
* DNA polymerase and DNA ligase fill in and seal the gap
Nucleotide excision repair
69
Last-effort repair mechanism used when other systems fail
SOS Repair
70
rare even when mutagens are used, difficult to isolate
mutants
71
Two main approaches of mutant
* Direct selection
* Indirect selection
72
cells inoculated onto medium that supports growth of mutant but not parent
Direct selection
73
Replica plating which indirectly selects auxotrophs
Indirect selection
74
Selectively kills prototrophs
Penicillin Enrichment
75
added before cells are plated on nutrient agar to create master plate
Penicillinase
76
cause many cancers; most are mutagens
Carcinogens
77
measures effect of chemical on reversion rate of histidine-requiring Salmonella auxotroph
Ames test
78
f chemical is what reversion rate increases relative to
control (more colonies grow)
mutagenic
79
Microorganisms commonly acquire genes from
other cells:
horizontal gene transfer (HGT)
80
Demonstration of Horizontal Gene Transfer
- 2 bacterial strains are used
- Strains are mixed on a glucose-salts agar plate
- Colonies form only if cells of one strain acquired genes from the other strain.
81
Genes naturally transferred by three mechanisms
Transformation
Transduction
Conjugation
82
naked DNA uptake from the environment by bacteria
Transformation
83
bacterial DNA transfer by viruses
Transduction
84
DNA transfer during cell-to-cell contact
Conjugation
85
replicates as a unit
replicon
86
must be integrated into a replicon to be reproduced
DNA fragments
87
replaces complementary region of the recipient cell’s DNA
Donor DNA
88
uptake of “naked” DNA
Transformation
89
physiological state that allows the cell to take up DNA
competent
90
binds to receptor on surface of
the competent cell
A double-stranded donor DNA
encoding streptomycin resistance (StrR)
91
steps of DNA-Mediated Transformation
* A double-stranded donor DNA
encoding streptomycin resistance (StrR) binds to receptor on surface of
the competent cell
* One strand enters the cell; nucleases degrade other strand
* New DNA integrates into chromosome by homologous recombination
* One daughter cell will inherit donor DNA
* Transformed cell grows on a medium containing streptomycin
* Other donor genes are possible
92
transfer of bacterial genes by
bacteriophages
Transduction
93
types of Transduction
Specialized transduction:
Generalized transduction:
94
specific genes
Specialized transduction
95
any genes of donor cell
Generalized transduction
96
* Rare error during phage assembly
* Transfer of bacterial DNA to new bacterial host
Generalized transduction
97
DNA transfer between bacterial cells; plasmid or chromosome transfer
Conjugation
98
direct their own transfer from donor to recipient
Conjugative plasmids
99
Conjugation steps
1) Making contact
2) Initiating transfer
3) Transferring DNA
4) Transfer complete
100
is integrated into chromosome via homologous recombination
F plasmid
101
results when small piece of
chromosome is removed with F
plasmid DNA
F plasmid
102
produces F pilus
Hfr cell
103
Part of chromosome transferred to
recipient cell
104
remains F– since
incomplete F plasmid transferred
recipient cell
105
Consists of three sets of genes
pan-genome
106
three sets of genes
Core genome
accessory genome
Unique genes
107
is common to all strains
Core genome
108
is present in more than one but not all strains
accessory genome
109
are found in only one
strain of the species).
Unique genes
110
can move from one DNA molecule to another
Mobile genetic elements
111
Usually circular double stranded DNA with origin of replication
Plasmids
112
Plasmids usually encode what
nonessential information
113
carry all genetic information for transfer
Conjugative plasmids
114
requires conjugative plasmid for transfer
Mobilizable plasmid
115
provide mechanism for moving DNA
Transposons
116
large DNA segments in genome
that originated in other species
Genomic islands
117
Certain types of phages can insert their DNA into the
host cell chromosome
Phage DNA
118
becomes part of the host cell’s genome
Phage DNA
119
Such phage DNA is called a
prophage
120
cuts DNA at specific sequence
Restriction enzyme
121
protects cell’s own DNA by adding methyl groups
Modification enzyme
122
clusters of regularly interspersed short palindromic repeats
CRISPR systems
123
complex of Cas proteins cuts DNA into short fragments
First invasion
124
another name for Phage DNA,
spacer DNA
125
is inserted into a chromosomal region, called CRISPR, and provides record of infection
spacer DNA
126
transcription of CRISPR array
generates crRNAs
Subsequent invasion
127
bind to Cas proteins
crRNAs
