lecture 7, chapter 8 Flashcards
(129 cards)
1
Q
through ______, organisms adapt to ever-changing environments
A
natural selection
2
Q
what are the two general mechanisms that bacteria use to adjust to new circumstances?
A
regulation of gene expression, genetic change
3
Q
what is often used as a model system of genetic change?
A
E. coli
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
5
Q
what are the two mechanisms of genetic change in bacteria?
A
mutation and horizontal gene transfer
6
Q
what is mutation?
A
changes in existing nucleotide sequence
7
Q
what is horizontal gene transfer?
A
movement of DNA from one organism to another
8
Q
changes are passed to progeny by _________
A
vertical gene transfer
9
Q
changes in organism’s DNA alters _________
A
genotype
10
Q
changes in genotype often changes ______
A
phenotype
11
Q
phenotype is also known as
A
observable characteristics
12
Q
phenotype is also influenced by _______
A
environmental conditions
13
Q
genotype is ______
A
sequence of nucleotides in DNA
14
Q
the bacteria of a genotype are _____, meaning ______
A
haploid, there is only one copy with no backup
15
Q
what does the deletion of gene for tryptophan biosynthesis yield?
A
a mutant that only grows if tryptophan is supplied
16
Q
if growth factor is required, mutant is termed ______
A
auxotroph
17
Q
auxo means _____
A
increase
18
Q
troph means _____
A
nourishment
19
Q
proto means _____
A
first
20
Q
_______ does not require growth factors
A
prototroph
21
Q
geneticists compare mutants to _____
A
wild type
22
Q
wild-type E.coli strain is ______
A
prototroph
23
Q
what are strains designated by?
A
three-letter abbreviations
24
Q
three-letter abbreviation for streptomycin resistance
A
Str^R
25
three-letter abbreviation meaning "cannot make tryptophan"
Trp^-
26
genetic changes that result from normal processes
spontaneous mutations
27
spontaneous mutations occur ______
randomly at infrequent, but characteristic rates
28
probability of mutation per cell division
mutation rate
29
what is the mutation rate typically between for a given gene?
10^-4 to 10^-12
30
what are mutations passed to?
progeny
31
mutations are most frequently the result of ______
unrepaired replication errors
32
what is it called when a mutation occasionally changes back to it's original state?
reversion
33
when does reversion occur?
spontaneously at low frequencies
34
_______ does not cause mutations, but selects cells that grow under its conditions
environment
35
large populations such as cells in a colony contain _____; not all cells are identical
mutants
36
what is more likely, a single mutation or a two mutations at the same time?
a single mutation.
single mutations are rare enough, but two mutations at the same time are even more unlikely
37
why might physicians give two antimicrobial medications simultaneously?
to reduce resistance
38
an organisms that has mutated to become resistant to an antimicrobial medication will _______
become dominant in an environment where the medication is present
39
chance that a cell will become resistant to both antimicrobial medications is ________
the product of mutation rate for each gene
40
what is the most common spontaneous mutation?
base substitution
41
______ is change of a single base pair
point mutation
42
what is the following mutation? incorrect nucleotide incorporated during DNA synthesis
base substitution
43
what are the three possible outcomes of base substitution?
silent (synonymous) mutation, missense mutation, nonsense mutation
44
silent (synonymous) mutation introduces _______
wild-type amino acid
45
missense mutation introduces ________
a different amino acid
46
does the resulting protein of a missense mutation function normally?
No
47
nonsense mutation specifies _____
stop codon
48
what does a nonsense mutation yield?
shorter, often non-functional protein
49
for deletion/addition of nucleotides, what does the impact depend on?
the number of nucleotides involved and location within protein
50
how many pairs changes one codon?
three
51
the deletion/addition of one or two pairs results in _____
frameshift mutation
52
what do frameshift mutations often result in?
premature stop codon; leading to shortened, nonfunctional protein
53
in what mutation is a different set of codons translated?
frameshift mutation
54
pieces of DNA that can move from one location to another in a cell's genome; process of transposition
transposons (jumping genes)
55
gene into which transposon jumps is inactivated; function disrupted
insertional inactivation
56
most transposons have _____
transcriptional terminators
57
what do transcriptional terminators in transposons block?
expression of downstream genes in operon
58
induced mutations result from ______
outside influence
59
any substance that increase the spontaneous mutation rate is a ______
mutagen
60
what does a mutagen induce?
a mutation
61
geneticists may use mutagens to ______
increase the mutation rate
62
what are the two general types of mutagens?
chemical agent, radiation
63
what are the three types of chemical mutagens?
chemicals that modify nucleobases, base analogs, intercalating agents
64
what are the two types of radiation mutagens?
ultraviolet (UV) light, x-rays
65
what is the action of chemicals that modify nucleobases?
chemical modification change base-pairing properties of nucleobases
66
base-pairing properties differ from ______
those of nucleobases normally found in DNA
67
where do intercalating agents insert?
between adjacent base pairs in a DNA strand, pushing them apart
68
where do transposons insert?
randomly into DNA, into cell's genome
69
what does ultraviolet light cause?
thymine dimers to form
70
what do x-rays cause?
single and double strand breaks in DNA
71
what is the result of chemicals that modify nucleobases
nucleotide substitution
72
what is the result of base analogs?
nucleotide subsitution
73
what is the result of intercalating agents?
addition or subtraction of nucleotides
74
what is the result of transposons?
insertional inactivation
75
what is the result of ultraviolet light?
errors during repair process
76
what is the result of x-rays?
deletions
77
chemicals that modify nucleobases increase chance of _____
incorrect nucleotide incorporation
78
alkylating agents add ______ onto nucleobases
alkyl groups
79
_______ adds methyl group to guanine
nitrosoguanidine
80
when a methyl group is added to guanine, the resulting methylguanine may base-pair with ______
thymine
81
base analogs resemble
nucleobases
82
why do base analogs differ from nucleobases?
they have different hydrogen-bonding properties
83
base analogs can be incorporated into DNA by _______
DNA polymerase
84
in base analogs, where is the wrong nucleotide incorporated into?
complementary strand during DNA replication
85
what does 5-bromouracil resemble?
thymine
86
what does 5-bromouracil often base-pair with?
guanine
87
what does 2-amino purine resemble?
adenine
88
what does 2-amino purine often pair with?
cytosine
89
intercalating agents increase _______
frameshift mutations (leading to errors during replication)
90
structure of intercalating agents
flat molecules
91
what happens when an intercalating agent is in a template strand?
a base pair is added to synthesized strand
92
what happens if an intercalating agent is in a strand being synthesized?
a base pair is deleted
93
intercalating agents often result in _____
a premature stop codon
94
what are thymine dimers
covalent bonds between adjacent thymines
95
what can ultraviolet light cause?
distortion of molecule, replication and transcription stall
96
mutations due to UV light results from _____
cell's SOS repair mechanism
97
double-strand breaks as a result of x rays can be ____
lethal
98
what can x-rays alter?
nucleobases
99
________ can be introduced intentionally to generate mutations
transposons
100
_______ generally inactivates gene into which it inserts
transposon
101
what happens if damaged DNA is not repaired?
cell death; cancer in animals
102
why are mutations rare?
because alterations in DNA generally repaired before being passed to progeny
103
in humans, two genes associated with breast cancer code for DNA repair enzymes. what is the result of mutations in either gene?
high probability of breast cancer
104
during replication, _______ sometimes incorporates the wrong nucleotide
DNA polymerase
105
mutations is prevented by _____
repairing before DNA replication
106
what are the two mechanisms of repair?
proofreading and mismatch repair
107
what is proofreading done by?
DNA polymerase
108
what can DNA polymerase do during proofreading?
checks accuracy, can back up and remove incorrect nucleotide, inserts correct nucleotide
109
is DNA polymerase perfect at proofreading?
no, but it is very efficient
110
what fixes errors missed by DNA polymerase?
mismatch repair
111
steps of mismatch repair
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
_______ of DNA indicates template strand
methylation
113
newly synthesized strand is ______
unmethylated
114
modified nucleobases lead to _____
base substitutions
115
steps of modified nucleobase repair
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
what is photoreactivation?
light repair
117
photoreactivation is only found in _____
bacteria
118
in photoreactivation, ____ uses energy from light
enzyme
119
what does photoreactivation break?
covalent bonds of thymine dimer
120
what is excision repair?
dark repair
121
in excision repair, _____ removes damage
enzyme
122
in excision repair, after the enzyme removes damage, what occurs?
DNA polymerase, DNA ligase fill in and seal the gap
123
last-ditch repair mechanisms used when other systems fail
SOS repair
124
when is SOS repair induced?
following extensive DNA damage that stalls DNA and RNA polymerases
125
how many genes are in SOS system?
several dozen
126
SOS system includes a _______ that synthesizes even in extensively damaged regions
DNA polymerase
127
why are errors made in SOS system?
because the DNA polymerase in the SOS system has no proofreading ability
128
errors made during SOS repair results in _____
SOS mutagenesis
129
