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genetics > chapter 11 part 1 > Flashcards

chapter 11 part 1 Flashcards

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1
Q

germ-line mutations

A

mutations that occur in germ-line cells (give rise to sperm/egg)

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2
Q

how are germ-line mutations passed on

A

from one generation to the next

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3
Q

somatic mutations

A

mutations in cells not in the germ line

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4
Q

how are somatic mutations passed on

A

somatic cells divides by mitosis, only direct descendants carry mutation

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5
Q

what do gene mutations do to DNA base pairs

A

substitute, add, or delete one or more DNA base pairs

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6
Q

point mutations

A

localized mutations that occur at specific, identifiable position in a gene

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7
Q

mutation hotspots

A

genes with elevated mutation rates

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8
Q

characteristics of mutation hotspots

A
  • large gene size
  • regions rich in CpG dinucleotides
  • long stretches of trinucleotide repeats
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9
Q

ex. of mutation hotspots

A
  • DYS gene (Duchenne muscular dystrophy)
  • NF1 gene (nuerofibromatosis)
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10
Q

base-pair substitution mutations

A

replacing one nucleotide with another

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11
Q

transversions

A

base-pair substitution going from purine to purine or pyrimidine to pyrimidine

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12
Q

transitions

A

base-pair substitution going from pyrimidine to purine or reverse

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13
Q

3 types of base-pair substitutions

A
  1. silent (synonymous)
  2. missense
  3. nonsense
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14
Q

silent (synonymous) mutation

A

no amino acid change

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15
Q

missense mutation

A

change in amino acid

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16
Q

nonsense mutation

A

creates stop codon

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17
Q

frameshift mutations

A

insertion or deletion of one or more base pairs altering reading from of the message

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18
Q

what are frameshift mutations also called

A

INDEL
- insertion or deletion

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19
Q

what is produced as a result of frameshift mutations

A

the wrong amino acid sequence and sometimes premature stop codons

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20
Q

promoter mutation

A

mutations that alter consensus sequence nucleotides of promoters

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21
Q

what do promoter mutations interfere with

A

efficient transcription initiation

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22
Q

what does efficient splicing of introns from mRNA require

A

specific sequences at either end of the intron

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23
Q

splicing mutation

A

mutation that results in splicing errors and production of mutant proteins due to retention of intron sequences in the mRNA

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24
Q

cryptic splice sites

A

when some base-pair substitutions produce new splice sites that replace/compete with authentic splice sites during mRNA processing

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25
polyadenylation mutations
mutation in polyadenylation signal sequence at 3' end of euk. mRNA that can block 3' processing
26
ex. of polyadenylation mutation
human B-globin gene - coding strand is mutated - Beverly reduces amount of functional protein produced
27
forward mutation
converse wild-type allele to a mutant allele
28
reverse mutations (reversions)
convert mutant alleles to wild-type or near wild-type
29
true reversion
wild-type DNA sequence or amino acid sequence is restored by a second mutation within the same codon
30
intragenic reversion
occurs through mutation elsewhere in same gene
31
second-site reversion
occurs by mutation in different gene and together the 2 mutations restore the organism to wild-type
32
what are second-site reversions also know as
suppressor mutations - second mutation suppresses mutant phenotype caused by first mutation
33
spontaneous mutations
arise in cells without exposure to agents capable of inducing mutation (mutagens)
34
how do spontaneous mutations arise
- errors in DNA replication - spontaneous changes in the chemical structure of a nucleotide base
35
why did DNA replication have high fidelity
due to accuracy of DNA polymerases, proofreading ability of DNA pol, and efficiency of mismatch repair
36
mismatches due to replication errors occur at rate of about ____________ in wild-type E. coli and same in euk.
1 x 10^-9
37
how do alterations in number of DNA repeats occur
strand slippage
38
strand slippage process
- DNA polymerase of replisome temporarily dissociates from template - portion of newly replicated DNA forms a temporary hairpin - resumption of replication leads to re-replication of some of the repeats and overall increase in number of repeats on daughter strand
39
trinucleotide repeat disorders
special class of mutations causing some hereditary diseases in humans and other organisms - increases number of characteristic trinucleotide repeats beyond certain threshold
40
depurination
loss of a purine from a nucleotide by breaking the covalent bond linking the nucleotide base to the sugar
41
apurinic site
lesion where deprivation occurs
42
when are most AP sites repaired
before replication
43
what happens when AP sites are left unrepaired
DNA pol will usually compensate by putting an adenine into the site during replication
44
deamination
loss of amino group from a nucleotide
45
what happens when cytosine is deaminated
an oxygen atom usually takes its place, converting the cytosine into uracil - DNA mismatch repair removed uracil from DNA and replaces it with cytosine to restore wild-type sequence
46
what happens when methylated cytosine is deaminated
- thymine base is produced - then base-pairs with guanine - mismatch repair system can restore wild-type G-C pair - if repair doesn't occur, replication will produce 2 sister chromatids, one w/ mutant A/T pair and one with wild G/C pair
47
induced mutations
produced by mutagens in an experimental setting to study types of damage caused, the mutation process itself, or repair responses to damage
48
mutagens
agents that cause DNA damage leading to mutations
49
chemical mutagens can be classified by their modes of action on DNA as:
1. nucleotide base analogs 2. deaminating agents 3. alkylating agents 4. oxidizing agents 5. hydroxylating agents 6. intercalating agents
50
DNA intercalating agents
distort DNA duplex by fitting between DNA base pairs - some form bulky adducts that contribute to distortion
51
what does distortion from intercalating agents lead to
DNA nicking that is not efficiently repaired, resulting in added or lost nucleotides
52
good DNA stains
- ethidium bromide - acridine orange
53
photoproducts
aberrant structures with additional bonds involving nucleotides caused by UV irradiation
54
pyrimidine dimers
produced by formation of one or two additional covalent bonds between adjacent pyrimidine nucleotides
55
ex. of 2 common photoproducts
1. thymine dimer 2. 6-4 photoproduct
56
thymine dimer
common photoproduct that is formed between the 5 and 6 carbons of adjacent thymines
57
6-4 photoproduct
formed by bond between carbon 6 on one thymine and carbon 4 on other
58
types of radiation
X-rays, gamma rays, radioactive materials
59
most serious damage caused by radiation
single-stranded or double-stranded breaks in DNA
60
what can breaks in DNA block
replication - health by with specialized repair systems
61
organisms preserver the fidelity of DNA using
multiple repair systems
62
what do multiple repair systems do
- directly repair DNA damage - allow organism to circumvent the problems caused by unrepaired damage
63
ex. of direct repair
- proofreading - photo reactive repair
64
proofreading activity of DNA polymerase leads to what kind of exonuclease activity?
3 to 5
65
how can pyrimidine dimers be directly repaired
photo reactive repair
66
can photo reactive repair take place in humans?
no
67
photo reactive repair process
- enzyme photolyase uses energy from visible light to break bonds between pyrimidine dimers - photolyase is encoded by E. coli phr (photo reactive repair) gene
68
how is DNA damage by alkylating agents repaired
enzymes that remove the added chemical groups, restoring the nucleotide to its normal form
69
what is direct repair of damage by alkylating agents performed by
class of enzymes called alkyltransferases
70
alkyltransferases
- remove alkyl groups (methyl/ethyl) - can reverse effects of EMS and NG
71
ex. of direct repair of damage by alkylating agents
- O6-methylguanine is converted by to guanine by enzyme O6-methylguanine methyltransferase - enzyme permanently inactivated after one such reaction
72
nucleotide base excision repair
multistep process that may repair damage to a nitrogenous base or replace an incorrect base
73
DNA glycosylases
series of enzymes that recognize specifically modified or incorrect bases and remove modified purine bases, leaving an AP site
74
base excision repair process
- DNA glycosylases work and create AP site - AP endonuclease creates single-stranded nick near the AP site - nick translation: DNA pol initiate removal/replacement of nucleotides, including AP site - DNA ligase seals the sugar-phosphate backbone
75
basic nucleotide excision repair process
1. enzymes recognize and bind to damaged region 2. segment of nucleotides is removed from the damaged strand 3. DNA pol fills in the gap and DNA ligase seals sugar-phosphate backbone
76
what is nucleotide excision repair often used to repair
UV-induced damage to DNA
77
what is nucleotide excision repair also known as
ultraviolet repair

genetics (47 decks)

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