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genetics > chapter 11 part 1 > Flashcards

chapter 11 part 1 Flashcards

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Biology 101 flashcards
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
Q

polyadenylation mutations

A

mutation in polyadenylation signal sequence at 3’ end of euk. mRNA that can block 3’ processing

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26
Q

ex. of polyadenylation mutation

A

human B-globin gene
- coding strand is mutated
- Beverly reduces amount of functional protein produced

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27
Q

forward mutation

A

converse wild-type allele to a mutant allele

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28
Q

reverse mutations (reversions)

A

convert mutant alleles to wild-type or near wild-type

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29
Q

true reversion

A

wild-type DNA sequence or amino acid sequence is restored by a second mutation within the same codon

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30
Q

intragenic reversion

A

occurs through mutation elsewhere in same gene

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31
Q

second-site reversion

A

occurs by mutation in different gene and together the 2 mutations restore the organism to wild-type

32
Q

what are second-site reversions also know as

A

suppressor mutations
- second mutation suppresses mutant phenotype caused by first mutation

33
Q

spontaneous mutations

A

arise in cells without exposure to agents capable of inducing mutation (mutagens)

34
Q

how do spontaneous mutations arise

A
  • errors in DNA replication
  • spontaneous changes in the chemical structure of a nucleotide base
35
Q

why did DNA replication have high fidelity

A

due to accuracy of DNA polymerases, proofreading ability of DNA pol, and efficiency of mismatch repair

36
Q

mismatches due to replication errors occur at rate of about ____________ in wild-type E. coli and same in euk.

A

1 x 10^-9

37
Q

how do alterations in number of DNA repeats occur

A

strand slippage

38
Q

strand slippage process

A
  • 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
Q

trinucleotide repeat disorders

A

special class of mutations causing some hereditary diseases in humans and other organisms
- increases number of characteristic trinucleotide repeats beyond certain threshold

40
Q

depurination

A

loss of a purine from a nucleotide by breaking the covalent bond linking the nucleotide base to the sugar

41
Q

apurinic site

A

lesion where deprivation occurs

42
Q

when are most AP sites repaired

A

before replication

43
Q

what happens when AP sites are left unrepaired

A

DNA pol will usually compensate by putting an adenine into the site during replication

44
Q

deamination

A

loss of amino group from a nucleotide

45
Q

what happens when cytosine is deaminated

A

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
Q

what happens when methylated cytosine is deaminated

A
  • 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
Q

induced mutations

A

produced by mutagens in an experimental setting to study types of damage caused, the mutation process itself, or repair responses to damage

48
Q

mutagens

A

agents that cause DNA damage leading to mutations

49
Q

chemical mutagens can be classified by their modes of action on DNA as:

A
  1. nucleotide base analogs
  2. deaminating agents
  3. alkylating agents
  4. oxidizing agents
  5. hydroxylating agents
  6. intercalating agents
50
Q

DNA intercalating agents

A

distort DNA duplex by fitting between DNA base pairs
- some form bulky adducts that contribute to distortion

51
Q

what does distortion from intercalating agents lead to

A

DNA nicking that is not efficiently repaired, resulting in added or lost nucleotides

52
Q

good DNA stains

A
  • ethidium bromide
  • acridine orange
53
Q

photoproducts

A

aberrant structures with additional bonds involving nucleotides caused by UV irradiation

54
Q

pyrimidine dimers

A

produced by formation of one or two additional covalent bonds between adjacent pyrimidine nucleotides

55
Q

ex. of 2 common photoproducts

A
  1. thymine dimer
  2. 6-4 photoproduct
56
Q

thymine dimer

A

common photoproduct that is formed between the 5 and 6 carbons of adjacent thymines

57
Q

6-4 photoproduct

A

formed by bond between carbon 6 on one thymine and carbon 4 on other

58
Q

types of radiation

A

X-rays, gamma rays, radioactive materials

59
Q

most serious damage caused by radiation

A

single-stranded or double-stranded breaks in DNA

60
Q

what can breaks in DNA block

A

replication
- health by with specialized repair systems

61
Q

organisms preserver the fidelity of DNA using

A

multiple repair systems

62
Q

what do multiple repair systems do

A
  • directly repair DNA damage
  • allow organism to circumvent the problems caused by unrepaired damage
63
Q

ex. of direct repair

A
  • proofreading
  • photo reactive repair
64
Q

proofreading activity of DNA polymerase leads to what kind of exonuclease activity?

A

3 to 5

65
Q

how can pyrimidine dimers be directly repaired

A

photo reactive repair

66
Q

can photo reactive repair take place in humans?

A

no

67
Q

photo reactive repair process

A
  • 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
Q

how is DNA damage by alkylating agents repaired

A

enzymes that remove the added chemical groups, restoring the nucleotide to its normal form

69
Q

what is direct repair of damage by alkylating agents performed by

A

class of enzymes called alkyltransferases

70
Q

alkyltransferases

A
  • remove alkyl groups (methyl/ethyl)
  • can reverse effects of EMS and NG
71
Q

ex. of direct repair of damage by alkylating agents

A
  • O6-methylguanine is converted by to guanine by enzyme O6-methylguanine methyltransferase
  • enzyme permanently inactivated after one such reaction
72
Q

nucleotide base excision repair

A

multistep process that may repair damage to a nitrogenous base or replace an incorrect base

73
Q

DNA glycosylases

A

series of enzymes that recognize specifically modified or incorrect bases and remove modified purine bases, leaving an AP site

74
Q

base excision repair process

A
  • 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
Q

basic nucleotide excision repair process

A
  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
Q

what is nucleotide excision repair often used to repair

A

UV-induced damage to DNA

77
Q

what is nucleotide excision repair also known as

A

ultraviolet repair

genetics (37 decks)

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