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Genetics - BIO 2306 > Ch 18 Gene Mutations & DNA Repair > Flashcards

Ch 18 Gene Mutations & DNA Repair Flashcards

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1
Q

a heritable change in the DNA sequence of genetic information

A

mutation

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2
Q

mutations that arise in somatic cells, which don’t produce gametes
mutation is passed on to all daughter cell, leading to clones

A

somatic mutations

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3
Q

mutations that arise in germ-line cells, which produce gametes and can be passed on to future generations

A

germ-line mutations

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4
Q

mutations that affect a single gene or locus
only detected by observing phenotypic effects

A

gene mutations

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5
Q

mutations that affect number or structure of chromosomes
can be deserved directly

A

chromosome mutations

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6
Q

alteration of a single nucleotide in the DNA

A

base substitution

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7
Q

what is a transition base substitution?

A

a purine is replaced by a different purine; a pyrimidine is replaced by a different pyrimidine

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8
Q

what is a transversion base substitution?

A

a purine is replaced by a pyrimidine; a pyrimidine is replaced by a different purine

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9
Q

what is a transversion base substitution?

A

a purine is replaced by a pyrimidine; a pyrimidine is replaced by a different purine

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10
Q

which arise more frequently? transitions or transversions? why?

A

transitions; easier to transform a base into its same type rather than a different one

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11
Q

one or more nucleotides added into DNA sequence

A

insertion

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12
Q

one or more nucleotides removed from DNA sequence

A

deletion

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13
Q

mutations that result in changes in the reading frame of a gene

A

frame-shift mutations

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14
Q

why do frameshift mutations generally have drastic effects on the phenotype?

A

frameshift mutations usually alter all amino acids encoded by the nucleotides following the mutation

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15
Q

insertions/deletions that do not change the reading frame

A

in-frame insertions / in-frame deletions

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16
Q

how do in-frame insertions/in-frame deletions arise?

A

insertions and deletions in multiples of 3 nucleotides leave the reading frame intact

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17
Q

mutations where the number of copies of a set of trinucleotides increases

A

expanding trinucleotides repeats

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18
Q

explain how expanding nucleotide repeats leads to anticipation

A

the more copies of the repeat present, the more likely the repeats will increase, and diseases caused by these expanding repeats become more severe in each generation

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19
Q

what trinucleotide sequence is most often present in most diseases caused by expanding trinucleotide repeats

A

CNG

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20
Q

explain how strand slippage can cause expansion of nucleotide repeats

A

During replication, DNA strands separate and begin replication. During replication, a hairpin may form on the newly synthesized strand, causing the sequence to be replicated twice, increasing the number of repeats on the new strand. In another round of replication of the new strand, the new DNA molecule contains addition copies of the repeated nucleotides

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21
Q

mutation that alters the wild-type phenotype

A

forward mutation

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22
Q

mutation that changes mutant back to wild-type phenotype

A

reverse mutation

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23
Q

mutation that results in a different amino acid in the protein

A

missense mutation

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24
Q

mutation that changes a sense codon into a stop codon, terminating translation

A

nonsense mutation

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25
Q

mutation that doesn’t change the amino acid sequence

A

silent mutation

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26
Q

missense mutation that alters the amino acid sequence of a protein but does not change its function

A

neutral mutation

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27
Q

mutation that causes the complete or partial absence of normal protein function

A

loss-of-function mutation

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28
Q

mutation that causes the cell to produce protein or gene product with a new function

A

gain-of-function mutation

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29
Q

mutations expressed only under certain conditions

A

conditional mutations

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30
Q

mutations that cause premature death

A

lethal mutations

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31
Q

mutation that hides the effect of another mutation at a nucleotide distinct from the original mutation site

A

suppressor mutation

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32
Q

explain how suppressor mutations are different than reverse mutations

A

suppressor mutations occur at a site different from the site of the original mutation, whereas a reverse mutation changes the mutated site back back to its original wild-type

33
Q

suppressor mutation that takes place within the same gene that contains the mutation being suppressed

A

intragenic suppressor mutation

34
Q

explain how intragenic suppressor mutations occur (three ways)

A

-suppressor may change a second nucleotide at a different site in the same gene to restore the original amino acid
-suppressor may suppress a frameshift mutations, by inserting or deleting a nucleotide
-making compensatory changes in the protein

35
Q

suppressor mutation that occurs in a gene different than the one with the original mutation that it suppresses

A

intergenic suppressor mutation

36
Q

explain how an intergenic suppressor mutation can occur

A

a second mutation that encodes for a tRNA that is capable of pairing with the original mutation’s codon

37
Q

the frequency with which a wild-type allele changes to a mutant allele

A

mutation rate

38
Q

list the three factors that affect mutation rates

A
  1. frequency that a mutation takes place
  2. probability a mutation is repaired
  3. probability mutation is detected
39
Q

mutations that arise from natural changes in DNA or replication errors

A

spontaneous mutations

40
Q

mutations that are caused by environmental agents, like chemicals or radiation

A

induced mutations

41
Q

explain how strand slippage causes a deletion

A

template strand of DNA loops out, resulting in a nucleotide being omitted on the newly synthesized strand

42
Q

explain how strand slippage causes an insertion

A

the newly synthesized strand loops out, resulting in an extra nucleotide being synthesized in the next round of replication

43
Q

explain how unequal crossing over causes insertions and deletions

A

when homologous chromosomes misalign, they crossover, and one chromosome has an insertion where the other has a deletion

44
Q

the loss of a purine base from a nucleotide

A

depurination

45
Q

how does depurination occur? what is produced?

A

the covalent bond connecting a purine to the 1’ carbon atom of deoxyribose breaks, producing an apurinic site

46
Q

a nucleotide that lacks its purine base

A

apurinic site

47
Q

what results from the presence of an apurinic site

A

since the apurinic site cannot act as a template for a complementary base during replication, an incorrect nucleotide (usually adenine) is incorporated in the new DNA strand

48
Q

a base substitution causes a mispaired base to be incorporated into a newly synthesized nucleotide chain

A

incorporated error

49
Q

the loss of an amino group from a base

A

deamination

50
Q

what results from deamination?

A

deamination can alter the pairing properties of a base, causing it to pair with a different nucleotide than it’s supposed to

51
Q

what occurs from the deamination of cytosine?

A

cytosine is turned into uracil, which then pairs with adenine
instead of a CG pair, a UA pair forms, which replicates into T*A

52
Q

any environmental agent that significantly increases the rate of mutation above the spontaneous rate

A

mutagen

53
Q

chemicals with structures similar to those of any of the four standard nitrogenous bases of DNA and can be incorporated into new DNA

A

base analogs

54
Q

explain how base analogs can cause mutations

A

base analogs can be incorporated into new DNA, instead of the standard base. the base analog may pair with the original complementary base, but it may also pair with a different base, causing a mutation

55
Q

molecules similar to the size of nucleotides that can sandwich themselves between adjacent bases in DNA

A

intercalating agents

56
Q

what are the effects of intercalating agents?

A

by intercalating between bases in DNA, the 3D DNA helix is distorted, causing insertions and deletions, thus producing frameshift mutations

57
Q

what are the effects of ionizing radiation from X-rays, gamma rays, cosmic rays, etc

A

they dislodge electrons from atoms, changing them into free radicals and reactive ions, which then alter structures of bases and break phosphodiester bonds, and frequently cause double-strand breaks in DNA

58
Q

what is the effect if UV light

A

UV light has less energy, and pyrimidines absorb UV light, resulting in the creation of pyrimidine dimers

59
Q

how do pyrimidine dimers form?

A

pyrimidines absorb UV light, causing chemical bond to form between two adjacent pyrimidines on the same DNA strand, which distorts the normal DNA configuration, often blocking replication

60
Q

DNA sequences that are capable of moving around in the genome

A

transposable elements (transposons_

61
Q

how can transposable elements cause mutations?

A

transposons insert themselves into a gene and disrupt it; or promote chromosome rearrangements

62
Q

what are the general characteristics of transposable elements (two of them)

A

short flanking direct repeats
terminal inverted repeats

63
Q

what are flanking direct repeats? how are they associated with transposons? how do they arise?

A

flanking direct repeats are short, directly repeated sequences (~3-12 bp) present on both sides of the transposon
they are not a part of the transposon
staggered cuts made in target DNA produced short single-stranded pieces of DNA on either side of transposon. replication of these ends produces the flanking direct repeats

64
Q

what are terminal inverted repeats and how are they associated with transposons?

A

terminal inverted repeats are sequences at both ends of a transposon that are inverted complements of one another

65
Q

why are terminal inverted repeats required for transposition?

A

enzymes catalyzing transposition recognize these sequences in order to locate the transposon

66
Q

movement of a transposable element from one location to another

A

transposition

67
Q

what are the three steps of transposition?

A
  1. staggered breaks made in target DNA
  2. transposable element joined to single-stranded ends of target DNA
  3. DNA is replicated at single-stranded gaps
68
Q

enzyme that makes single-stranded breaks in DNA during transposition, and is often encoded by the transposon

A

transposase

69
Q

transposable elements that transpose as DNA

A

DNA transposons

70
Q

transposable elements that transpose through an RNA intermediate

A

retrotransposons

71
Q

how does a retrotransposon move?

A

a transposable element (DNA) is transcribed into RNA, which is then copied back into DNA by reverse transcriptase

72
Q

new copy of transposable element moves to a new site while the original transposable element remains at its old site, therefore increasing the number of transposon copies

A

replicative transposition

73
Q

transposable element is excised from its original site and inserted into a new site, therefore no increase in transposon copies

A

nonreplicative transposition

74
Q

describe mismatch pair

A

incorrectly paired bases and small unpaired loops in DNA are detected and corrected by mismatch-repair enzymes
mismatch-repair enzymes used original DNA strand as template to correct the error

75
Q

how do mismatch-repair enzymes distinguish between the old and new strands of DNA (in bacteria)

A

old strands contain methyl groups (on the adenine nucleotides)

76
Q

describe direct repair

A

modified bases are restored back into their original (correct) structures

77
Q

describe base-excision repair

A

a modified base is excised, then the entire nucleotide is replaced

78
Q

describe nucleotide-excision repair

A

bulky lesions that distort the DNA double helix are removed, and any other DNA damage

Genetics - BIO 2306 (20 decks)

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