MBG 2040 > mutations > Flashcards

mutations Flashcards

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1
Q

What happenes when DNA damage is not corrected

A
  • there is an inherited change in genetic information (a mutation)
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2
Q

true or false - all mutations are created equal

A

false

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3
Q

mutation

A

a heritable change in the sequence of an organisms genetic material
- may alter the phenotype
- the process by which genetic change occurs

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4
Q

mutant

A

an organism that carries one or more mutations in its genetic material

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5
Q

mutation and evolution

A
  • mutations are the source of all genetic variation
  • natural selection preserves combinations best adapted to the existing environment
  • recombination between homologous chromosomes in meiosis rearranges genetic variability into new gene combinations
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6
Q

somatic mutations

A

occur in somatic cells
- passed to new cells through mitosis
- will not be transmitted to the progeny

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7
Q

germinal mutations

A

occur in germ line cells
- passed to new cells through meiosis
- will be passed to about 1/2 progeny who will carry the mutation in all their cells

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8
Q

bacterial and phage mutants

A
  • useful in genetic studies because they reproduce fast
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9
Q

point mutations

A

occur at localized sites in DNA
3 main types…
- base substitution
- frameshift mutation
- tautomeric shifts

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10
Q

dynamic mutation

A

when the nucleotide repeat copy can expand or contract dramaticaly

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11
Q

gross chromosomal rearrangement

A

a change in chromosome number or structure

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12
Q

base substitution

A

change in one base with a different base
- transition: replaces a pyrimidine with another pyrimidine (or purine with purine)
- transversion: replaces a pyrimidine with a purine (or visa versa)

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13
Q

frame shift

A

insertion or deletion of one or two base pairs alter the reading frame of the gene distal to the site of the mutation
- protein sequences change dramatically

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14
Q

tautomer

A

different arrangements of the same molecule - usually with H atoms

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15
Q

tautomeric shift

A

movement of H atoms from one position in a purine or pyrimidine base to another
- rare, can occur spontaneously during DNA replication where they alter DNA base pairing

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16
Q

rare A:C and G:T base pairing

A
  • occurs due to tautomeric shifts
  • when the bases are in their enrol or imino states
  • A and C create 2 H-bonds
  • G and T create 3 H-bonds
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17
Q

expanding nucleotide repeats

A
  • during DNA replication a hairpin forms on the newly synthesized strand, part of the template is replicated twice
  • the 2 strands of the new DNA molecule separate and the strand with the extra codon copies serves as a template for replication
  • expansion of triplet repeats is the cause of numerous human diseases
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18
Q

forward mutation

A

genetic alteration that changes the wild-type phenotype to mutant

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19
Q

reverse mutation

A

changes the mutated site back to normal

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20
Q

missense mutation

A

a base substitution that results in an amino acid change in the protein
- change in a codon

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21
Q

nonsense mutation

A

a base substitution at the 3rd codon position that changes a sense codon to one of the three stop codons
- stops translation
- position of the mutation determines length of the protien

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22
Q

silent mutation

A

a base substitution at the 3rd codon position that changes the codon to one still specifying the same amino acid
- doesn’t affect the overall protein

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23
Q

neutral mutation

A
  • missense mutation where the amino acid is changed to one of a similar chemical type
  • little to no effect on protein function
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24
Q

a loss-of-function mutation

A
  • cause complete or partial loss of normal protein function
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25
gain-of-function mutation
causes the cell to produce a protein or gene product whose function is not normally present
26
conditional mutation
expressed only under certain conditions (ex. temp sensitive)
27
lethal mutation
causes premature cell death
28
suppressor mutation
a second site mutation that hides or suppresses the effect of a first mutation (reverse it)
29
intragenic suppressor
- suppressor mutation that occurs in the same gene - when a missense mutation alters a single codon a second mutation at a different site in the same gene may restore the original amino acid
30
intergenic suppressor
- suppressor mutation present within a different gene
31
internal factors of mutations
- spontaneous - something has gone wrong in the cell itself - most DNA damage is caused by internal factors generated by normal metabolic processes
32
external factors of mutation
- induced - such as chemicals and the environment
33
what can damage DNA inside the cell
- water (hydrolysis) - oxygen (oxidation) - alkylating agents (alkylation)
34
what can cause spontaneous DNA damage
- DNA replication errors - DNA replication pausing - Endogenous chemical reactions
35
DNA replication error: tautomeric shift
- causes spontaneous DNA damage - movement of H atoms in a base results in non-standard base pairing
36
DNA replication error: wobble-induced base mispairing
- flexibility in base-pairing (wobble) can result in non standard GT and AC base pairs
37
DNA replication error: strand slippage during replication
- occurs in repeated DNA sequences and misalignments during recombination
38
DNA replication pausing
- replication stalling at a DNA nick - generated by ROS or enzymes like topoisomerase - double-stranded break (DSB) is a lethal or mutagenic lesion unless properly repaired by recombination mechanisms
39
endogenous chemical reactions: depurination
- spontaneous loss of a purine base through hydrolysis of a glycosidic bond (A is lost more often than G) - loss of a pyrimidine base is less common - leave an AP site - during replication, single-stranded DNA containing an AP site is susceptible to replacement with A or C generating transition or transversion mutations
40
endogenous chemical reactions: deamination
- spontaneous loss of -NH2 group on DNA bases, causes transition mutations -
41
endogenous chemical reactions: oxidation
- ROS damage DNA - can produce oxidized bases which frequently mispairs with C or A to produce transversion mutations (G:C to A:T)
42
endogenous chemical reactions: alkylation
endogenous alkylating agents can add methyl groups to DNA bases
43
Induced DNA damage
- results from exposure to known mutagens - such as chemical agents and radiation
44
categories of chemical-induced mutations
- chemicals that are mutagenic to both replicating and non-replicating DNA - chemicals that are mutagenic only to replicating DNA
45
chemical mutagens affect replicating and non-replicating DNA
- alkylating agents - nitrous acid - hydroxylamine - base analogs - acridines
46
alkylating agents
- mutagens that react with DNA bases and add methyl or ethyl group - directly or indirectly induce transitions, trans versions or frameshifts
47
nitrous acid
- delaminating agent - removes amino NH2 from DNA bases A, C and G, cause transition mutations
48
hydroxylamine
- hydroxylates the NH2 group of cytosine causing the modified base to pair with adenine after replication
49
base analogs
- two common base analogs are 5-bromouracil and 2-aminopurine - incorporated into DNA during replication - don't change bases themselves but they look like alternate bases
50
acridines
- intercalation of an acridine dye causes a frameshift mutation during DNA replication - long aromatic compounds that slip between bases and cause DNA backbone to become buckled - it is no longer straight causing polymerase to slip and mess up
51
mutations induced by radiation
- uv light induces mutations through excitation - x-rays induce mutation through ionization
52
mutagenesis by ultraviolet irradiation
- forms thymine dimers which block DNA replication - can cause DNA breaks - can lead to skin cancer - damages vitamin D
53
mutagenesis by X-rays
- ionizing radiation can cause DNA breaks - result in changes in chromosome structure - causes nicks in DSB in chromosomes - faulty repair can cause gross chromosomal rearrangements such as deletions, duplications, inversions and translocations
54
DNA repair mechanisms
- direct reversal of DNA damage - excision repair - mismatch repair - recombination - translation DNA polymerases
55
direct reversal of DNA damage
1. light-dependent repair: direct repair of thymine dimers by the enzyme photolyase (only in prokaryotes) 2. enzymatic removal of alkyl groups from DNA bases 3. ligation of single-stranded nicks in DNA
56
excision repair
- DNA repair endonuclease recognize, bind to and excises the damaged bases - a DNA polymerase fills in the gap using undamaged complementary strand of DNA as a template - DNA ligase seals the break (nick) left by DNA polymerase 2 kinds... 1) base excision repair 2) nucleotide excision repair
57
base excision repair
- recognizes and repairs DNA bases damaged by deamination, alkylation or oxidation
58
nucleotide excision repair
-removes thymine dimers and other bulky forms of DNA damage - enzyme complex recognizes distortion, strands are separated and damaged part is removed, short tract DNA synthesis takes place
59
mismatch repair (MMR)
- recognizes a mismatched base in the newly synthesized DNA through hemimethylated GATC sequence - an exonuclease removes a portion of the new DNA that includes the incorrect base - DNA poly !!! fills in the longer gap and ligase seals the nick - mismatch is always associated with unmethylated
60
Recombination DNA repair mechanism
- have important roles in repairing spontaneous or induced DNA double-stranded breaks (DSB) 2 types... - homologous (HR) - non-homologous (NHEJ)
61
homologous recombination repair
- occurs during or after DNA replication - if one sister chromatid suffers DSB it can be repaired using an identical sister chromatid - used to ensure proper chromosome separation during meiosis - can result in accurate repair or potential loss of homozygosity
62
non-homologous recombination repair
- available throughout eukaryotic cell cycle - provides a mechanism for T:T to be by-passed so that replication can continue - non-homologous end joining repairs double-stranded breaks and can result in loss of homozygosity due to lost sequences
63
translesion synthesis DNA polymerases
- recruited to replicate through the DNA damage, bypassing the lesion, normal DNA replication is to follow - TLS DNA polymerases replicate inaccurately, get error-prone DNA synthesis at site of the original blocking lesion
64
SOS response of TLS DNA polymerases
- DNA is heavily damaged - involves the activation of a host DNA recombination, DNA repair and DNA replication proteins - increases chance of cell survival but with an increased frequency of replication errors
MBG 2040
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