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Genetics 311 > Chapter 19: DNA Mutation & Repair (Exam 3) > Flashcards

Chapter 19: DNA Mutation & Repair (Exam 3) Flashcards

(60 cards)

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1
Q

Depurination

A

cause of spontaneous mutation, removal of purine base from G or A

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2
Q

Deanimation

A

cause of spontaneous mutation, removal of amino group from cytosine base, DNA repair enzymes can recognize U as inappropriate and remove it, if repair system fails, C-G to A-T mutation will result in subsequent replication

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3
Q

Deamination of 5-methyl cytosine

A

cause of spontaneous mutation, thymine is normal constituent of DNA –> poses problem for repair enzymes, cannot determine which of two bases is incorrect –> hotspot for mutation

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4
Q

tautomeric shift

A

cause of spontaneous mutation, temporary change in base structure, rare, promote AC and GT bp, must occur immediately prior to DNA replication for mutation to occur

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5
Q

Mutagens

A

involved in development of human cancers, cause gene mutations that can impact future generations

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6
Q

Classifications of mutagens

A

chemical or physical

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7
Q

Chemical mutagens

A

alter DNA structure directly, base modifiers, intercalating agents

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8
Q

Base modifiers

A

covalently modify structure of a nucleotide

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9
Q

Example of base modifer

A

Nitrous Acid, replaces amino groups with keto groups

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10
Q

Intercalating Agents

A

contain flat planar structures that intercalate themselves into a double helix –> distorts helical structure –> daughter strands may have single nucleotide additions or deletions

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11
Q

Example of intercalating agent

A
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12
Q

Base analog

A

engineered to look like DNA bases but not nearly as stable, become incorporated into daughter strands during DNA replication

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13
Q

Example of base analogs

A

5-bromouracil, thymine analog, incorperated into DNA, causes incorrect base pairing, AT to GC

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14
Q

Classifications of physical mutations

A

ionizing radiation and non-ionizing radiation

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15
Q

two categories of physical mutagens

A

ionizing radiation and nonionizing radiation

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16
Q

examples of ionizing radiation

A

x-rays, gamma rays

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17
Q

properties of ionizing radiation

A

short wavelength, high energy, penetrates deeply into biological tissues (can reach gametes)
creates chemically reactive molecules: free radicals

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18
Q

what can free radicals cause

A

base deletions
single nicks in DNA strand
cross-linking
chromosomal breaks

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19
Q

examples of nonionizing radiation

A

UV light

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20
Q

properties of nonionizing radiation

A

less energy, cannot penetrate deeply
causes formation of cross-linked thymine dimers

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21
Q

thymine dimers

A

cause mutations when DNA strand is replicated
only occur at T-T sites
polymerase cannot read the TT, has to guess

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22
Q

DNA repair

A

cells contain several DNA repair systems
usually a multistep process

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23
Q

Steps of DNA repair

A
  1. irregularity in DNA detected
  2. abnormal DNA removed
  3. normal DNA synthesized (using DNA polymerase)
  4. DNA ligase seals new DNA to original strand
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24
Q

Types of DNA repair

A

direct repair
base excision repair (BER)
nucleotide excision repair (NER)
mismatch repair
homologous recombination repair
nonhomologous end joining

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25
direct repair
not multistep damaged bases can be directly repairs covalent modifications of nucleotides can be reversed by specific enzymes
26
two enzymes that can direct repair
photlyase and alkyltransferace
27
photylase
repairs thymine dimers
28
alkyltransferace
removal of methyl group
29
base excision repair (BER)
uses enzymes known as DNA N-glycosylases: can recognize abnormal base and cleaves bond between it and the sugar in DNA A pendalases- nick backbone
30
what can BER repair
thymine dimers, uracil
31
steps of BER
1. DNA N glycosylase cleaves base 2. a penadalase nicks backbone 3. DNA polymerase removes base
32
DNA excision repair (NER)
repairs many types of DNA damge: thymine dimers, missing bases, chemically modified bases, some crosslinks found in all eukaryotes and prokaryotes
33
NER four key proteins (in E. coli)
UvrA, UvrB, UvrC, UvrD involved in UltraViolet light Repair recognize and remove short segment of DNA DNA polymerase and ligase complete repair
34
diseases caused by defects in NER
xeroderma pigmentosum (XP) cockayne syndrome (CS) increased sensitivity to sunlight leads to incurable skin cancer
35
mismatch repair systems
detect and correct a base pair mismatch found in all organisms specific to newly synthesized strand
36
base mismatch
structure of DNA double helix obeys AT/GC base pairing during replication, an incorrect base can be added DNA polymerase have 3' - 5' proofreading ability which usually corrects mismatched bases
37
proteins in mismatch repair (in E. coli)
MutL, MutH, MutS detect mismatch and remove it from strand can distinguish between parental and daughter strands: prior to replication, both strands methylated immediately after replication, parental methylated but daughter is not cut the non-methylated (newly synthesized) strand
38
double-strand breaks
very dangerous, breakage of chromosome into pieces caused by ionizing radiation and chemical mutagens occur 10-100x every day in every cell in humans cause chromosomal rearrangements and deficiencies
39
repair systems for double-strand breaks
homologous recombination repair (HRR) nonhomologous end joining (NHEJ)
40
homologous recombination repair (HRR)
results in some recombined DNA precise repair Steps: 1. double strand breaks 2. processes/removes 3' ends 3. sister chromatid acts as template using strand exchange 4. DNA polymerase synthesizes DNA
41
nonhomologous end joining (NHEJ)
not precise, lose some DNA does not require sister chromatid nearby 1. double strand breaks 2. protein binds ends 3. proteins fill gap and synthesize new strand
42
repair of activley transcribed genes
repaired more efficiently than non transcribed genes, easier to access transcription makes DNA more susceptible to damage more likely to be important for survival of organism
43
mutations
heritable change in genetic material provide allelic variations foundation for evolutionary change cause of diseases
44
types of mutations
chromosome, genome, single gene
45
point mutation
change in single base pair transition: change of a pyrimidine (C. T) to another pyrimidine or a purine (A, G) to another purine transversion: change of pyrimidine to purine / vise versa
46
silent mutation
base substitution that does not change amino acid sequence
47
missense mutation
base substitution that does change amino acid sequence
48
nonsense muation
change normal codon to a stop codon
49
frameshift mutation
addition or deletion of nucleotides in multiples of 1 or 2, change reading frame
50
up promoter mutations
make promoter more like consenus sequence, increase rate of transcription
51
down promoter mutation
make promoter less like consensus sequence, decrease rate of transcription
52
chromosomal rearrangement
may break the gene itself or alter expression because of new location (position effect)
53
reasons for position effects
movement next to regulatory sequence, movement into heterochromatic region
54
germ line mutations
occur directly in sperm or egg cell (or a precursor) passed through generations
55
somatic mutations
occur in a body cell individual with somatic mutation referred to as genetic mosaic not passed on
56
mutation rate
likelihood that a gene will be altered by a new mutation expressed as number of new mutations in a given generation range of 10^-5 - 10^-9 per generation
57
things that effect mutation rates
larger genes have greater chance locations that are more susceptible (hot spots)
58
spontaneous mutation
result from abnormalities in cellular/biological processes
59
induced mutations
caused by environmental agents
60
mutagen
agents known to alter DNA structure

Genetics 311 (6 decks)

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