Mutation and Repair of DNA Flashcards Preview

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Flashcards in Mutation and Repair of DNA Deck (46):
1

substitution

changes from a single base pair to another

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indel mutation

deletion or insertion of one or several base pairs

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tautomeric shifts

A;C base paring in rare imino form
G;T base pairing in rare enol form
movement of H atoms

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transitition

pyrimidine-pyrimidine or purine-purine

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transversion

pyrimidine-purine or vice versa

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silent mutation

no change in amino acid

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neutral mutations

function is not affected - change to similar a.a

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mis-sense mutation

results in different a.a

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non-sense mutation

results in a stop codon

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open reading frame (ORF)

nucleotides flanked by a start codon and one of the stop codons

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frameshift

insertion or deletion of 1 or 2 base pairs alters the reading frame of the gene distal to the site of mutation

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factors influencing spontaneous mutations

accuracy of DNA replication machinery
efficiency of mechanisms
degree of exposure to mutagenic agents

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UV light

excites nucleotides

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X-rays

ionization

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Ionizing radiation

breaks chromosomes

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UV irradiation

hydrolysis of cytosine to cytosine hydrate (causes mis-pairing)
cross-linking of thymine to form thymine dimers (blocks DNA replication)

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Chemical mutagens

alkylating agents
5-bromouracil
proflavin
nitrous acid
hydroxylating agent

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alkylating agents

mustard gas, ethyl methane sulfonate, ethyel ethan sulfonate
donate alkyl group - error prone DNA repair process

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5BU

substitute for base

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acridine dyes

frameshift mutations
carry (+) charges
alter rigidity and spacing of the DNA double helix
causes insertion or deletion of 1 or more nucleotides in replicated DNA

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nitrous acid

de-amination of bases
sodium nitrate (NaNO3) converted to nitrous acid (HNO2) in the stomach
C to U mutation

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germinal mutation

in germ-lone cells will be transmitted through gametes to the offspring

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somatic mutation

in somatic cells will only be observed in descendants of that cell and will not be transmitted to the next generation

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spontaneous mutation

without a known cause due to errors in the metabolic pathway or unknown agents in the env.

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induced mutation

exposure of an organism to a mutagen

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forward mutation

wild-type allele to mutant allele

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reverse mutation

restores original phenotype

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back mutation

2nd mutation at same site of 1st

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suppressor mutation

2nd mutation and different site that reverts the changes phenotype due to the 1st mutation

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suppressor tRNA

recognize a different codon in the mRNA but still provide the same a.a of the original tRNA - amber

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iso-alleles

no or minor effects on the phenotype

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null alleles

results in no gene product or gene products are non-functional

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recessicve lethal mutation

affect genes required for growth - lethal in homozygous state

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auxotrophs

unable to synthesize an essential nutrient - grow only when essential metabolites are supplemented

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temp-sensitive

grow at lower temps. but not at higher temps.

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suppresor-sensitive

viable only when a 2nd mutation is present

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DNA repair mechanisms in E. Coli

light-dependent repair
excision repair
mismatch repair
post-replication repair
error-prone repair

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Photolyase

cleaves cross link in thymine dimers using energy derived from blue light

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DNA repair endonuclease

recognizes, binds to, excises damaged bases

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DNA polymerase

fills in the gap

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DNA ligase

seals the break

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Base exicision repair

removes abnormal bases

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Nucleotide exicision repair

removes large defects

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Exonuclease

uvrA, uvrB, uvrC

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uvrB

bends DNA at thymine dimer

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uvrC

cleaves off 12 nucleotides flanking the thymine dimer