Organisms use DNA Repair Systems to Counteract Mutations Flashcards

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1
Q

what enzyme catches 99% errors in DNA repair by proofreading

A

DNA Polymerase

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2
Q

what mechanism may be activated to cope with errors that remain after proof reading e.g base-base mismatches, small insertions, deletions

A

mismatch repair mechanism (MMR)

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3
Q

e.g of some cancers MMR defects are found in

A

leukemias
lymphomas
ovary/prostate

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4
Q

when does post replication repair respond

A

after damaged DNA has escaped repair and failed to be completely replicated

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5
Q

how might DNA polymerase leave an unreplicated gap on newly synthesised strand

A

may stall at lesion and skip over it

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6
Q

what protein creates matching gap on donor strand that can be filled by repair synthesis

A

RecA protein

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7
Q

what’s the repair that reverses UV damage called

A

photo reactivation repair

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8
Q

how can UV damage to E. coli DNA be partially reversed

A

if cells are exposed to visible light (mostly blue range)

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9
Q

what enzyme does photoreactivation repair need

A

photolyase protein

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10
Q

what must the photolyase enzyme do to cleave thymine dimers bonds

A

absorb a photon of blue light

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11
Q

who lacks photo reactivation repair

A

humans

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12
Q

what are the 3 steps of base mechanisms involved in excision repair

A

damage/error is recognised and clipped out
DNA polymerase adds nucleotides
DNA ligase seals

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13
Q

what clips out error, leaving gap on 1 side of helix

A

an endonuclease

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14
Q

what end of the clipped DNA does DNA polymerase add nucleotides to

A

free 3’OH end

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15
Q

what enzyme closes the gap in base and nucleotide excision repair

A

DNA ligase

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16
Q

2 types of excision repair

A

base excision repair

nucleotides excision repair

17
Q

what recognises an inappropriately paired base in 1st step of base excision repair

A

DNA glycosylases

18
Q

what do DNA glycosylases first do in base excision repair

A

cut glycosidic bond between target base sugar, forming an apurrinic/apyrimidic site

19
Q

what enzyme recognises sugar with missing base and makes cut in phosphodiester backbone of site

A

AP endonuclease

20
Q

what does nucleotide excision repair repair

A

bulky DNA regions that alter/ distort double helix

21
Q

briefly explain nucleotides excision repair in humans

A

proteins recognise damaged dna and recruit more repair proteins to site
forms excision repair complex to remove long DNA fragment with lesion in from strand
gap filled by DNA polymerase + sealed by DNA ligase