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Molecular Biology 2040 > DNA Repair > Flashcards

DNA Repair Flashcards

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1
Q

Why are there so little mutations?

A
  1. DNA repair mechanisms require double stranded DNA (as one is being replicated complementary strand is acting as a wild type for repair)
  2. DNA has built in redundancy (repaired by many repair systems)
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2
Q

What does Mismatch Repair (MMR) fix?

A

replication errors, mispaired bases, strand slippage

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3
Q

How does MMR differentiate between old and new strand?

A

old strand has methyl groups attached to it

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4
Q

Where does MMR degrade strand?

A

between the nick and mismatched bases

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5
Q

Hows does polly and ligase fill the gap that was degraded?

A

using the old strand as a template

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6
Q

What happens if there’s a mutation in the MMR?

A

Cancer

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7
Q

Direct Repair

A

Pyrimidine Dimers *fixes not removing, no cutting!!

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8
Q

Direct Repair - What breaks the covalent bond in dimers?

A

Photoreactivation of UV induced pyrimidine dimers

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9
Q

Direct Repair - What removes the methyl group restoring it to guanine (G->A transition)

A

O6 methylguanine DNA transferase

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10
Q

Base Excision repair

A

abnormal bases

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11
Q

Base excision repair - What removes damaged bases creating an apyrimidinic/apurinic site?

A

DNA glycosylase

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12
Q

Base excision repair - what cleaves the phosphodiester bond on 5’ side of AP site?

A

AP endonuclease

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13
Q

Base excision repair - What adds new nucleotides to the exposed 3’OH group?

A

DNA polly

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14
Q

Base excision repair - DNA ligase seals…restoring the original sequence?

A

the nick in the sugar phosphate backbone

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15
Q

Nucleotide excision repair

A

distorts double helix

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16
Q

Nucleotide excision repair - What do enzymes do?

A

scan the DNA for distortions and the the DNA is separated

17
Q

Nucleotide excision repair - What bonds are cleaved on either side of the mutation?

A

Phosphodiester bonds

18
Q

Nucleotide excision repair - What is the damaged strand removed by? What is the gap filled by? What are the ends sealed by?

A

helicase, DNA polly, ligase

19
Q

Double stranded breaks

A

Stalls DNA replication and leads to chromosome rearrangements

20
Q

Double stranded breaks - HDR

A

homologous recombination uses genetic info contained in sister chromatid resulting in 2 holliday junctions

21
Q

Double stranded breaks - NHEJ

A

during G1 phase of cell (no sister chromatid) - important role in somatic recombination and generating antibody diversity

Molecular Biology 2040 (8 decks)

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