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Molecular Bio > Mod 8 - causes of DNA mutations + repair > Flashcards

Mod 8 - causes of DNA mutations + repair Flashcards

1
Q

what is a mutation?

A

an alteration in the nucleotide sequence of the DNA molecule

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2
Q

what is a spontaneous mutation?

A

a mutation resulting from an error in DNA replication
- not common - most DNA polymerases have very good proofreading activities

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3
Q

what is a tautomer?

A

an isomer with a slightly different chemical structure

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4
Q

what are the 4 normal bases?

A

amino-adenine (pairs with T)
keto-thymine (pairs with A)
keto-guanine (pairs with C)
amino-cystosine (pairs with G)

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5
Q

what are the 4 less common tatuomers?

A

imino-adenine (pairs with C) - i ate cheese
enol-thymine (pairs with G) - elephant trunk goat
enol-guanine (pairs with T) - eat good toast
imino-cytosine (pairs with G) - ice cold goo

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6
Q

what is a mutagen?

A

a chemical or environmental agent that can cause changes in DNA molecules

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7
Q

what is a base analog?

A

a mutagen that can be incorporated into DNA but causes different base pairing and causes a mutation to occur

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8
Q

what is 5-bromouracil?

A

a base analog of thymine
- has a Br broup instead of a methyl group on thymine

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9
Q

what is the difference between keto-5bU and enol-5bU ?

A
  • if keto-5bU is incorporated into replication instead of T, it binds to A - causes no change, is basically fine overall
  • if enol-5bU is incorporated into replication, it binds to G - basically changes an A to a G (bad)
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10
Q

what is a deaminating agent?

A
  • removes the amine group from a base
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11
Q

what happens when cytosine is deaminated?

A

gives uracil - pairs with A now

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12
Q

what happens when guanine is deaminated?

A

gives xanthine - blocks DNA replication

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13
Q

what happens when adenine is deaminated?

A

deamination of adenine gives hypoxanthine - doesn’t pair with T anymore - pairs with C now

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14
Q

what do alkylating agents do?

A

add alkyl groups e.g. ethylmethane sulphonate (EMS)
causes transition mutations

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15
Q

what do intercalating agents do?

A

inserts itself between base pairs (e.g. ethidium bromide)
causes insertion mutations

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16
Q

what does UV radiation do?

A

causes base dimerization
- attatches 2 bases together

17
Q

how does heat mutate DNA?

A
  • heat causes detatchment of bases - gives rise to an AP site
  • AP = apurinic, apyrmidinic (depurination or depyrmidiation)
18
Q

what are the 4 types of DNA repair?

A
  • direct repair
  • excision repair
  • mismatch repair
  • nonhomologous end-joining
19
Q

what is direct repair?

A

an enzyme corrects a nucleotide alteration caused by a mutagen
e.g. , MGMT enzyme in humans, ADA enzyme + DNA photolyase in e.coli

20
Q

what is excision repair?

A
  • damaged nucleotide is completely removed + gap is filled via DNA synthesis
21
Q

what are the 2 types of excision repair?

A
  • base excision repair - a single altered base is removed
  • nucleotide excision repair - a longer piece of DNA containing altered bases is removed
22
Q

describe the mode of action of UvrABC endonuclease (e.coli repairman)

A

Identification
- damaged nucleotide causes helix distortion
- UvrAB trimer attaches
- subunit UvrC attaches, UvrA detaches
Excision
- segment is excised by UvrB and UvrC
- UvrB bridges gap until DNA pol I and DNA ligase can repair the strand completely

23
Q

how can e.coli tell the difference between a template strand and daughter strands?

A
  • parent molecules are methylated
  • daughter strands are not yet methylated
24
Q

How does mismatch repair occur?

A
  • MutS and MutH attatch to the DNA
  • MutH then cuts the DNA
  • strand is removed by DNA helicase II
  • DNA pol I and ligase repairs strand
25
Q

how is mismatch repair different in ecoli vs in humans?

A
  • methylation not involved with humans
  • humans don’t have a MutS protein but do have another endonuclease protein
26
Q

what is the function of nonhomologous end-joining?

A

correct double-stranded DNA breaks

27
Q

how does nonhomologous end-joining occur in humans?

A
  • Ku proteins (molecular magnets) join to both ends of the double-strand break
  • Ku proteins attract one another + bring break together
  • DNA ligase joins two ends together

Molecular Bio (8 decks)

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