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Biochemical Regulation > Mutations and DNA Repair > Flashcards

Mutations and DNA Repair Flashcards

0
Q

Deamination of adenine results in ____________ which base pairs with ________________.

A

Hypoxanthine, cytosine

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1
Q

Causes of DNA mutation

A
  1. Mistakes made in DNA replication

2. Mutations made by chemical and physical damage to DNA

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2
Q
  1. Mutations made by chemical and physical damage to DNA
A
  1. Hydrolysis= a basic site
  2. Deamination by HNO2
  3. Deamination by H2O
  4. Oxidative damage
  5. Alkylation of bases
  6. Cross linking
  7. Strand damage
  8. Intercalating agents
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3
Q

Cytosine deaminated to

A

Uracil

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4
Q

3 mechanisms of deamination

A

Removal of NH2

  1. Hydrolysis
  2. Hydrolysis=> abasic site
  3. Nitrous acid HNO2
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5
Q

Sodium disulfite deaminated 5-methylcytosine to

A

Thymine

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6
Q

T or F

Sodium disulfite deaminates cytosine

Therefore

A

False
Sodium disulfite does NOT deaminate cytosine

Therefore sodium disulfite can be used to gauge amount of methylated DNA

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7
Q

Guanine deaminated to

A

Xanthine (still base pairs with cytosine, but only with 2 H-bonds instead of 3)

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8
Q

Are purines or pyrimidines more susceptible to abasic site formation by hydrolysis?

A

Purines. AG

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9
Q

Oxidative damage is caused by

A
  1. ROS
  2. Electron transport chain ETC
  3. Metabolic products
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10
Q

Most common deamination by hydrolysis

A

C to U

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11
Q

Oxidative damage: 8-oxoG is mutagenic because

A

8-oxoG anti bps with C anti (3 H bonds )
Normal relative to G anti bps with C anti (3H bonds)

8-oxoG(syn)z=A(anti)
Mutagenic relative to
T(anti)=A(anti) /
G(anti) 3 H-bonds C(anti)

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12
Q
  1. Mistakes made in DNA replication
A
  1. Proofreading error = transition/ transversion
  2. Indel= frameshift
  3. DNA microsatellites= polymorphisms, polyQ
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13
Q

Oxidative damage: _______ is mutagenic

A

8-oxoG

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14
Q

Alkylation of bases: A,G purines

A

C8

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15
Q

Alkylation of bases: C,T pyrimidines

A

C5, C6

16
Q

Alkylation of bases: product of

A

Smoke-> process C molecules in liver

17
Q

Ames test

A
  1. Control- natural bg f of rev mutants by playing on min His media
  2. Salmonella + potential mutagen on filter paper in middle of plates (treat w rat liver enzymes)
  3. Large clear zone = more potent mutagen ; more colonies that grow outside clear zone = more mutagenic substance

Salmonella = His auxotrophs
Revertant mutants
Test in animal sys to determine if carcinogenic

18
Q

Intercalating agents cause ______________________________ possibly bc of ___________ or ______________

A

Insertion / deletion mutations
DNAP ( or RNAP) slippage
Distortion to DNA structure

19
Q

Damage by gamma radiation and x rays generates

A
  • Free radicals and ROS
  • dsDNA breaks that prevent replication
  • replication for stalls, collapses
20
Q

X rays are more severe than

A

Solar radiation

21
Q

Damage by gamma radiation and x rays: nick in 1 strand fragments how many chromosomes?

A

1

22
Q

Damage by gamma radiation and x rays: nick in 2 strands fragments how many daughter chromosomes?

A

2/ both

23
Q

Cross linking by solar radiation: UV light =

A
  1. Cyclobutane thymine dimers
    2 covalent bonds
    (Affects adjacent pyrimidines)
    (No H-bonding with complementary strand)
  2. 6,4- Photoproduct
    1 diagonal bond between C6 and C4 of adjacent thymines
    Conformation change in DNA backbone stalls polymerase which most commonly falls off or goes through the thymine dimer Photoproduct = mutation
24
Q

Direct repair (no base removal) of methylated bases: Single use enzyme

A

Methyltransferase (transfers methyl from O6-methylguanine to its cys, targeting it for degradation)

25
Q

Base excision repair

A

Remove DNA
Occurs after replication

Functions on single damaged bases that distort DNA very little

Repair unligatable single strand nicks

26
Q

BER in bacteria

A
  1. Glycosylase= remove base
  2. AP endonuclease= ss nick
  3. Pol I = 5’-> 3’ exonuclease
  4. Ligase seals nick
27
Q

BER in eukaryotes

A
  1. Glycosylase= remove base
  2. AP endonuclease= ss nick
  3. Pol
  4. Flap endonuclease
  5. Ligase seals nick
    = long patch

OR

  1. Pol Beta (5’-dRP lyase)
  2. Pol beta synthesizes 1 base
  3. Ligase seals nick
    = short patch

Biochemical Regulation (5 decks)

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