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Genes > DNA Repair > Flashcards

DNA Repair Flashcards

1
Q

How can damaged be induced?

A

Spontaneously = depurination and deamination
Mutagen-induced

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2
Q

What are the different mutagen0induced DNA damaged?

A

Pyrimidine dimers
Alklylation
Substitution, deletion, insertion
Frameshift mutations
Double-strand breakd

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3
Q

What are the two types of point mutation?

A

Transition
Transversion

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4
Q

What is a transition point mutation?

A

Purine or pyrimidine is replaced by another of the same kind

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5
Q

What is a transversion point mutation?

A

Purine or pyrimidine is replaced by the other kind

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6
Q

What do hydrolytic attacks cause?

A

Depurination
Deamination

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7
Q

What is depurination?

A

Loss of purine base = A&G from DNA leaving a abasic site

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8
Q

What happens if depurination and deamination is left uncorrected?

A

Lead to deletion or substitution of base pairs during DNA replication

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9
Q

What happens in deamination?

A

Deamination of bases in DNA yields unnatural nucleotides

These unnatural nucleotides, which can be directly recognized and removed by specific DNA glycosylases

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10
Q

What does deamination of C produces what?

A

C&raquo_space;> U which can be repaired by uracil DNA glycosylase

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11
Q

What is the role of nitrous acid?

A

Oxidatively deaminates primary amines = producing transition mutations

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12
Q

How is C converted to T?

A

Cytosine is methylated to 5-methyl cytosine
5-methyl cytosine deaminated to T

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13
Q

What can happen when cells are exposed to UV radiation?

A

Formation of a dimer = between 2 pyrimidine bases

Occurs between two adjacent T or C

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14
Q

Name alkylating agents

A

Nitrogen mustard
EMS
MNNG

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15
Q

What are alkylating agents?

A

Chemical that add an alkyl group to another molecule

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16
Q

What problems can nitrogen mustard cause?

A

N mustard can cross-link w DNA at N7 position of G

Results in chromosome break

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17
Q

What happens to guanine bases when exposed to EMS and MNNG?

A

EMS yiels O6-ethylguanine
MNNG yields O6-methylguanine

Both of which can pair with T (instead of C)

18
Q

What mutations do intercalating agents cause?

A

Insertion and deletion mutations = frameshift mutations

19
Q

How do intercalating agents work?

A

They increase the distance between 2 consecutive base pairs

Replication of such DNA generates deletion or insertion of one or more nucleotides int eh newly synthsized DNA

20
Q

Give an example of intercalating agent

A

Ethidium bromide binds to DNA

21
Q

Missense vs Nonsense mutation

A

A missense mutation is a type of point mutation in which a single nucleotide change in the DNA sequence leads to the substitution of one amino acid for another in the protein sequence.

A nonsense mutation is a type of point mutation in which a single nucleotide change in the DNA sequence introduces a premature stop codon (nonsense codon) into the mRNA transcript.

22
Q

What does the Ames test assess?

A

Mutagenicity of compounds

23
Q

How does the Ames test work?

A

The bacteria is a auxotroph = meaning it cannot make Histidine so needs it to grow

Mix the test compound (potential mutatgent) and bacteria together

If there are colonies growing, the test compound is a mutagen

Need a control to compare basal mutation level

24
Q

Name repair pathways for DNA synthesis error

A

Proofreading by DNA polymerase (exonuclease)
Mismatch repair (mutSLH)

25
Q

Name repair of DNA modifications

A

Direct reversal of damage (photoreactivation repair)
Excision repair = base or nucleotie
By DNA glycosylase or apurinic/apyrimidinic (AP)

26
Q

Name repair of replication fork barriers

A

Translesion synthesis

27
Q

Name repair of breakd in DNA

A

Repair double-strand breaks by
Homologous recombination
Non-homlogous end joining

28
Q

What happens in proofreading?

A

3’ to 5’ exonuclease
Checks from the newest base added
If incorrect, removes it

29
Q

What is the job of midmatch repair?

A

Correct errors that remain after proofreading

30
Q

How does mismatch repair work in E.coli?

A

MutH endonuclease makes a nick on 5’ side of unmethylated GATC (newly synthesized)
UvrD (helicase) and exonuclease removes defective strand
Unmethylated strand is corrected by DNAp III

31
Q

What does Dam methylase do?

A

Enzyme found in bacteria that adds a methyl group to the adenine base in the DNA sequence GATC

32
Q

What does photoreactivation repair do?

A

Removes pyrimidine dimers = C + T

33
Q

How does photoreactivation repair work?

A

Occurs only in bacteria
PHOTOLYASE = photoreactivation enzyme
Cleaves bonds between pyrimidine = light-dependent reaction

34
Q

What enzymes are needed for base excision repair (BER)?

A

DNA glycosylase cleaves the glycosidic bond = leaving apurinic or apyrimidinic site

AP endonuclease cleave the phosphodiester backbone at AP site

DNAp I and DNA ligase = restore base

35
Q

What does nucleotide excision repair require to function?

A

ATP and UvrA-D

36
Q

How does nucleotide excision repair occur?

A

UvrAB recognize damage
UrvBC nicks DNA
Urv D unwinds the marked region

37
Q

Why might nucleotide excision repair be needed and what diseases are caused without it?

A

UV-induced DNA lesions

Xeroderma pigmentosum and Cockayne syndrome = unable to repair UV-induced DNA lesions

38
Q

When is translesion DNA synthesis or ‘Error-prone repair’ used?

A

When a lesion is encountered during replication = DNAp III is replaced by error-prone translaesion DNAp
Pol IV or V

39
Q

What does the translesion DNAp do?

A

Extend DNA synthesis beyond the T dimer independent of base pairing
Has no proofreading exonuclease activity

40
Q

What is non-homologous end joining and how does it work?

A

Accidental ds-break = loss of nucleotides due to degradation from end joining

End recognition by KU heterodimers

Deletion of DNA sequence = emergency repair

41
Q
A

Genes (6 decks)

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