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Flow Of Genetic Information > DNA Damage And Repair > Flashcards

DNA Damage And Repair Flashcards

1
Q

What are the 4 types of DNA damage?

A

1) replication error
2) base tautomers
3) covalent damage
4) non-covalent interaction

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2
Q

What are base tautomers?

A

Base tautomers are alternative isomeric forms present for a small portion of time

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3
Q

What happens when an Enol group binds to a Thymine?

A

It’s becomes a base tautomer so it binds with G instead of A which can cause changes to the wrong base.

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4
Q

What is strand slippage?

A

Slippage is when there are some of the same bases but bind to wrong base causing an excess base to be outside

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5
Q

What is cytosine deamination?

A

Cytosine is subject to deamination to uracil.

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6
Q

What happens to create an Abasic sugar?

A

Loss of a base by hydrolysis so there is no base

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7
Q

What happens if guanine is oxidised?

A

Produces 8-oxo-G which pairs A instead of C leading to changes in pattern

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8
Q

Fact for ya init:

A

Alfotoxin B produced by peanut mould is activated by P450 in the liver is a reactive species that modifies guanine by mutations

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9
Q

What are intercalating agents?

A

They are usually aromatic rings that cause frame shift because the new polymerase insets another base

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10
Q

Name an intercalating agent?

A

Ethidium

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11
Q

Name 4 types of DNA repair?

A

Direct repair
Base excision repair
Nucleotide excision repair
Mismatch repair

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12
Q

what is direct repair?

A

Removes damaged bases

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13
Q

What is base excision repair?

A

Removes damaged base

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14
Q

What is nucleotide excision repair?

A

Removes damaged nucleotide

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15
Q

What is mismatch repair?

A

Excision of a long strand containing the mistake

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16
Q

How do flavoproteins repair DNA lesions?

A

Flavoproteins contain two light harvesting co-factors that in the presence of light release FADH free radicals that act as electron donor to break pyrimidine dimers

17
Q

What are DNA lesions?

A

They are thymine dimers caused by UV exposure

18
Q

How does UvrABC excinuclease removed thymine dimers?

A

UvrABC excinuclease cuts 8 bases on 5’ side and 4 bases on the 3’ side removing the dimer which is then sealed by Pol 1 and DNA ligase.

19
Q

How does nucleotide excision repair occur in prokaryotes?

A

A hetero dimer of 2xUvrA and 1 UvrB detect DNA damage UvrA is repaced by UvrC. UvrBC complex cuts out 8 bases on 5’ and 4bases on 3’. The gap is then filled by polymerase 1 and ligase.

20
Q

How is nucleotide excision repair done in eukaryotes?

A

XPC recognise the lesion allowing XPA+XPD to open and bind to DNA. Using RPA to stabilise the open complex. Then ERCC1-XPF and XPG create the incision to remove the oligonucleotide and pol 1 +ligase fill gap

21
Q

How is the deamination of cytosine to uracil repaired?

A

Uracil-N-glycosylase cuts the glycosidic bond. Ap ending lease cuts the back bone and pol 1 fills in by nick translation and ligase.

22
Q

What is the purpose of uracil-N-glycosylase?

A

To Remove U opposite G but also opposite A.

23
Q

How does uracil-N-glycosylase discriminate between U and T?

A

The base is flipped from inside to outside and if it fits like uracil would it would be cleaved.

24
Q

Wheat happens when there is a change in Keto group of G?

A

It becomes 8-oxo-G and binds to A instead of C

25
Q

What is the mechanism for mismatch repair?

A

MutS binds to the mismatch and mutH binds to DNA which is hemimethylated allowing for distinguishing of daughter and parent strand MutL links H and S. MutH then cuts unmethylated strands DNA segment.

26
Q

What is the SOS response?

A

This a response to damaged ssDNA this activates LexA which cleaves itself. In it’s cleaved form LexA increases transcription of repair proteins.

27
Q

What are the two types of double strand repair?

A

Homologous and non-homologous

28
Q

In double strand repair why isn’t it put on the end of chromosomes?

A

As they have telomeres that signal not to

29
Q

What is p53 arrest?

A

A tumour suppressor gene that holds cell cycle at G1/S phase if DNA is damaged. If irreparable can initiate apoptosis. If mutated can lead to cancer.

Flow Of Genetic Information (4 decks)

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