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Molecular Biology > Mod 8- Causes Of DNA Mutation & DNA Repair > Flashcards

Mod 8- Causes Of DNA Mutation & DNA Repair Flashcards

1
Q

What is a mutation?

A

An alteration in the nucleotide sequence of a DNA molecule.

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2
Q

What are spontaneous mutations?

A

Mutations that result from errors in DNA replication.

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3
Q

What causes strand-slippage during DNA replication?

A

Regions of DNA containing many copies of small repeated sequences.

This is when it loops out to add or remove a nucleotide (causing frame shift)

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4
Q

What is base tautomerism?

A

A phenomenon where a DNA polymerase is tricked by isomers with slightly different chemical structures.

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5
Q

What is an important base analog used in mutation studies?

A

5-bromouracil (5bU).

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6
Q

What does 5-bromouracil (5bU) mimic?

A

Thymine.

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7
Q

What is the consequence of enol-5bU pairing incorrectly during replication?

A

It pairs with G instead of A.

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8
Q

What are mutagens?

A

Chemical or environmental agents (radiation/ UV light) that cause changes in DNA molecules.

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9
Q

What is the effect of deaminating agents on adenine?

A

Deamination of adenine gives hypoxanthine, which pairs with C not T.

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10
Q

What does deamination of cytosine produce?

A

Uracil, which pairs with A not G.

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11
Q

What are alkylating agents?

A

Agents that add alkyl groups to nucleotides.

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12
Q

Name an example of an alkylating agent.

A

Ethylmethane sulphonate (EMS).

Causes transition mutation

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13
Q

What type of mutation do intercalating agents cause?

A

Insertion mutations.

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14
Q

What is an example of an intercalating agent?

A

Ethidium bromide.

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15
Q

What type of DNA damage is caused by ultraviolet radiation?

A

Causes bases to interact with themselves

Base dimerization- bases connect to each other

Photoproducts.

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16
Q

What is an AP site?

A

Apurinic, apyrimidinic site resulting from the detachment of bases.

17
Q

How often does depurination or depyrimidination occur?

A

About 1000 times a day.

18
Q

True or False: Thymine can be deaminated.

A

False.

19
Q

Fill in the blank: Deamination of guanine gives _______.

A

xanthine.

This blocks DNA replication as it can’t base pair with anything

20
Q

What effect does heat have on DNA?

A

Causes detachment of bases, leading to an AP site.

21
Q

What is the primary importance of DNA repair?

A

Preserving the composition and coding potential of the genome

22
Q

What is direct repair in the context of DNA mutations?

A

An enzyme corrects a nucleotide alteration caused by a mutagen

23
Q

Which enzyme in E. coli can remove alkyl groups from nucleotides?

A

ADA enzyme

Removes alkyl groups attached to position 4 of T and position 6 of G

24
Q

What is the function of the MGMT enzyme in humans?

A

Removes alkyl groups from position 6 of G

25
Q

What type of DNA damage can be repaired by DNA photolyase in E. coli?

A

Base dimers formed by UV radiation

26
Q

What is the nucleotide excision repair system?

A

Damaged nucleotide is removed and the gap is filled by DNA synthesis

27
Q

What are the two types of excision repair?

A
  • Base excision repair- a single altered base is removed
  • Nucleotide excision repair- a longer piece of DNA containing the altered bases is removed
28
Q

How does base excision repair happen in E. coli?

A

Begins with removal of the damaged base by a DNA glycosylase enzyme

Heat gives rise to an AP site

AP site is then filled

29
Q

What does AP stand for in the context of DNA damage?

A

Apurinic, apyrimidinic site

30
Q

What enzyme carries out nucleotide excision repair in E. coli?

A

UvrABC endonuclease

The region containing the damaged nucleotide is excised and resynthesised

31
Q

What distinguishes the parent strand from the daughter strand during mismatch repair in E. coli?

A

The parent strand is methylated

32
Q

Which enzymes recognize mismatches in E. coli?

A
  • MutH
  • MutS

The mismatch is excised and the DNA is resynthesised

33
Q

How does mismatch repair in humans differ from that in E. coli?

A

Humans do not involve methylation and use MutS-like proteins for mismatch recognition

34
Q

What is the role of telomeres in nonhomologous end joining?

A

Mark the natural ends of chromosomes

35
Q

What happens during nonhomologous end joining in humans?

A

DNA ligase joins the two ends together

36
Q

What are the 2 ways in which mutagens can cause mutations?

A
  1. Base analogs = mutagenic chemicals that look like bases and are incorporated into the DNA
  2. Direct structural change = DNA is physically changed by environmental factor
37
Q

What are deaminating agents?

A

Remove the NH2 group

Change the structures of some nucleotides

38
Q

What are intercalating agents?

A

Inserted between base pairs

39
Q

What is mismatch repair?

A

Corrects errors in DNA replication

Parent strand contains correct nucleotide
Daughter strand contains the mismatch

Molecular Biology (10 decks)

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