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Genetics Unit 4 > Lecture 2 strobel: mutations, mutagens and dna damage repair part 2 > Flashcards

Lecture 2 strobel: mutations, mutagens and dna damage repair part 2 Flashcards

1
Q

What are mutagens?

A

chemical or physical agents that induce mutations

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2
Q

What do mutagens do?

A

alter DNA in different ways

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3
Q

What do chemical mutagens contain?

A

base modifiers, base analogs and intercalating agents

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4
Q

What are base modifiers?

A

they are chemical mutagens that covalently modify the structure of a nucleotides base

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5
Q

What do base modifiers do?

A

can disrupt pairing by alkylating bases

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6
Q

What are base analogs?

A

modified nucleotides that fool DNA polymerase and become incorporated into DNA during replication
* incorporation of base analogs can distort DNA structure
* some tautomerize at a high rate

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7
Q

What are intercalating agents?

A

they can be inserted into the DNA double helix between bases
* they directly interfere with DNA replication and it distorts the structure of the double helix

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8
Q

What are some examples of physical mutagens?

A

X-rays, gamma rays, ionizing radiation and UV light

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9
Q

What are induced mutations considered?

A

base modifiers

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10
Q

What is an example of a base analog?

A

5-bromouridine

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11
Q

What are some examples of base modifiers used during induced mutations?

A

nitrous acid and alkylating agents

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12
Q

What does nitrous acid do and how are humans exposed to it?

A
  • it replaces amino groups with keto groups (oxidative deamination)
  • it is formed in our stomach from nitrates that are used in smoked/cured meats
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13
Q

What do alkylating agents do?

A

covalently add ethyl or methyl groups to bases

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14
Q

What base does 5-bromouridine look like and what does it do?

A
  • thymine
  • it tautomerizes from the keto to the enol form at a high rate
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15
Q

What are the two general classes of radiation?

A

ionizing and non-ionizing radiation

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16
Q

List the characteristics of ionizing radiation.

A
  • includes x-rays and gamma rays
  • has short wavelength and high energy
  • can penetrate biological tissues
  • produces free radicals
  • can cause: deletions, oxidized bases, single strand nicks in DNA, crosslinking and double strand breaks in DNA
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17
Q

Wat are the characteristics of non-ionizing radiation?

A
  • has a longer wavelength and lower energy than ionizing radiation
  • its less penetrating but can still cause skin damage
18
Q

What are some examples of non-ionizing radiation sources?

A

sunlight, germicidal lamp and UV LED sample irradiator

19
Q

What can UV Light cause the formation of?

A

a DNA lesion called a thymine dimer

20
Q

Why do thymine dimers occur?

A

adjacent thymine bases become covalently linked, causing errors during DNA Replication

21
Q

What test do we use to tell if an agent is a mutagen?

A

the Ames Test

22
Q

What is the Ames Test?

A

a method foe assessing the mutagenicity of a physical or chemical agent

23
Q

What is the strategy for the Ames Test?

A

start with a salmonella strain that requires histidine to grow
* then expose the salmonella to a suspected mutagen
* if the agent is a mutagen it may cause reversion mutation that restores the ability to synthesize histidine

24
Q

What happens during direct repair?

A

an enzyme recognizes DNA dame=age and directly converts the damaged nucleotides back to the correct form

25
Q

What occurs during excision repair?

A

a damaged base or nucleotide s removed from d=DNA, a segment of DNA in this region is excised and a new DNA strand is synthesized using the complementary strand as a template

26
Q

What occurs during mismatch repair

A

similar process to excision repair but for mismatched normal nucleotides

27
Q

How can damaged bases be removed and repaired?

A

by base excision repair

28
Q

What enzymes are involved in base excision repair?

A

DNA N-glycosylases
* primarily used for non-bulky lesions

29
Q

What is an example of base excision repair?

A

the repairing of uracil in DNA

30
Q

What are the 4 steps for repairing uracil in DNA?

A
  1. uracil DNA glycosylase binds to the DNA that contains a U base
  2. uracil DNA glycosylase then excises the U base yielding an AP site
  3. an AP endonuclease site excises the AP site
  4. DNA polymerase fills in the correct base, then DNA ligase seals the nick
31
Q

Nucleotide excision repair of thymine dimers is used to repair what?

A

bulky lesions by excising a segment of DNA

32
Q

What does Uvr C do?

A

makes 2 cuts on the DNA strand that contains the thymine dimer

33
Q

What does UvrD do?

A

its a helicase that unwinds DNA

34
Q

Defects in nucleotide excision repair cause what condition?

A

xeroderma pigmentosum which is characterized by a severe sensitivity to sunlight and predisposes someone to skin cancer

35
Q

What are the factors that contribute to the fidelity of DNA replication?

A

base insertion, proofreading and mismatch repair

36
Q

What is mismatch repair?

A

when systems correct base pair mismatches

37
Q

Both bases involved in a mismatch are natural, how does the cell know which one is correct?

A

If the mismatch is due to an error in DNA replication, the new strand will contain the incorrect base. New DNA takes time to be methylated.

38
Q

What 3 key proteins are used in the E. coli mismatch repair system?

A

MutS, MutL, and MutH

39
Q

What does MutS protein do in the E. coli mismatch repair system?

A

finds a mismatch in DNA then binds to MutL which is a linker to MutH

40
Q

What does MutH do in the E. coli mismatch repair system?

A

binds to hemi methylated dna and cuts the non-methylated DNA strand

41
Q

What does MutU do in the E. coli mismatch repair system?

A

unwinds the DNA and an exonuclease degrades the new strand until just beyond MutS… this removes the incorrect base

42
Q

What is the role of DNA polymerase in the E. coli mismatch repair system?

A

it fills in the gap and DNA ligase seals the nick

Genetics Unit 4 (4 decks)

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