Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

MCD Cancer > DNA Damage and Repair > Flashcards

DNA Damage and Repair Flashcards

1
Q

why can DNA be easily damaged?

A

their planar, C ring structures with double bonds can easily react with other molecules

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what can damage DNA?

A

o Chemicals
– dietary (40%), medical, lifestyle.
o Radiation
– ionising, solar, cosmic.

  • lifestyle
  • environment
  • occupation
  • medical application
  • endogenous (ROS from mitochondria)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what are the DNA damage forms?

A

o DNA adducts & alkylation – addition of large carcinogenic groups.
o Base dimers & cross-links.
o Base hydroxylation and abasic (base removed) sites.
o Double/single strand breaks.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what happens in phase 1 of metabolism?

A

addition of functional groups via oxidations, reductions, hydrolysis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what mediates phase 1 of metabolism?

A

Mediated mainly by cytochrome p450 enzymes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what happens in phase 2 of metabolism?

A

conjugation of phase 1 functional groups

via glucuronidation, sulphation, glutathione conjugation, methylation, acetylation & amino-acid conjugation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what is the purpose of phase 2 in metabolism?

A

Generates polar (water soluble) metabolites to excrete

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

when can most carcinogens actually become carcinogenic?

A

after phase 1 metabolism

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

how does photo damage of DNA occur?

A

UV can be absorbed by nucleic acids and gain energy. This can induce chemical changes and cause them to react with each other
e.g. form thymidine-dimers (most times its adjacent pyrimidines that react with one another)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what are the types of damage that can occur to DNA strands?

A
  • nicks (breakdown of DNA backbone)
  • gaps (multiple nicks
  • thymine-dimers
  • base pair mismatch
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

3 examples of carcinogens that become carcinogenic post-metabolism

A
  • Polycyclic Aromatic Hydrocarbons (Benzo[a]pyrene)
  • Aflatoxin B1 (liver)
  • 2-naphthylamine (bladder)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

where are Polycyclic Aromatic Hydrocarbons derived from?

A

common environmental pollutants formed from combustion of fossil fuels or tobacco

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what happens in the epoxidation of Benzo[a]pyrene (B[a]p)?

+ve-charged B[a]P adducts onto DNA.

A

o P450 enzymes oxidise the B[a]P (becomes very reactive).
o EH (epoxide hydrolase) removes the toxic oxide. Produces the carcinogen product
o P450 again oxidises the B[a]P which then degrades spontaneously.
o +ve-charged B[a]P then adducts onto DNA.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

where is aflatoxin B1 derived from?

A

Formed by Aspergillus flavus mould and is commonly found in poorly stored grains and peanuts

potent human liver carcinogen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what happens in the epoxidation of aflatoxin B1?

where does it behave as a carcinogen?

A

o P450 oxidises the aflatoxin B1.
o Aflatoxin B1 the adducts to DNA directly using its adjacent guanine N7 positively charged carbon atom.
- becomes a potent liver carcinogen (in Africa and Far-East)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

where is 2-naphthylamine derived from?

A

A past component of dye-stuffs and includes benzidine

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what happens in 2-naphthylamine metabolism?

A

o Cytochrome P1A2 oxidises the amine group.
o Glucuronyl transferase adds a glucuronide group to the amine
- which is the broken by the acidic urine pH.
o The nitrenium ion remaining then causes DNA damage in the bladder.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

how does solar UV radiation cause skin cancer?

A

radiation stimulates formation of pyrimidine (thymine) dimerisation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what are the oxygen free radicals produced by ionising radiation inside cells?

A

free radicals

  • super oxide (O2•)
  • hydroxyl (HO•)

which have unpaired electrons which are now electrophilic and seek out electron- rich DNA

summary: produce electrophilic free radicals that create mutations by strand breaks, apurinic/apyrimidinic sites and base modifications

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

what are the DNA damages that are caused by oxygen free radicals?

A

 Double/single stand breaks.
 Apurinic & apyrimidinic sites – sites where the base is lost whilst the backbone remains.
 Base modifications

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

what are the base modifications caused by free radicals?

A
  • Ring-opening – guanine & adenine.
  • Glycol (unstable products of oxidation) formation – thymine & cytosine.
  • Creation of 8-hydroxyadenine & 8-hydroxyguanine – mutagenic.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

what mainly mediates the repair response to DNA damage?

A

p53 (senses DNA damage and regulates response of the cell to this)

cellular stress management

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

what kind of gene is the gene that encodes p53?

A

tumour suppressor gene

24
Q

examples of cellular/DNA stresses

A
  • mitotic apparatus dysfunction
  • DNA replication stress
  • double strand breaks
  • hypoxia
  • radiation
25
Q

what are the 4 methods of DNA repair?

A 
 Direct reversal of DNA damage 
 Base excision repair 
 Nucleotide excision repair
During- or post-replication repair
- mismatch repair
- recombinational repair
26
Q

what happens in direct reversal of DNA damage for example?

  • splitting of pyrimidine dimers
  • removal of alkyl groups
A

make use of proteins with enzymatic activity on specific reactions

o Photolyase:
- splits cyclobutane pyrimidine dimers (created by solar radiation)

o Methyltransferases (e.g. MGMT) & alkyltransferases:

  • remove alkyl groups
    (e. g. methyls) from the bases.
27
Q

what happens in base excision repair?

A
  • mainly for apurinic & apyrimidinic damage:

o DNA glycosylases remove base without affecting the backbone creating an a[X] base
& apurinic/apyrimidinic endonucleases remove the backbone

o A repair polymerase (e.g. Pol-beta) fills the gap and DNA ligase completes the repair.

28
Q

what happens in nucleotide excision repair?

in what condition is this relevant?

A

Xeroderma pigmentosum
- mainly for bulky DNA adducts:
o Xeroderma pigmentosum proteins (XP proteins) assemble at damage so a stretch of nucleotides are excised.
o A repair polymerase (e.g. Pol-beta) fills the gap and DNA ligase completes the repair.

29
Q

what are the 2 types of repair that happen during or post replication?

A

o Mismatch repair.

o Re-combinational repair.

30
Q

what are the enzymes involved in base excision and what do they do?

A

o DNA-glycosylase – removes the base.
o AP-endonuclease – cuts the backbone.
o DNA polymerase – adds a complimentary base.
o DNA ligase – re-joins the backbone.

need to remove base AND backbone so the DNA glycosylase is important

31
Q

DNA-glycosylase

A

– removes the base.

32
Q

AP-endonuclease

A

– cuts the backbone.

33
Q

what are the enzymes involved in nucleotide excision?

A

o Endonuclease – cuts a large swathe of backbone.
o Helicase – removes 1+ nucleotides.
o DNA polymerase – adds complimentary bases.
o DNA ligase – re-joins the backbone.

34
Q

what are the 2 most common forms of damage to the the DNA?

A

o De-purination.

o Single-strand breaks.

35
Q

how capable is the body of repairing damaged DNA?

A

the body has a much larger capacity than the damage rate per cell
when damage persists for a very long time, there is a greater chance of a mutagenic event

36
Q

what is DNA mismatch repair and when does it occur?

A

during or post translation:

proof reading and identification of bulges in DNA by MSH and cutting out by MLH

37
Q

what are the 3 fates of carcinogen damaged DNA?

A
  1. Repair.
  2. Apoptosis – If the damage is too much.
  3. Incorrect repair –>DNA replication & cell division (fixed mutation) producing aberrant proteins or carcinogenesis at mutated proto-oncogenes or TSGs
38
Q

what are the diseases that involve the Nucleotide Excision Pathway?

A
  • xeroderma pigmentosum
  • trichothiodystrophy
  • Cockayne’s Syndrome
39
Q

what are the methods to test for DNA damage (induced by drugs)?

A
  1. SAR – checking the molecule structurally for groups that could precipitate cancer.
  2. Bacterial gene mutation assay (IN VITRO).
  3. Mammalian cell assay (IN VITRO).
  4. Mammalian assay (IN VIVO).
  5. Investigate mammalian assays.
40
Q

how is the in vitro Ame’s test done?

A

Bacterial Gene Mutation Assay

  • rat liver enzymes (S9) are used to activate (metabolise) the potential carcinogen so that it becomes potentially toxic
  • bacteria are modified so that they do not produce histidine and so require exogenous histidine to grow and survive
  • bacteria mutate with the chemical, they can regain the ability to produce histidine and so will grow even without exogenous histidine
41
Q

what is done with mammalian cells using S9 enzymes?

A

Mammalian cells with the chemical in the presence of liver S9 enzymes are inspected directly for chromosomal damage.

42
Q

what is done in the in vitro micronucleus assay?

A

 Mammalian cells are treated with the chemical and allowed to divide.
 Cytokinesis is blocked using cytochalasin-B
 Bi-nucleate cells are assessed for the presence of micronuclei

cytochalasin has some use in listeria

43
Q

what is stained in the micronucleus assay? what can this determine?

A

The kinetochore proteins are stained to determine if the chemical treatment caused:
o Clastgenicity – chromosomal breakage.
o Aneuploidy – chromosomal loss/gain.

44
Q

how is a double stranded DNA damage repaired?

A
  • Direct joining of the broken ends

- DNA-PK is a nuclear, serine/threonine protein kinase required for repairing DNA double-strand breaks

45
Q

what happens in the in vivo bone marrow micronucleus test?

A

Animals are treated with the chemical and the bone marrow cells or peripheral blood cells are examined for micronuclei.
Erythrocytes can usually remove the nucleus during development but CANNOT remove the small fragments of DNA of which the cell forms a micronucleus around

46
Q

what effect can therapeutic agents have? e.g. in cancer

A

overwhelm cells causing them to undergo cell death by adding bulky adducts and inducing strand breaks etc.

47
Q

what makes DNA vulnerable to electrophiles?

A

DNA are electron rich due to their nitrogen-containing bases

electrophiles will form covalent bonds causing polymerisation

48
Q

why is benzo[a]pyrene dangerous?

A
  • very lipophilic
  • found in most food
  • creates a very reactive carbon species which is very electrophilic
  • this carbon species can adduct to DNA
49
Q

how does 2-naphthylamine become a potent bladder carcinogen?

A

amine group targets the bladder

50
Q

how is p53 regulated? how does it regulate p53?

A

MDM2

suppresses the transcription of p53
therefore needs to unbind to allow p53 to do its ting

51
Q

what does p53 get degraded by?

A

proteasomes

52
Q

how does p53 have a -ve FB effect?

A

activates the transcription of MDM2:

MDM2 levels increases so there is increased p53 degradation by proteasomes

53
Q

how does MDM2 stop its role of p53 suppression i.e. allow p53 to do its role?

A

when MDM2 is phosphorylated its suppressive role of p53 is inhibited

this stabilises p53 and does not become degraded

54
Q

how does p53 allow apoptosis to occur?

A

produces proteins that inhibit Bcl-2 and Bcl-xL (anti-apoptotic)
so they can no longer suppress Bax and Bad proteins (pro-apoptotic)

cytochrome C can be released into the cytoplasm so the apoptosome can be created (using caspases)

55
Q

what is recombinational repair?

A

during or post translational:

takes two damaged DNA and combines them to create a normal DNA strand

MCD Cancer (17 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions