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DNA damage Flashcards

(71 cards)

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1
Q

What are the two classifications of DNA damage?

A

Spontaneous

Environmental

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2
Q

What is DNA damage?

A

Modifications in the molecular structure of the genetic material

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3
Q

Spontaneous DNA damage is a result of what?

A

Normal metabolism

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4
Q

Environmental DNA damage is a result of what?

A

Environmental factors (mutagens and carcinogens) found in food, water etc

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5
Q

What is a carcinogen?

A

Induces unregulated growth

Epithelium in origin

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6
Q

What is a mutagen ?

A

Induces change in genetic material

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7
Q

What are the 4 classes of spontaneous DNA damage?

A

Tautomeric shifts
Deamination
Depurination/depyramidination
Oxidative damage

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8
Q

What is a tautomeric shift?

A

When any of the 4 bases undergo spontaneous rearrangement in bonding to form a tautomer

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9
Q

The tautomer of amino is ?

A

Imino

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10
Q

What 2 bases form imino forms of tautomers usually?

A

Cytosine and adenine

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11
Q

What is the tautomeric form of a Keto called?

A

Enol

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12
Q

What bases form Enol tautomer?

A

Thymine and guanine

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13
Q

What is deamination?

A

When the entire amine (nh2) group is removed

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14
Q

What reaction is deamination?

A

Hydrolytic

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15
Q

What factors are deamination dependent upon?

A

Temperature and ph

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16
Q 
List the deaminated forms of the following bases.... 
cytosine 
Adenine 
Guanine 
5-methyl cytosine
A

Uracil
Hypoxanthine
Xanthine
Thymine

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17
Q

What is depurination/depyrimidination?

A

When the entire base is lost

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18
Q

Under what conditions do depurination / depyrimidination thrive?

A

Acidic ph

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19
Q

What reaction occurs during depurination/ depyrimidination

A

Hydrolysis of the N - glycosidic bond via protonation of water

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20
Q

What reaction aids depurination/ depyrimidination?

A

Protonation of water

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21
Q

What is produced during depurination/ depyrimidination?

A

A basic sites

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22
Q

Are purines or pyrimidines lost faster and by what factor?

A

Purines

20x faster

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23
Q

What base is depurinated faster under ACIDIC conditions?

A

Guanine 1.5 times faster

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24
Q

Oxidative damage is a result of what?

A

Normal aerobic metabolism

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25
What does oxidative damage form ?
Reactive oxygen species (ROS)
26
Give 4 examples of ROS
Singlet oxygen Organic peroxides (hydrogen peroxide) Superoxide anion radicals Fenton reaction generated hydroxyl radicals
27
What is the most frequent type of DNA damage?
Oxidative damage
28
Why is oxidative damage the most common type of DNA damage?
Continuous cellular production of ROS
29
What is the downstream effect of ROS?
Convert target molecules into radicals when trying to get a full configuration of electrons and so generate chain reaction until 2 radicals pair
30
In addition to normal metabolism, under what other mechanisms are ROS generated?
Long wavelength IV | IR
31
What mechanism has cells developed in order to protect against ROS ?
Scavengers
32
What are the two classifications of environmental DNA damage ?
Physical agents | Chemical agents
33
List the physical agents that cause environmental DNA damage..
``` UV Ionising radiation (IR) ```
34
What are the two main UV light induces DNA photo products?
Cyclobutane pyrimidine dimers | Pyrimidine 6-4 pyrimidone photo products
35
What are CPDs
Bond formation between adjacent pyrimidine on the SAME DNA strand due to influx of energy when bases absorb uv light
36
What is the order of frequency of CPDs?
T-T> T-C/C-T > C-C
37
What does a CPD cause ?
A kink in the DNA strand when the two pyrimidines are pulled in closer than normal
38
What bond is formed when cpd are formed?
DOUBLE covalent bond
39
What are 6-4 PPs
pyrimidine dimer when a SINGLE covalent bond is formed between the 6 position of one pyrimidine and the 4 position of the adjacent pyrimidine on the 3' side
40
What is the order of frequency of the pyrimidine dimer formation
T-C > C-C > T-T > C-T
41
What type of pyrimidine dimer he the greatest distortion? List the values?
44 degree bend vs 7-9 degree bend (64PP vs CPD)
42
What is unique about IR damage?
Causes damage to all cellular components not only DNA
43
What is the majority of IR damage due to? Give a value
80% - production of ROS due to water radiolysis
44
80% of IR damage is due to the production of ROS, via what mechanism are these ROS formed ?
Radiolysis of water
45
65% of IR Damage is due to what?
Hydroxyl radical
46
IR had the same consequence as oxidative damage ... what is this consequence?
Base dimerisation | DNA protein crosslinks
47
Why is IR damage so severe ?
Capable of depositing numerous ROS in the same DNA locale and therefore producing multiple closely spaced damages on BOTH strands of DNA
48
Multiple damaged sites are formed during IR damage, what does this lead to ?
Ds DNA breaks | Clustered base damage
49
What beneficial aspects do chemical agents, that also cause DNA damage, possess?
Chemotherapeutics
50
What do alkylating agents do?
Add alkyl groups to electronegative groups
51
What are alkylating agents structure like?
Electrophilic | High affinity for nucleophilic centres
52
What are the two classes of alkylating agents?
Mono functional and bifunctional (single/2 reactive groups that react with single site/2 sites on DNA)
53
How to alkylating agents act as chemotherapeutics?
Cross link guanine bases in DNA double helix and so strands can't recoil a process necessary for replication and so division
54
What is a second mechanism by which alkylating agents cause DNA damage?
Cross linking agents - form cross bridges (bonds between atoms) in DNA
55
Cross bridges are formed by what type of alkylating agent?
Bifunctional - 2 DNA binding sites
56
How does cross linking agents acts as chemotherapeutics ?
Cross linking prevents strand separation and so prevents synthesis and transcription
57
Cross linking agents are used in what 2 chemotherapeutic drugs?
Carboplatin | Cisplatin
58
What are psoralens?
Photosensitising furocaumarins that upon photoreactivation with long wavelength UV form covalent adducts to pyrimidine bases on DNA
59
What is the result of psoralens?
DNA crosslinks Distortion Unwinding of DNA
60
Psoralens can cause what?
Phytophotodermititis (found in fruit and veg)
61
What is the conformation of psoralens?
Planar tricyclics configuration
62
How does the structure of psoralens aid their function?
Planar tricyclic allows it to slip between base pairs on DNA
63
How do electrophilic reactant metabolites become reactive ?
Undergo metabolic conversion in the liver by e.g cytochrome p-450 system
64
How is the electrophilic metabolite AAF carcinogenic?
Reacts with c8 and n2 positions of nuclei acids to form DNA adducts
65
What does AAF stand for?
N-2-acetyl-2-amino fluorescence
66
What is benzo [a] Pyrene ?
Polycyclic aromatic hydrocarbon
67
What is the most carcinogenic compound?
Benzo[a] Pyrene
68
How are benzo[a] Pyrenes toxic ?
Metabolised by liver enzymes to excretable products and potent epoxides that covalently bind to amino group of guanine
69
Aflatoxinsare an example of what
Mycotoxin
70
What is the most reactive form of aflatoxin?
B1
71
What is the action of B1 aflatoxin
Epixide form (after metabolism in the liver) attacks bases (especially guanine) to form DNA adducts

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