DNA Damage Flashcards
(30 cards)
DNA can be damaged in a _______ of ways?
variety
DNA damage is NOT the same as a ________.
mutation
DNA damage is a ________ to the DNA
chemical alteration
A mutation is a change in a __________.
base pair
Give an example of DNA damage and a DNA mutation.
G-C altered to methyl-G-C is damage.
G-C altered to any other base pair is a mutation.
________ DNA can lead to mutations.
Unpaired
What are three types of DNA damage?
- alkylation of bases
- UV induced cross linking
- Damage by high energy radiation(ionizing radiation)
When does alkylation occur?
When electrophiles bind to centers of negative charge and add a carbon containing group (alkyl group)
What specific sites are especially vulnerable targets for electrophilic attack in DNA?
Phosphate groups
N7 of guanine
N3 of adenine
WHich attack on one of the three specific sites is harmless and why?
The alkylation of N7 of guanine is harmless because it does not change the base pairing properties of guanine.
WHat happens when N3 of adenine is alkylated?
3-methyl adenine (3mA) is created that causes the molecule not to be able to base pair properly with any other base.
What is an example of a noncoding base?
3mA
How is 3mA lethal to a cell?
DNA polymerase will not recognize any base pair involving 3mA since it is a noncoding base and therefor stalls at the 3mA damage.
CAn the stalling at the 3mA be corrected?
The stalling of the replication can be resumed without repairing the damage but this tends to lead to erroneous replication that leads to mutations.
What happens when the O6 of guanine is attacked by an alkylating agent?
This is a very rare event, however when the attack does occur it is extremely mutagenic! The alkylating product can base pair with Thymidine rather than cytosine.
What reagent can cause the O6 of guanine to be alkylated?
Ethylmethane sulfonate
What are common electrophiles and damage DNA by alkylating it?
carcinogens
How does UV radiation damage DNA?
UV induces the formation of pyrimidine dimers by cross-linking pyrimidines on the same DNA strand. The dimers block DNA replication.
WHat is a common dimer formed by UV radiation?
thymidine dimers
The electromagnetic radiation from the sun contains wavelengths in the UV part of the spectrum. How does this affect humans?
HUmans are exposed to the sun daily and thus the UV radiation. UV damages in the DNA cells of our skin can lead to mutations that sometimes cause the cells to lose control over their division.
What a thymidine dimer forms what ability of the DNA is impaired?
The ability of the 2 T to pair with the A
UV energy interacts directly with DNA to promote what?
dimerization
What absorbs most of the UV light on Earth?
Ozone layer
DNA damage from ionizing radiation is caused from what?
high energy X-rays and Gamma radiation
