RBP L2 - DNA Damage by Radiation Flashcards
DNA consists of a backbone of alternating sugar (deoxyribose) and phosphate molecules. One of the four organic bases is attached to each sugar molecule.
True
DNA is the principal target for Biological Effect
True
The nucleotide in DNA has three parts: a phosphate group, a five-carbon sugar called deoxyribose, and one of four nitrogenous bases – adenine (A), guanine (G), cytosine (C), or thymine (T).
True
What holds the two strands of DNA together?
Hydrogen bonding between the bases
What is D0?
D0 = 37% cell survival
What is D0 for mammalian cells? How much base, SSB and DSBs does this equivilate to?
1-2Gy, 1k base and 1k SSB, 40 DSB
Compare SSB and DSB in terms of damage/repair
SSB are of little biological consequence. They can be repaired easily using the opposite strand as a template. DSB, if breaks are far then can be repaired individually. If directly opposite, may lead to chromatin snapping
A break in one strand is of little significance because it is repaired readily, using the opposite strand as a template.
True
Breaks in both strands, if well separated, are repaired as independent breaks.
True
If breaks occur in both strands and are directly opposite or separated by only a few base pairs, this may lead to a double-strand break in which the chromatin snaps in two pieces.
True
How much energy does a spur vs. blob contain?
Spur has 100eV, Blob has 100-500eV
How many ion pairs dos a spur vs. blob contain?
Spur has 3, Blob has 12
How big (diameter) is a spur vs blob?
Spur 4nm, Blob 7nm
What is the diameter of DNA? Why is this important?
2nm, important because since spurs are 4nm and blob are 7nm, they can break the DNA strand
Are spurs or blobs more common in x-rays?
SPURS - 95%
What are some possibilities once DNA is damaged (in terms of repair mechanism)
They can just repair normally, so nothing wrong is seen. They may fail to rejoin and deletion happens. OR, broken ends join together and is seen as a mutation
The repair mechanisms used for Base repair can be used for DSB repair
FALSE!!!
What are APE1 and DNA glycosylase?
They are ‘removers’ of the base that is wrong “U”
What molecule comes and gives the right base for base-excision repair?
DNA polymerase
What is Nucleotide Excision Repair?
It removes bulky adducts in DNA such as pyrimidine dimers
What are the two pathways for NER? What is the difference between the two?
GG-NER and TC-NER. GG repairs everywhere, TC only repairs at DNA w/ ACTIVELY TRANSCRIBED GENES
The mechanism of GG-NER and TC-NER differs only in the detection of the lesion; the remainder of the pathway used to repair the damage is the same for both.
True
What does Nucleotide Excision Repair consist of (in general terms)
Find the damage, cut out the damage along with its surroundings, remove it, repair it, glue it
Describe DSB Repair in terms of cell cycle
In G1, NHEJ occurs, in S and G2, HRR occurs
Non-homologous End Joining and Homologous Recombination Repair
