Chapter 2 - Molecular Mechanisms of DNA Damage and Repair Flashcards
What type on damage does ionizing radiation induce?
Single strand breaks
Double strand breaks
Crosslinks
Which strand breaks are most lethal?
Double strand breaks
Double strand breaks are repaired in two ways?
Homologous recombination
Nonhomologous recombination
What is the difference between homologous and nonhomologous recombination?
Homologous recombination happens mainly in S/G2 phases and uses a unbroken template to copy
Nonhomologous recombination happens in G1 and does not use a template.
What letters are pyrimidines?
Thymine and cytosine (single ring group)
What letters are purines?
Guanine and adenine (Double ring group)
Single strand breaks do what biologically?
Not much
Maybe mutations
Double strand breaks do what biologically?
Cell death
Carcinogenesis
Mutations
Which happens more often: Double strand breaks or single strand?
Single strand - 96% of the time
What are spurs and blobs?
The type (size) of track that a particulate or EM took when breaking the DNA… aka the size of the deposition of radiation
The size of the deposition determines the size or number of base pairs affected. AKA Clustered lesions
Spurs are?
3 OH pairs
Blobs are?
12 OH ion pairs
What is a clustered lesion?
The size of the DNA damage in base pairs
What can you use to measure the amount of strand breaks in DNA?
PFGE
- Double strand breaks only
Single-Cell electrophoresis
- can look at individual cells
- Can look at both single strand break and double
DNA damage-induced nuclear foci
- Looks for complexes that repair proteins and quantitate them
What is the difference between intra-strand crosslink and inter-strand crosslink?
Intra-strand crosslink leads to a block in DNA polymerase that is easily overcome
Inter-strand crosslink leads to a block in DNA polymerase that is not easily overcome.
Phases of the cell cycle (mitosis)?
Interphase Prophase Metaphase Anaphase Telophase
What happens in interphase?
DNA duplicates
Chromosomes stay in their domains
What happens in prophase?
Chromosomes condense
Centromeres apparent
Nuclear membrane disappears
What happens in metaphase?
Chromosomes move to center
Spindles form
What happens in anaphase?
Pulling apart chromosomes
What happens in telaphase?
Uncoiling of DNA
Nuclear membranes return
What is a telomere and how do they affect cells?
Telomeres are repeats of TTAGGG. This leaves a long tail of nothingness so that when the cell divides it cleaves the telomere and not the encoding DNA.
However, telomeres only have a certain amount of length and therefore once they are used up the cell quits replicating.
However, stem cells and cancer cells have telomerase which adds more telomere to the ends thus making the cell able to divide indefinitely.
Radiation induced chromosome or chromatid aberrations are looked at in what phase?
Metaphase
Radiation induced chromosome aberrations are noted if radiation is induced when?
Early interphase
Radiation induced chromatid aberrations are noted if radiation is induced when?
Late interphase
What are the three types of lethal aberrations described in this chapter?
Dicentric - Chromosome aberration
Ring - Chromosome aberration
Anaphase bridge - chromatid aberration
Pg: 27
What is an acentric fragment?
Fragments of DNA with no centromere
What two non-lethal aberations are described?
Symmetric translocation - A break in TWO different prereplicated chromosomes
Small interstitial deletion - Two breaks in the same arm of the same chromosome
How can we look for the non-lethal aberrations?
FISH or chromosome painting
How do non-lethal aberrations cause cancer?
Deletion of tumor suppressor genes
Activation of an oncogene
Are interaction between breaks in different chromosomes random?
No— remember they are in domains so they interact within a probability with each other.
Is there a good correlation between killed cells and cells with asymmetric exchange aberrations (dicentric and rings)?
YES so we can use that for estimating cells killed
Is the incidence of most-radiation induced aberrations a function of dose?
YES… linear-quadratic
Can we score aberrations from full body irradiation?
YES with lymphocytes from peripheral blood
What is the lowest dose we can detect from scoring aberration in lymphocytes of the peripheral blood?
0.25 Gray = 25 Rads
Why are dicentric aberrations considered unstable?
They are lethal to the cell and therefore do not pass on the aberrations
Why are translocation aberrations considered stable?
They persist for many years because they are not lethal to the cell. They are passed on to the cells progeny.