RT Matter Interactions, DNA Damage, DNA Damage Repair Flashcards
annihilation reaction initial event
Photon interacts with a nucleus converting ALL energy into an electron-positron pair
annihilation reaction second event
subsequent positron eventually annihilates with another e- to produce two photons with E=0.511 MeV (annihilation radiation)
When does pair production happen?
High E, high Z
Minimum energy to ionize an atom
10 eV
When does the photoelectric effect happen?
When photon energy is low and close to the binding energy of the orbital e-
In pair production, a 10 MeV photon will transfer what energy to the electron-positron pair?
10 - 1.02 = 8.98 MeV
What is the indirect effect of Compton scattering in water?
The subsequent ionized water molecule will encounter another water molecule and produce a hydroxyl free radical.
Removing histone proteins does what to RT sensitivity
increases sensitivity
6-4 photoproducts are produced by what
UV
BLM protein does what
RecQ helicase works 3>5.
Deficient in Bloom syndrome
What does RPA do?
Coats since stranded DNA regions in HR
What does Ku do?
Fits to DNA ends, it is the initial step of recognition of DNA DSB, followed by activation by DNA-PK
Substrates for ATM
Ku80/90 BRCA1 NBS1 p53 CHK2
Most common type of DNA repair following radiation
BER
Relative to HR, defects in NHEJ are _____ sensitive to RT
More radiosensitive
PARP plays a role in what pathway?
SSB repair, a part of the BER pathway
Clustered DNA damage is more likely to occur with what LET?
High LET
Which repair protein plays a role BOTH in BER and SSBR and confers radiosensitive phenotype when mutated?
X-ray cross complementing factor 1 (XRCC1)
What chromosome aberration follows a linear quadratic function of dose?
dicentric bridges - because they usually need two DSB
Chromosome translocations
What chromosome aberrations are stable?
Symmetrical translocations
Inversions
What chromosome aberration allows you to estimate dose?
Dicentric bridges in lymphocytes a few weeks after exposure
Inversion
Two breaks in the same chromosome, with the straw piece inverted prior to rejoining. Stable.
Rings form in what cell phase
G1
Anaphase bridges occur when
post-replication, G2
What chromosome aberration follows a linear function of dose?
terminal deletions, since they are single hit
Minimum dose that can be detected with dicentric chromosomes?
0.25 Gy
What is a micronuclei?
A small fragment of a chromosome that has broken off
They are created with accentric fragments
What disease has a lot of chromosome aberrations?
Fanconi Anemia - worsens with exposure to DNA cross-linking agents such at Mitomycin-C
