RT Matter Interactions, DNA Damage, DNA Damage Repair

Question 1

annihilation reaction initial event

Answer 1

Photon interacts with a nucleus converting ALL energy into an electron-positron pair

Question 2

annihilation reaction second event

Answer 2

subsequent positron eventually annihilates with another e- to produce two photons with E=0.511 MeV (annihilation radiation)

Question 3

When does pair production happen?

Answer 3

High E, high Z

Question 4

Minimum energy to ionize an atom

Answer 4

10 eV

Question 5

When does the photoelectric effect happen?

Answer 5

When photon energy is low and close to the binding energy of the orbital e-

Question 6

In pair production, a 10 MeV photon will transfer what energy to the electron-positron pair?

Answer 6

10 - 1.02 = 8.98 MeV

Question 7

What is the indirect effect of Compton scattering in water?

Answer 7

The subsequent ionized water molecule will encounter another water molecule and produce a hydroxyl free radical.

Question 8

Removing histone proteins does what to RT sensitivity

Answer 8

increases sensitivity

Question 9

6-4 photoproducts are produced by what

Answer 9

UV

Question 10

BLM protein does what

Answer 10

RecQ helicase works 3>5.

Deficient in Bloom syndrome

Question 11

What does RPA do?

Answer 11

Coats since stranded DNA regions in HR

Question 12

What does Ku do?

Answer 12

Fits to DNA ends, it is the initial step of recognition of DNA DSB, followed by activation by DNA-PK

Question 13

Substrates for ATM

Answer 13

Ku80/90
BRCA1
NBS1
p53
CHK2

Question 14

Most common type of DNA repair following radiation

Answer 14

BER

Question 15

Relative to HR, defects in NHEJ are _____ sensitive to RT

Answer 15

More radiosensitive

Question 16

PARP plays a role in what pathway?

Answer 16

SSB repair, a part of the BER pathway

Question 17

Clustered DNA damage is more likely to occur with what LET?

Answer 17

High LET

Question 18

Which repair protein plays a role BOTH in BER and SSBR and confers radiosensitive phenotype when mutated?

Answer 18

X-ray cross complementing factor 1 (XRCC1)

Question 19

What chromosome aberration follows a linear quadratic function of dose?

Answer 19

dicentric bridges - because they usually need two DSB

Chromosome translocations

Question 20

What chromosome aberrations are stable?

Answer 20

Symmetrical translocations

Inversions

Question 21

What chromosome aberration allows you to estimate dose?

Answer 21

Dicentric bridges in lymphocytes a few weeks after exposure

Question 22

Inversion

Answer 22

Two breaks in the same chromosome, with the straw piece inverted prior to rejoining. Stable.

Question 23

Rings form in what cell phase

Answer 23

G1

Question 24

Anaphase bridges occur when

Answer 24

post-replication, G2

Question 25

What chromosome aberration follows a linear function of dose?

Answer 25

terminal deletions, since they are single hit

Question 26

Minimum dose that can be detected with dicentric chromosomes?

Answer 26

0.25 Gy

Question 27

What is a micronuclei?

Answer 27

A small fragment of a chromosome that has broken off

They are created with accentric fragments

Question 28

What disease has a lot of chromosome aberrations?

Answer 28

Fanconi Anemia - worsens with exposure to DNA cross-linking agents such at Mitomycin-C