RPB L6 - Cell Cycle & Radiosensitivity

Question 1

M, S, G0, G1, G2; Which stages are radioresistant and which are radioresistive?

Answer 1

S, G0 and G1 are resistive. M, G2 are sensitive

Question 2

Is S or G1 more radioresistive?

Answer 2

S!

Question 3

How is the cell cycle regulated?

Answer 3

By CDK and cyclin. Cyclin activates CDK, which phosphorylates proteins required for cell cycle/DNA replication

Question 4

What is cyclin and CDkinase?

Answer 4

cyclin is a protein, CDK is an enzyme. Think of it as protein toa ctivate then enzyme to go and do stuff

Question 5

What is p53 and Rb?

Answer 5

They are checkpoint genes, between G1 and S

Question 6

When are cells most radioresistive in the S phase?

Answer 6

at the END of S phase!

Question 7

If a survival curve had a large/broad shoulder, what does this mean?

Answer 7

It means that they are more radioresistive; for example, S phase would have a large shoulder

Question 8

Would M phase have a steep line or a curved shoulder?

Answer 8

STEEP- it is radiosensitive

Question 9

Why are cells more resistant in the latter part of S phase?

Answer 9

increased resistance is thought to be caused by homologous recombination repair between sister chromatids that is more likely to occur after the DNA has replicated

Question 10

If G1 phase has an appreciable length, a resistant period is evident early in G1, followed by a sensitive period toward the end of G1.

Answer 10

True! Read this carefully!

Question 11

What are the different types of base mutations?

Answer 11

Point mutation, insertion, deletion

Question 12

Cells in which the checkpoint gene is inactivated are much more sensitive to killing by γ-rays or ultraviolet light.

Answer 12

True- They don’t have ‘police cell’ to protect them

Question 13

Are x-rays or neutrons more ionising?

Answer 13

neutrons

Question 14

What is “reassortment”?

Answer 14

Cells cycle through the cell phases, sometimes cells may be in the sensitiv phase, next cycle they go into the non-sensitive phase; this is the basis for RT

Question 15

What are the 4 R’s of radiobiology?

Answer 15

Repair, reassortment, Reoxygenate, Repopulate

Question 16

SSB’s that are not repaired before mitosis is called?

Answer 16

Mitotitc death

Question 17

Cell death from SSB have a linear dose-response curve

Answer 17

true; higher dose = more SSD

Question 18

Reassortment: What is the optimal time to wait after first irradiation to do the second one? (cells in sensitive state)

Answer 18

6 hours. 2-4 they still chillin

Question 19

Does reassortment make the survival curve go up or down?

Answer 19

DOWN; reassort = less cells survive

Question 20

Describe repopulation

Answer 20

Cells enter the resistive phase; they proliferate

Question 21

Oxygen effect makes cells radiosensitive for high and low LET

Answer 21

FALSE - only for low LET!!!!

Question 22

Explain the oxygen effect

Answer 22

Oxygen reacts/binds to free radical. They go to hit DNA. Oxygen blocks the repairers

Question 23

What is Bergonie’s law?

Answer 23

Tissues appear to be more “radiosensitive” if their cells are less-well differentiated, have greater proliferative capacity & divide more rapidly.

BerGONE!

Question 24

Is DSB or SSB more important in RT?

Answer 24

DSB because SSB are more easily repaired

Question 25

What are the 4 R’s in Radiobiology?

Answer 25

Repair, reassort, reoxygenate, repopulate