Chapter 4 - Radiosensitivity and Cell Age in Mitotic Cycle

Question 1

What is the mitotic or cell cycle time?

Answer 1

Time between divisions

Question 2

Two ways to see the chromatin?

Answer 2

1) You can wash cells with radioactive tritium thymidine to visualize this process…..B-particles that are given off by the DNA create pictures of where the DNA is concentrated
2) Now 5-bromodexoxyuridine which then they wash with fluorochrome- tagged antibodies

Question 3

What is the advantage of 5-bromodexoxyuridine compared to tritium thymidine?

Answer 3

1) No radioactive

2) Shorter time

Question 4

What is the problem with both 5-bromodexoxyuridine and tritium thymidine?

Answer 4

You can only see the chromatine in S- Phase

Question 5

What is the most radiosensitive phase?

Answer 5

M and G2

Question 6

What is the most radioresistant phase?

Answer 6

S

Question 7

Why is S more resistant?

Answer 7

Due to the fact it has two copies of DNA, thus can do Homologous end joining

Question 8

What are the two techniques to synchronize dividing?

Answer 8

Mitotic harvest
- wash the cells and all the ones that are in mitosis and round will wash off. Then you take them and culture them and everything will be in sync.

Drug
Hydroxyurea - kills all cells in S phase and puts a stop at G1. All cells continue to divide until they hit G1. Over time every cell is at G1 and then you release the drug and they are all in sync.

Question 9

Is there a difference in radiosensitivity if the cell is hit with a huge LET particle (alphas)?

Answer 9

NO.. .cause it fucks everythign up that there is no resistence at all.

Question 10

What are molecular checkpoint genes?

Answer 10

They block the cell cycle at G2 after exposed to radiation. They do this to have time to repair DNA before entering M phase. If you lack these then it predisposes you to dying or carcinogensis

Question 11

What is the oxygen enhancement ratio?

Answer 11

It says that the more oxygen present the more effect the radiation will have on the cancer.

Question 12

How does radiotherapy cause synchronization of a tumor population?

Answer 12

It kills all the cells in the sensitive phases M and G2. Then the other cells continue through the cycle more closely synced. There could be a therapeutic gain because of this on the next fraction if timed appropriately