1. Which of the following statements is false?

a. Autoradiography (a cell-labelling technique) can be used to determine the lengths of the various phases of the cell cycle.

b. Autoradiography has been used to show that cells synthesize DNA only during the S phase.

c. Autoradiography can be performed using tritiated thymidine or bromodeoxyuridine.

d. All proliferating mammalian cells have cell cycle phases of equal length irrespective of their type.

2. Which of the following statements is false?

a. By "synchronously dividing cell culture" is meant a population of cells in which all cells are at the same phase of the cell cycle simultaneously.

b. Synchronously dividing cell curves are used to study how the radiosensitivity of the cell varies with the age of the cell, i.e. with the position of the cell in the cell cycle.

c. The mitotic harvest technique consists in producing a synchronously dividing cell culture by killing all the cells that are at mitosis.

d. The use of a drug such as hydroxyurea produces a synchronously dividing cell culture by killing all cells that are in the S phase and by imposing a block at the end of the G₁ phase of the cell cycle.

3. Irradiation with x-rays of HeLa and Chinese hamster cells harvested at mitosis has shown that the cells are most sensitive when they are:

a. in the M phase of the cell cycle.

b. in the G₁ phase of the cell cycle.

c. in the G₂ phase of the cell cycle.

d. in the S phase of the cell cycle.

4. Which of the following statements is false?

a. Cells in the S phase are radioresistant.

b. When the G₁ has an appreciable length, it has been shown to be resistant in its early part and sensitive in its late part.

c. Cells in the G₂ phase are resistant.

d. The G₂ phase is almost as sensitive as the M phase.

5. Mitotic cells under conditions of hypoxia are as radiosensitive as:

a. mitotic cells that are aerated.

b. cells in the late S phase.

c. cells in the G₁ phase.

d. cells in the early S phase.

6. Which of the following statements is false?

a. "Molecular checkpoint genes" are genes that control the cell-cycle progression.

b. One particular molecular checkpoint gene is responsible for halting the cell at G₂ when a small dose has been delivered to the cell. The purpose of halting the cell cycle at G₂ is to check for chromosome damage and repair it before the cell attempts to divide. This results in a pilling up of cells in G₂.

c. Cells containing mutant G₂-halting genes are more sensitive to ionizing radiation than the wild type, as they proceed directly to mitosis without previously repairing chromosome damage caused by the radiation.

d. The inverse dose-rate effect, according which cells become more sensitive to radiation-induced cell killing as the dose rate is increased, is due to the G₂ pilling up mentioned in answer b.

7. The variation of radiosensitivity as a function of cell age has been found to be qualitatively similar for x-rays and neutrons but the variation of sensitivity is smaller in the case of neutrons.

a. True.

b. False.

8. The variation of cell radiosensitivity with cell age might be due to:

a. changes in the amount or form of the DNA and/or changes in the level of naturally occuring sulfhydryl compounds in the cell.

b. changes in the oxygen enhancement ratio.

c. the activation of different members of the cyclin-dependent kinase family.

9. The variation of cell radiosensitivity with cell age is important to radiotherapy because:

a. the first dose of radiation synchronizes the cell population.

b. sensitization does not occur in rapidly dividing cells.

c. sensitization does not differentiate between cancer cells and normal cells.

d. the first dose of radiation kills all cells which are at the S phase of the cell cycle.

10. The oxygen enhancement ratio shows a significant variation during the cell cycle.

a. True.

b. False.