Cyclins and NE Case Study

1. What stage of the cell cycle is associated with DNA replication?

2. Predict how the staining intensity of propidium iodide would change the with the cell cycle.

3. Cell cycle and mitosis
4. Explain how reducing the levels of cyclin mRNA would affect the activity of a Cdk.

5. dTTP acts as an allosteric inhibitor of the enzyme required to synthesize cytosine. Explain why inhibiting this enzyme would result in blocking progression of the cell through the cell cycle.

6. Research/review the function of the nuclear localization sequence.

7. What is luciferase? Suggest a reason the researchers included GL3 in their experiments?

8. Does the absence of a dark band on the immunoblot mean that there is no cyclin protein in the cell?

9. How much time is required before NEB in HeLa cells?

10. Use the data presented in Figure 13.2.1c to determine which cyclin (or cyclins) is involved in regulating NEB.

11. What is the centrosome? Look at the image in Figure 13.2.3 to find when the centrosomes separate.

12. Approximately how long does it take the centrosomes in the GL3 knockdown cell to orient themselves at opposite ends of the nucleus?

13. What is the interval of time between the accumulation of cyclin B1 in the nucleus and NEB for the GL3 knockdown (control) cells? CyclinA2 knockdown cells?

Cyclins and NE Case Study Answer 

2. Predict how the staining intensity of propidium iodide would change the with the cell cycle.

• Since propidium binds to DNA, during the G₁ phase, it would be of ‘normal’ intensity. Once it undergoes the S phase, however, the staining will darken considerably (twice the normal intensity) as the DNA is duplicated, doubling the number of DNA molecules present. This level of intensity will remain until Mitosis, specifically during the Anaphase/Telophase. During this stage, the condensed DNA will split into two, and the propidium iodide reverting to its ‘normal intensity’.