8. The E3 ubiquitin ligase complex SCF can target its substrates for destruction

Question

8. The E3 ubiquitin ligase complex SCF can target its substrates for destruction when

a.SCF substrates are phosphorylated

b.SCF substrates are de-phosphorylated

c.SCF is bound to its co-activating factor

d.SCF component Skp1 is phosphorylated

e. SCF component Skp1 is de-phosphorylated

11. How does the retinoblastoma (Rb) protein function in the cell cycle?

A) Inhibits the myc, jun, and fos transcription factors

B) Activates the MAPK pathway

C) Inhibits the MAPK pathway

D) Activates the cyclin dependent kinase inhibitor INK family

E) Inhibits transcription of cell cycle progression genes

F) Prevents Ras activation

12. Which of the following is TRUE?

A. Active CyclinE/CDK levels increase because Cyclin E/CDK activates the APC/C,                                    

   which results in a downregulation of CyclinE/CDK inhibitors

B. Active CyclinE/CDK levels increase because Cyclin E/CDK phosphorylates                                                

                  CyclinE/CDK inhibitors, which targets them for destruction

C. Active Cyclin E/CDK levels increase due to the fact that Cyclin E/CDK can phosphorylate                                 CDC25, a phosphatase that removes inhibitory phosphates from CyclinE/CDK complex

D. Active Cyclin E/CDK levels increase in response to destruction of geminin, a protein that                               sequesters Cdt1

14. Activation of Cyclin B / CDK

A) phosphorylates and activates stabilizing Microtubule Associated Proteins

B) phosphorylates and promotes activity of Wee1 family kinases

C) phosphorylates nuclear lamins to weaken the nuclear envelope

D) phosphorylates and activates Rb (retinoblastoma) protein

E) phosphorylates and activates DNA replication enzymes

15. Chromosome congression during mitosis DOES NOT require

a. GTP hydrolysis

b. Ndc80 complexes linking kinetochores to microtubules

c. actin treadmilling

d. microtubule dynamic instability

18. Activation of the APC/C E3 ligase results in the following:

a. proteolytic degradation of the mitotic CDKs

b. proteolytic degradation of securin, which promotes cohesin removal from sister chromatids

c. activation of Cdc25

d. eviction of the Pre-RCs from origins of replication

22. Cells expressing a mutant version of the Spindle Assembly Checkpoint protein Mad2 in which it is constitutively in an “open” conformation would likely:

a. enter anaphase prematurely

b. enter M phase prematurely

c. arrest at the Metaphase to Anaphase transition

d. arrest in late G2

e. arrest in G1, prior to S phase

Explanation / Answer

8. a.SCF substrates are phosphorylated.

11. E) Inhibits transcription of cell cycle progression genes.

12. C. Active Cyclin E/CDK levels increase due to the fact that Cyclin E/CDK can phosphorylate CDC25, a phosphatase that removes inhibitory phosphates from CyclinE/CDK complex.

14. C) phosphorylates nuclear lamins to weaken the nuclear envelope.

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