Biol 309 Test Question Bank Cell Cycle

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Biol 309 Test Question Bank Cell Cycle

    Biol 309 Test Question Bank Cell Cycle

Multiple Choice

1. The role of „cyclin‟ in the regulation of the cell cycle would be best compared to:

     A. a digital watch that produces a precisely timed signal every few microseconds.

     B. a row of dominoes, that all fall sequentially after the first one is flipped.

     C. a light switch that alternates between on and off states.

     D. the accumulation of sand in an hourglass.

2. Which one of the following statements best describes the mechanism by which the "cell cycle

    control system" regulates events of the cell cycle? ++ A. Ca and cAMP are leased into the nucleus at particular times.

     B. Protein activity is regulated through phosphorylation and dephosphorylation.

     C. Specific hormones signal when its time to move to each stage of the cell cycle.

     D. Changes in membrane potential signal progress of the cell cycle.

3. A cell cycle "checkpoint" would be best described as:

     A. a site in the cytoplasm where proteins are inspected for mutations.

     B. either G1, S, G2, prophase, metaphase, anaphase or telophase.

     C. specific stages where further progress of the cell cycle can be halted.

     D. any step where the cell cycle is blocked by a mutated protein.

    4. The figure to the right shows the changes in the level of a cyclin and activity of cyclin-Cdk during the cell cycle. Note how the level of cyclin increases slowly & steadily, whereas the activity of the cyclin-Cdk appears quite suddenly. How would we best explain the rapid activation of cyclin-Cdk?

     A. Cyclin-Cdk gene expression leads to rapid protein synthesis.

     B. All cyclin-Cdk is activated when it exists the nucleus.

     C. Ubiquination leads to proteolytic activation of the cyclin-Cdk.

     D. A positive feedback loop causes its rapid activation.

    5. Which of the following statements correctly describes p53?

     A. It is a membrane receptor that binds to a cell growth hormone.

     B. Cell division stops until p53 binds to DNA and repairs the damage.

     C. p53 is an example of an oncogene, and its expression causes uncontrolled cell division.

     D. activation of p53 leads to inhibition of the S-phase cyclin-CDK complex.

    6. All of the following statements correctly describe M-Cdk, EXCEPT:

     A. M-Cdk causes the cell to enter S phase and begin DNA replication.

     B. M-Cdk has two subunits, a protein kinase and a cyclin-type protein.

     C. M-Cdk only becomes active during M-phase.

     D. M-Cdk triggers many events by phosphorylating other proteins.

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7. The figure to the right shows that injection of M-phase

    cytoplasm into an oocyte triggers the cell to enter mitosis. What would be the expected effect on cell division if

    cytoplasm from a G2-phase cell were injected into an M-

    phase cell?

     A. DNA replication would begin again.

     B. activation of all cyclin-CDK complex in the cell.

     C. it should have essentially no effect.

     D. mitosis will immediately stop.

8. Which one of the following statements best describes the relationship between tumor suppressor

    proteins (TSP) and cancer?

     A. TSPs usually become mutated as a late event during cancer development.

     B. When activated, TSPs will cause uncontrolled cell division.

     C. Mutation of a TSP predisposes a cell to formation of oncogenes.

     D. Mutation to a TSP will cause a cell to undergo apoptosis.

9. Certain cell surface molecules of bacteria can trigger cells of the immune system to abnormally

    begin to divide, sometimes leading to severe symptoms. This type of molecule would be best

    described as a:

     A. growth factor C. mitogen

     B. survival signal D. hormone

10. Apoptosis involves all of the following events, EXCEPT:

     A. phagocytosis by macrophages.

     B. fragmentation of DNA.

     C. triggering of inflammation.

     D. formation of small membrane-bound vesicles.

11. Which of these types of proteins are most responsible for assuring that cells do not replicate if

    there is DNA damage?

     A. cyclins C. protooncogenes proteins

     B. tumor suppressor proteins D. inactivating phosphatases

    12. Each of the following events is likely to trigger cell apoptosis, EXCEPT:

     A. release of mitochondrial proteins into the cytosol.

     B. binding of Fas/FasL proteins on the cell surface.

     C. mutations that inhibit the activity of P53.

     D. unrepairable DNA damage.

True or False

    1. Many tumor suppressor genes are involved in the detection and repair of DNA damage.

    2. Protein kinases are proteins that add phosphates to other proteins.

3. Cyclins are kinases.

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4. Cyclins are targeted for destruction through ubiquination.

    5. A gene encoding a DNA repair enzyme would be an example of a protooncogene.

    6. S-phase Cdk activates DNA synthesis at replication origins, and its immediate destruction is what prevents subsequent reactivation.

    7. Activation of caspase-type proteases is the first event triggering mitosis.

    8. Necrosis is the end-result of the systematic self-destruction of a cell.

    9. Many genes involved in check-point control of the cell-cycle would be classified as tumor-suppressor genes.

    10. Once mitosis begins, checkpoint control does not occur until the cell reenters G1.

    11. Proteases in the caspase family are responsible for the destruction of cyclin-Cdk.

    12. Different cyclin-Cdks are responsible for triggering different stages of the cell cycle.

. Mitogens are substances that trigger apoptosis. 13


1. Stage of cell cycle Cellular event or process

    __M A. cell metabolism prepares for mitosis

    __S B. ribosome and organelles increasing in number

    0 C. cell is not actively dividing __G

    __G1 D. histone synthesis is in high gear

    __G2 E. microtubule organizing center has been replicated

2. Protein function

    __ cyclin A. phosphorylates target proteins

    __ cdk B. remove a phosphate from cyclin-Cdk

    __ cyclin-cdk complex C. triggers destruction of cyclin-Cdk

    __ activating phosphatase D. is the kinase in activated cyclin-Cdk

     E. ubiquination leads to its proteolysis

    Fill-in etc

    1. The detection of _________________ causes activation of p53. When activated, p53 triggers transcription of the protein called ___________, which itself acts to inhibit _______________.

    2. Uncontrolled rupturing of a cell is called ______________________, whereas controlled destruction of the cell into membrane-bound fragments is called ___________________________. The latter process is mediated by activation of a cascade of proteases called ___________________.

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    3. _________________ are proteins that accumulate during the cell cycle and bind to proteins called ________________, which possess kinase activity when activated.

    4. Among extracellular signals that influence cell proliferation and programmed cell death are _________________ which actively stimulate cell division. In contrast, B7 which binds to CD28 on the surface of T-cells and prevents them from undergoing apoptosis would be classified as a __________________. Growth and differentiation of cells are stimulated by molecules called __________________.

    5. Among the triggers that lead to activation of p53 is damage to _________. Upon activation, p53 acts as a _________________________, stimulating expression of the gene for the protein ______________. This protein then stops cell division by binding to and inactivating __________.

    6. There are two pathways leading that can trigger apoptosis. The _______________ pathway is triggered by internal signaling events and results in the release of ___________________ from the mitochondria. The __________________ pathway is triggered by external signaling molecules. In either case, the effectors of cellular destruction are members of the ___________________ family of proteins.

    7. Explain the concept of a “checkpoint” in the cell cycle control system. Are the genes that code of checkpoints most likely to be protooncogenes or tumor suppressor genes? Explain.

8. In the figure to the right:

    Identify the proteins labeled as

    A. ___________________

    B. ___________________

    C. ___________________

    D. ___________________

    E. ___________________

Explain what is happening in the processes labeled as:

    X --

    Y --

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9. In the figure to the right:

    Identify the proteins labeled as

    A. ___________________

    B. ___________________

    C. ___________________

    What event has occurred in the step labeled as „X‟?

    If this is M-CdK, when during the cell cycle does „X‟ occur (be precise)?

10. Clam eggs were fertilized and allowed to undergo several rounds of a synchronous cell division in 35 labeled methionine. At different times during a replication cycle, some of the the presence of S

    eggs were collected and homogenized, subjected to SDS-PAGE, and labeled peptides then identified by autoradiography. The figure below shows the results for part of the gel. Each lane represents a sample collected sequentially during the cell cycle.

Explain your answers to the following questions. 35A. Why are proteins labeled with S labeled methionine in this experiment?

    B. How would the results appear if the cells were not dividing synchronously? C. If the gel had instead been stained for total protein, what would you expect to see? D. What is happening to peptides A and B, as indicated by the increase in intensity of their bands

    during the cell cycle? Why does the intensity of the bands suddenly diminish? E. Are peptides A and B most likely cyclins, Cdks, or cyclin-Cdks. Which one is most likely coupled

    to the triggering of S-phase? … to M-phase?

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11. In a recent study of the control of cell division (Groth et al. 2008. Science 318:1928-1931), the

    researchers used synchronously dividing cultured human cells. Cells were synchronized using a

    technique called a double-thymidine-block, which is performed by incubating dividing cells twice in

    the presence of a high concentration of thymidine (phosphate-lacking nucleotide), with an intervening incubation without thymidine. During the initial thymidine treatment, cells in mid-S-phase immediately arrest and other cells will stop dividing when they reach the G1/S boundary. Incubation in medium lacking thymidine is then allowed long enough for the cells to pass through S-phase before a second thymidine treatment arrests all cells at the G1/S boundary.

    A. Explain why two sequential treatments with thymidine are necessary to synchronize all of the


    (cont. next page)

    Placing the cells in medium lacking thymidine releases the „block‟ and cells begin to divide synchronously. At different time points after releasing the block, FACS (fluorescence activated cell sorting) can be used to count cells and measure their DNA content. This was done for synchronously and asynchronously dividing cells. Results for 3 samples are shown in Figure 1, in which number of cells is plotted on the y-axis and cell DNA content is on the x-axis.

    B. Which graph presents the expected results for asynchronously

    dividing cells, for cells in S phase, and for cells predominantly

    in G2? Explain your answers.

    C. Why does cell DNA content in samples B and C occur predominantly in 2 values?

    Using this system Groth et al. investigated the role of the protein Asf1 in the cell cycle. In one study they repressed Asf1 expression via RNA interference by treating the cells with siAsf1, a small RNA that targets Asf1 mRNA. As a control, cells were treated with siGFP, which would repress expression of the GFP gene. The results for asynchronous cells are shown in Figure 2.

    D. Why is treating some cells with siGFP (even through the GFP

    gene is not present in the cells) used as a control?

    E. siAsf1 causes accumulation of cells in which stage(s) of the

    cell cycle? Thus, during which stages does Asf1 function?


    F. In the space between A and B, draw a graph that would show the expected results if function of

    Asf1 were necessary during M-phase.

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