Bio 8 - Chapter 16: The Cell Cycle

Textbook Reference: The Eukaryotic Cell Cycle Feedback A: Incorrect. G1 and G2 are the "gap" phases of the cell cycle during which the cell simply grows. DNA synthesis does not occur during either of those phases. Feedback B: Correct! Interphase is the part of the cell cycle in which the chromosomes are decondensed and spread throughout the nucleus. Cell growth and DNA synthesis take place during interphase, which includes G1, S, and G2, in preparation for mitosis (M phase). Feedback C: Incorrect. G0 represents an exit from the cell cycle, when a cell does not divide yet remains metabolically active. Feedback D: Incorrect. M phase is the phase in which nuclear division occurs, and it happens only after interphase, during which cell growth and DNA replication occur.

1. Interphase is defined as

Answer: d

a. Anaphase I b. S phase c. Prophase II d. Prophase I

Answer: a

a. Cdk inhibitors. b. cyclins. c. oncogenes. d. growth factors.

Answer: d

a. Condensins b. Golgi matrix proteins c. Nuclear lamins d. Histone H3

Answer: b

a. activation of protein kinases by MPF. b. ubiquitin-mediated proteolysis of key proteins. c. binding of an inhibitory protein to MPF. d. depolymerization of the mitotic spindle.

Answer: c

a. centrosome. b. kinetochore. c. centromere. d. centriole.

Answer: a

a. in G0, or quiescent, phase. b. actively proliferating. c. stem cells. d. undergoing meiosis.

Answer: b

a. the G1 and G2 phases. b. the G1, G2, and S phases. c. G0, the quiescent phase. d. M phase.

Textbook Reference: The Eukaryotic Cell Cycle Feedback A: Incorrect. The MCM proteins bind replication origins only during G1, ensuring that DNA is replicated only once per cycle. Feedback B: Incorrect. Chromosome misalignment is an M phase checkpoint control. Feedback C: Correct! The G2 checkpoint ensures that the genome has been entirely replicated and that damaged DNA has been repaired prior to entry into M phase. Feedback D: Incorrect. The G1 checkpoint is mediated by the action of p53.

10. The G2 cell cycle checkpoint detects

Textbook Reference: Regulators of Cell Cycle Progression Feedback A: Incorrect. This is a true statement. Cyclin B and Cdc2 form a complex that is known as MPF. Feedback B: Incorrect. This is a true statement. Cyclin B begins to be synthesized in S phase, accumulates throughout S and G2, and is rapidly degraded at the end of M phase. Feedback C: Incorrect. This is a true statement. Cyclin B binds to Cdc2 and activates its kinase activity. Feedback D: Correct! This is a false statement. Cyclin B protein levels oscillate throughout the cell cycle, but its activity does not change.

11. Which of the following statements about cyclin B is false?

Textbook Reference: Regulators of Cell Cycle Progression Feedback A: Correct! p15 inhibits Cdk4, 6/cyclin D complexes; p21 inhibits several Cdk/cyclin complexes to block progression of the cell cycle at G1. Feedback B: Incorrect. Cyclins are a class of proteins whose levels oscillate with the cell cycle and that bind and activate Cdk's. Feedback C: Incorrect. Oncogenes are genes, not proteins. Some oncogenes stimulate cell division. Feedback D: Incorrect. Growth factors are extracellular proteins that stimulate cell division. p21 and p15 act intracellularly to inhibit cell division by binding Cdk/cyclin complexes.

12. The p21 and p15 proteins are examples of

Textbook Reference: Regulators of Cell Cycle Progression Feedback A: Incorrect. This is a true statement. Cyclin D1 in complex with Cdk4 and Cdk6 drives cells through the restriction point. Feedback B: Incorrect. This is a true statement. Cyclin D1 synthesis is rapidly induced in response to growth factor stimulation through signaling pathways such as Ras/Raf/MEK/ERK. Feedback C: Incorrect. This is a true statement. Cyclin D1 protein levels fall due to proteolytic degradation when growth factors are removed. The cell cycle will arrest if this occurs prior to passage through the restriction point. Feedback D: Correct! This is a false statement about cyclin D1. It is not always present, though it does require interaction of Cdk4 and Cdk6.

13. Which of the following statements regarding cyclin D1 is false?

Textbook Reference: The Events of M Phase Feedback A: Incorrect. Prophase is the first stage of mitosis, and chromosome condensation occurs at this time. Feedback B: Correct! S phase, when the cell's DNA becomes duplicated, occurs before mitosis, during interphase. Feedback C: Incorrect. Metaphase is the stage in mitosis in which the chromosomes align themselves along the central plate of the spindle. Feedback D: Incorrect. Anaphase is the stage of mitosis in which the sister chromatids separate and move to opposite ends of the spindle.

14. Which of the following is not one of the phases of mitosis?

Textbook Reference: The Events of M Phase Feedback A: Incorrect. The centrosomes are microtubule-organizing centers from which the microtubules emanate during the formation of the spindle. Feedback B: Incorrect. This is a structure consisting of several proteins bound to the centromere that mediates movement of chromosomes along the spindle. Feedback C: Correct! The centromere is a sequence of DNA where the sister chromatids are held together prior to their migration to opposite poles of the spindle. Feedback D: Incorrect. The centriole is a microtubular structure in the centrosomes of most animal cells.

15. The sequence of DNA on each chromosome where the sister chromatids are held together is called the

Textbook Reference: The Events of M Phase Feedback A: Incorrect. Condensins are involved in condensing the chromosomes during mitosis and are directly phosphorylated by Cdk1/cyclin B. Feedback B: Incorrect. Golgi matrix proteins are phosphorylated by Cdk1/cyclin B and initiate Golgi breakdown. Feedback C: Incorrect. The nuclear lamins are phosphorylated by Cdk1/cyclin B, leading to the breakdown of the nuclear envelope. Feedback D: Correct! Although histone H3 is phosphorylated during mitosis, the kinase has not yet been identified.

16. Which of the following are not phosphorylated by the Cdk1/cyclin B complex during mitosis?

Textbook Reference: The Events of M Phase Feedback A: Incorrect. Activation of protein kinases by MPF is involved in earlier steps in mitosis. Feedback B: Correct! MPF activates the anaphase-promoting complex, which is a ubiquitin ligase. As a result, key proteins such as Scc1, which links sister chromatids together, and cyclin B are degraded. Feedback C: Incorrect. The metaphase/anaphase transition occurs primarily via ubiquitin-mediated degradation of key proteins. Feedback D: Incorrect. This does not occur until telophase, once the chromosomes have segregated and cytokinesis is about to occur.

17. The progression from metaphase to anaphase is triggered by

Textbook Reference: Meiosis and Fertilization Feedback A: Incorrect. By anaphase I the homologous chromosomes have segregated and are moving to opposite poles of the nucleus. Feedback B: Incorrect. S phase, when the chromosomes are replicated, occurs during interphase, before the onset of meiosis. Feedback C: Incorrect. Prophase II occurs after the maternal and paternal chromosomes have segregated to daughter cells. During meiosis II sister chromatids from a single chromosome segregate from one another. Feedback D: Correct! During prophase I homologous chromosomes are aligned in close proximity to one another, and it is during this phase that crossovers between maternal and paternal chromosomes occur.

18. During what phase of meiosis does recombination between maternal and paternal chromosomes occur?

Textbook Reference: Meiosis and Fertilization Feedback A: Incorrect. CSF acts through a kinase cascade to inhibit the anaphase-promoting complex, thus arresting the cell in metaphase II. Feedback B: Incorrect. Mos is a protein kinase and a critical component of cytostatic factor (CSF), which is responsible for arresting oocyte development at metaphase II. Feedback C: Incorrect. Rsk is a protein kinase activated by cytostatic factor that acts to inhibit anaphase-promoting complex and thus arrest the developing oocyte in metaphase II. Feedback D: Correct! An increase in cytoplasmic calcium levels does not occur until after fertilization, and it triggers completion of meiosis.

19. Which of the following is not involved in metaphase II arrest during meiosis?

Textbook Reference: The Eukaryotic Cell Cycle Feedback A: Incorrect. M phase is mitosis. Feedback B: Incorrect. S phase is the phase in which replication takes place. Feedback C: Correct! This is also called gap 1 phase. Feedback D: Incorrect. G2 is characterized by continued cell growth and synthesis of proteins in preparation for mitosis.

2. The phase of the cell cycle that corresponds to the interval between mitosis and initiation of DNA replication is referred to as the

Textbook Reference: Meiosis and Fertilization Feedback A: Incorrect. This is a correct answer, but it is not the only correct answer. An increase in cytoplasmic calcium likely occurs through phosphatidylinositol bisphosphate signaling. Feedback B: Incorrect. This is a correct answer, but it is not the only correct answer. This exocytosis is triggered by the calcium influx. Feedback C: Incorrect. This is a correct answer, but it is not the only correct answer. Anaphase progression is triggered by activation of the anaphase-promoting complex, which is also dependent on the rise in intracellular calcium. Feedback D: Correct! All of the preceding statements are true.

20. At fertilization, the sperm binds to a receptor on the surface of the egg and fuses with the plasma membrane, initiating the development of a new diploid organism. Which of the following statements about fertilization is true?

Textbook Reference: The Eukaryotic Cell Cycle Feedback A: Correct! This is the phase in which cells are actively replicating; the radiolabeled nucleotide is incorporated into DNA that is being newly synthesized. Feedback B: Incorrect. G1 occurs prior to replication in S phase. Feedback C: Incorrect. G2 occurs after S phase and replication have been Feedback D: Incorrect. M phase is the period in which mitosis occurs.

3. You perform an experiment by incubating a radiolabeled nucleotide into the medium of a culture of cells. The cells that take up the radiolabel would be expected to be in what phase of the cell cycle?

Textbook Reference: The Eukaryotic Cell Cycle Feedback A: Correct! Early embryonic cells divide very rapidly, alternating between M and S phases. Since G1 and G2 do not occur, the cell does not have time to grow prior to cell division, and the resulting daughter cells are smaller than the mother cells. Feedback B: Incorrect. Yeast cells divide more rapidly than mammalian cells; however, they do go through G1 and G2. Feedback C: Incorrect. An average proliferating human cell goes through all phases of the cell cycle, including G1 and G2. Feedback D: Incorrect. Skin fibroblasts spend most of their time in G0, the quiescent phase. However, they can reenter the cell cycle and go through all of its phases, including G1 and G2, if stimulated to do so (for example, following an injury, when they would need to be regenerated).

4. In which of the following cell types do G1 and G2 not take place?

Textbook Reference: The Eukaryotic Cell Cycle Feedback A: Incorrect. M phase would be 4n and have twice the DNA content per cell. Feedback B: Incorrect. S phase cells would fall between 2n and 4n and in flow cytometry would be observed as the cells in the trough between 2n and 4n peaks. Feedback C: Incorrect. G2 cells would have twice the DNA content per cell and be found in the 4n peak. Feedback D: Correct! G1 cells have yet to replicate and have only a 2n, or diploid, amount of DNA.

5. DNA content can be determined using a method of flow cytometry that can determine 2n or 4n states of cells based on cell counting and fluorescent labeling of DNA. Which of the following phases would be identified through flow cytometry as 2n?

Textbook Reference: The Eukaryotic Cell Cycle Feedback A: Incorrect. This is a correct answer but not the only correct answer. In low nutrient conditions, progression will not occur. Feedback B: Incorrect. This is a correct answer but not the only correct answer. Proteins that signal mating will allow haploid yeast cells to fuse with one another instead of progressing to S phase. Feedback C: Incorrect. This is a correct answer but not the only correct answer. Yeast cells must attain a minimum size prior to entry into S phase. Feedback D: Correct!

6. In yeast, START triggers the progression from G1 to S. Which of the following are involved in regulating START?

Textbook Reference: The Eukaryotic Cell Cycle Feedback A: Incorrect. Growth factors are required to get to S phase. Feedback B: Incorrect. The growth factors need to exert control long before M phase. Feedback C: Incorrect. There are G2 checkpoints, but they typically are not controlled by growth factors. Feedback D: Correct! In the absence of growth factors, cells arrest in G1 and enter G0, remaining quiescent and awaiting a signal such as a growth factor to divide, much like quiescent fibroblasts.

7. In the absence of growth factor, most animal cells will stop cell cycle at a restriction point in what stage?

Textbook Reference: The Eukaryotic Cell Cycle Feedback A: Correct! Most adult cells are differentiated and cease proliferating, entering the G0 phase. However, many can reenter the cell cycle and resume proliferation if they are needed to replace damaged tissue. Feedback B: Incorrect. Unlike early embryonic cells, most cells in adult animals have ceased to proliferate. Feedback C: Incorrect. Stem cells are partially differentiated cells that can undergo mitosis to yield both differentiated cells and stem cells. Most adult cells are differentiated and have stopped dividing, except under circumstances in which tissue regeneration is necessary. Feedback D: Incorrect. Only germ cells undergo meiosis to yield the haploid cells necessary for sexual reproduction.

8. Most cells in an adult animal are

Textbook Reference: The Eukaryotic Cell Cycle Feedback A: Incorrect. This is a correct answer, but it is not the only correct answer. Feedback B: Incorrect. This is a correct answer, but it is not the only correct answer. Feedback C: Incorrect. This is a correct answer, but it is not the only correct answer. Feedback D: Correct! DNA damage is assessed at all three stages and is mediated by ATM and ATR, which recognize damaged or unreplicated DNA and activate a signaling pathway that arrests cell cycle, activates DNA repair, and/or initiates apoptosis.

9. Cell cycle checkpoints ensure that complete genomes are transmitted to daughter cells. DNA damage checkpoints are found in which of the following phases of the cell cycle?

Answer: d

a. Binding of a sperm to its receptor on the egg induces an increase in cytoplasmic calcium. b. Once fertilized, secretory vesicles are exocytosed, leading to an alteration in the extracellular coat of the egg to prevent additional sperm entry. c. Eggs are arrested at metaphase II of meiosis and fertilization leads to anaphase progression. d. All of the above

Answer: d

a. Cytostatic factor (CSF) b. Mos c. Rsk d. An increase in cytoplasmic calcium levels

Answer: a

a. Early embryonic cells b. Budding yeast cells c. Typical proliferating human cells d. Skin fibroblasts

Answer: d

a. G1 phase b. S phase c. G2 phase d. All of the above

Answer: d

a. It is a component of MPF. b. It accumulates throughout S and G2. c. It activates Cdc2 protein kinase. d. It cycles between active and inactive states in the cell cycle.

Answer: d

a. It is required for cell cycle progression. b. It is activated by growth factors. c. It is rapidly degraded following removal of appropriate growth factors. d. It is always present and its activity is regulated by fluctuating levels of Cdk4 and Cdk6.

Answer: d

a. M phase b. S phase c. G2 phase d. G1 phase

Answer: c

a. M phase. b. S phase. c. G1 phase. d. G2 phase.

Answer: d

a. Nutrients b. Mating factors c. Cell size d. All of the above

Answer: b

a. Prophase b. S phase c. Metaphase d. Anaphase

Answer: a

a. S phase b. G1 phase c. G2 phase d. M phase

Answer: d

a. S phase b. M phase c. G2 phase d. G1 phase

Answer: c

a. the binding of the MCM proteins to origins of replication. b. chromosome misalignment. c. unreplicated or damaged DNA. d. levels of p53.