Cell Division

A group of researchers cultured yeast cells in a nutrient-rich environment and a nutrient-poor environment and observed the duration of the stages of their cell cycles. The results of their study are summarized in Table 1. The cell cycle of yeast cells in the nutrient-poor environment is approximately what percent of the cell cycle of yeast cells grown in the nutrient-rich environment?

A. 168

Glycogen sythetase kinase 3 beta is a protein kinase that has been implicated in many types of cancer. Depending on the cell type, the gene for glycogen synthetase kinase 3 beta (GSK3β) can act either as an oncogene or as a tumor suppressor.

A. Cells with inactive GSK3β fail to trigger apoptosis.

Which of the following best describes the role of mitosis in the cell cycle?

A. Distributing replicated chromosomes to daughter nuclei.

A researcher is conducting an experiment in which cells in different phases of the cell cycle are fused together. The researcher then records what happens to the nuclei of the resulting cell (Table 1). Which of the following research questions is best addressed by the experiment?

A. How do chemical messengers affect a cell's transition between the phases of the cell cycle?

FIgure 1. Model of crossing over between homologous chromosomes, indicating crossing over rate of selected loci. During prophase I replicated homologous chromosomes pair up and undergo synapsis. What testable question is generated regarding synapsis and genetic variability by Figure 1?

A. Is the distance between two gene loci related to crossover rate?

Scientists have found that DNA methylation suppresses crossing-over in the fungus Ascobolus immersus. Which of the following questions is most appropriately raised by this specific observation?

A. Is the level of genetic variation in the gametes related to the amount of DNA methylation observed?

The diploid number of chromosomes in the cell of a domesticated dog is 78. Which of the following options includes the correct number of chromosomes in a cell after each cellular process (G2 checkpoint, meiosis, and fertilization, respectively)?

B. After G2 checkpoint: 78 After Meiosis: 39 After fertilization: 78

Maturation promoting factor, MPF, is a cyclin-CDK complex that catalyzes the phosphorylation of other proteins to start mitosis. The activity level of MPF is dependent on the relative concentrations of the cyclin and CDK components of MPF. Based on Figure 1, which of the following describes the role of cyclin in the regulation of the cell cycle?

B. During M phase, the cyclin level peaks, resulting in an increased binding frequency with CDK.

Cancer can result from a variety of different mutational events. Which of the following is LEAST likely to result in the initiation of a cancerous tumor?

C. A defect in a cell-cycle checkpoint prevents a cell from entering the S phase.

Which of the following statements correctly describes the chromosomes in each daughter cell at the end of meiosis 1?

C. Each daughter cell contains 12 chromosomes, each composed of two chromatids. Each chromosome is one of a pair of homologous chromosomes from the parent cell, with the other homologue found in the other daughter cell.

Which of the following questions about genetic diversity could most appropriately be answered by analysis of the model in Figure 1?

C. How does the independent assortment of the two sets of homologous chromosomes increase genetic diversity?

Researchers performed an experiment to determine the effect of certain genetic mutation on mitosis in tropical fruit fly embryos. They determined the percentage of cells in each of four phases of mitosis as shown in Figure 1. Which of the following patterns is shown by the data?

C. In mutant 3 cells, more time is spent in prophase/prometaphase than in the later stages of mitosis.

Which of the following best explains why triploid bananas do not produce seeds?

C. The production of gametes is disrupted because of unequal pairing of homologous chromosomes during meiosis.

Researches have identified a molecule produced by Ecteinascidia turbinata, a marine invertebrate, from which the drug trabectedin is produced. Soft-tissue tumors treated with trabectedin rapidly decreased in size. In a preliminary study, healthy cells and tumor cells sampled from the skin cancer patients treated with trabectedin were collected, and several characteristics of the cells were observed. The observed results of the study are shown in the table. Which of the following best explains the most likely method by which this antitumor drug works?

C. Trabectedin interferes with the duplications of DNA during interphase and thus prevents cancer cells from passing the G2 checkpoint.

What is the expected percent change in the DNA content of a typical eukaryotic cell as it progresses through the cell cycle from the start of the G1 phase to the end of the G2 phase?

D. +100%

Researchers determined the average amount of time that a particular type of eukaryotic cell spends in each phase of the cell cycle. The data collected by the researchers are represented in FIgure 1. Based on Figure 1, what percent of the time required to complete a full cycle do the cells typically spend in interphase?

D. 95%

Both mitosis and meiosis begin with a parent cell that is diploid. Which of the following best describes how mitosis and meiosis result in daughter cells with different numbers of chromosomes?

D. Mitosis produces two identical diploid daughter cells after one round of division. Meiosis produces four haploid daughter cells after two rounds of division.

Which of the following best describes how the amount of DNA in the cell changes during M phase?

D. The amount of DNA is halved as the cell divides into two daughter cells.

Based on the model of eukaryotic cell cycle regulation shown in the figure, which of the following best describes the effect of a drug that blocks the production of the mitotic cyclin?

D. The cell would be prevented from entering mitosis, and the cell would stop dividing.

Cancer cells behave differently than normal body cells. For example, they ignore signals that tell them to stop dividing. Which of the following conditions will most likely cause a normal body cell to become a cancer cell?

D. The environment contains mutagens that would induce mutations that affect cell-cycle regulator proteins.