Chapter 9 Progress Check Multiple Choice Questions

Researchers have discovered details about apoptosis (programmed cell death) by studying embryologic development of a nematode worm, Caenorhabditis elegans. Apoptosis is a normal developmental process in C. elegans. They found several genes involved in apoptosis, including ced-9 and ced-3. The ced-3 gene was found to promote cell death, and ced-9 to inhibit it. The ced-9 gene serves as a regulator that prevents apoptosis in the absence of a signal promoting apoptosis. Which of the following statements best justifies the claim that changes in the expression of ced-9 in C. elegans can affect regulation of apoptosis in the cell?

• An experiment showed that a mutation in the ced – 9 gene led to excessive cell death in C. elegans.

• An experiment showed that the ced – 9 gene normally produces a protein that promotes excessive cell death in C. elegans.

• A mutation in ced – 3 will cause ced – 9 to be incorrectly transcribed.

• Apoptosis is dependent on a signal from the ced – 9 gene in C. elegans.

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Fibroblast growth factor receptors (FGFRs) are transmembrane proteins that regulate cellular processes such as cell proliferation and differentiation. The extracellular domains of FGFR proteins bind specifically to signaling molecules called fibroblast growth factors. The intracellular domains of FGFR proteins function as protein kinases, enzymes that transfer phosphate groups from ATP to protein substrates. FGFR activation occurs when binding by fibroblast growth factors causes FGFR proteins in the plasma membrane to become closely associated with each other. The association of two FGFR proteins stimulates protein kinase activity, which triggers the activation of intracellular signaling pathways. A simplified model of FGFR activation is represented in Figure 1.

Which of the following changes in the FGFR signaling pathway is most likely to result in uncontrolled cell proliferation?

• The irreversible association of FGFR proteins

• The loss of the FGFR protein kinase function

• A decrease in the intracellular concentration of ATP

• A decrease in the extracellular concentrations of fibroblast growth factors

A model of the typical life cycle of a cell is shown in Figure 1.

Scientists have estimated that it takes yeast cells approximately 20 hours to complete the entire cycle. Table 1 shows the amount of time in each phase of the life cycle for yeast cells.

Based on Table 1, what percent of the life cycle of yeast cells is spent in DNA replication?

• 5 percent

• 10 percent

• 25 percent

• 50 percent

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Researchers grew seedlings of corn, Zea mays, in loose and compact sand. The researchers measured the amount of time required for the cells in the growing root tips of the seedlings to double in number. The mean cell doubling times for the two groups of seedlings are shown in Figure 1. [diagram_placeholder] Based on the sample means, which of the following conclusions about the cells in the growing root tips of Zea mays seedlings is best supported by the results of the experiment?

• The cells of the root tips grow to larger sizes when the seedlings are planted in compact sand than when the seedlings are planted in loose sand.

• The average rate of mitotic cell division is greater for the root tips growing in loose sand than for the root tips growing in compact sand.

• The average cell cycle time is greater for the root tips growing in compact sand than for the root tips growing in loose sand.

• More cells are produced per unit of time in the root tips growing in compact sand than in the root tips growing in loose sand.

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The relative amounts of DNA present in the nucleus of a cell at four different stages of the life cycle are shown in Figure 1.

Based on Figure 1, which of the following statements correctly links a stage of the cell cycle with the event occurring at that stage?

• Stage I represents the G2 phase of the cell cycle.

• Synthesis of sufficient DNA for two daughter cells occurs in stage II.

• Stage III includes mitosis.

• The replication of genetic material occurs in stage IV.

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Which of the following statements is consistent with the data in Figure 1?

• The cells have a haploid chromosome number of 3.

• The cells have a diploid chromosome number of 6.

• There is a change from 3 to 6 picograms of DNA because DNA is replicated before each round of cell division.

• There is a change from 6 to 3 picograms of DNA after each cell division because the chromosomes lengthen following cell division.

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NO TABLE GIVEN BY COLLEGE BOARD

A cell culture commonly used in research was selected to study the effect of a specific virus on the timing of cell cycle phases. Two separate cultures were started, one untreated and one inoculated with the virus. Both cultures were incubated under identical conditions. After a period of time, 200 cells from each culture were observed and classified as shown in Table 1. Which of the following most accurately describes an observation and an effect of the viral infection indicated by the data in Table 1?

• Normal cells spend 98 percent of their time cycling in and out of interphase. The virus reduces this to 5 percent of the time.

• Twenty percent of the virus-infected cells are in interphase. These cells are no longer part of the cell cycle.

• Forty percent of the virus-infected cells are in interphase. These cells are preparing for replication of genetic material.

• Seventy-five percent of the virus-infected cells are found in mitosis. The virus stimulates frequent cell division.

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A student used microscopy to investigate the relative lengths of the different stages of mitosis. The student prepared slides of cells isolated from a growing onion root tip and viewed the slides under a dissecting microscope. The student then made diagrams of cells that were in different stages of mitosis and counted the number of cells that were in each of those stages. The student’s data are presented in Table 1. Based on the data, the percent of the mitotic cells that were in metaphase is closest to which of the following?

• 5%

• 11%

• 18%

• 66%

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The epidermal growth factor receptor EGFR is a cell surface receptor. When a growth factor binds to EGFR, the receptor is activated. The activated EGFR triggers a signal transduction pathway, which leads to increased frequency of cell division. Which of the following best predicts the effect of a mutation that causes EGFR to be active in the absence of a growth factor?

• Increased apoptosis will lead to abnormal growth of the tissue.

• Increased cell division will lead to the formation of a tumor.

• Cells will exit the cell cycle, entering a non-dividing G0 phase.

• Fewer cells will be in any of the stages of mitosis.

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The tumor suppressor protein p53 binds to DNA and activates target genes, which results in the synthesis of p21, CD95, and other proteins. The p21 protein promotes cell-cycle arrest, whereas the CD95 protein promotes apoptosis. Which of the following will most likely result from a loss of p53 function?

• Rapid cell growth without cell division

• Immediate activation of apoptosis pathways

• Uncontrolled cell proliferation

• Increased expression of p53 target genes