Unit 4: Cell Communication & Cell Cycle Questions [MB, APClass, etc.]

A group of cells is assayed for DNA content immediately following mitosis and is found to have an average of 12 picograms of DNA per nucleus. How many picograms of DNA would be found in a nucleus at the end of G1 and the end of G2?

12; 24

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 grown in the nutrient-poor environment is approximately what percent of the cell cycle of yeast cells grown in the nutrient-rich environment?

168 (N.R = 96, N.P = 161, 161/96 = 1.677 or 168%)

Glycogen synthetase 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)(GSK3β) can act either as an oncogene or as a tumor suppressor. Which of the following best predicts how GSK3βGSK3β mutations can lead to the development of cancer?

Cells with inactive GSK3βGSK3β fail to trigger apoptosis.

The data in the table above were obtained from a study of the length of time spent in each phase of the cell cycle by cells of three eukaryotic organisms designated beta, delta, and gamma. Which of the following is the most plausible explanation for the difference in time spent in S phase by beta and gamma?

Gamma contains more DNA than beta.

The epinephrine signaling pathway plays a role in regulating glucose homeostasis in muscle cells. The signaling pathway is activated by the binding of epinephrine to the beta-2 adrenergic receptor. A simplified model of the epinephrine signaling pathway is represented in Figure 1. A researcher claims that the epinephrine signaling pathway controls a catabolic process in muscle cells. Which of the following statements best helps justify the researcher's claim?

Glycogen phosphorylase catalyzes the conversion of glycogen to glucose-1-phosphate.

(d) The scientists hope to test Sepin-1 in clinical trials with human cancer patients. The scientists claim that one way to test the efficacy of the Sepin-1 treatment will be to obtain periodic samples of the patients' cancer cells and determine the percent of cells in metaphase. Provide reasoning to support the scientists' claim.

If Sepin-1 is effective, chromatids aren't being separated as frequently. Therefore, the percent of cells in metaphase should go down.

The epinephrine signaling pathway plays a role in regulating glucose homeostasis in muscle cells. The signaling pathway is activated by the binding of epinephrine to the beta-2 adrenergic receptor. A simplified model of the epinephrine signaling pathway is represented in Figure 1. Based on Figure 1, which of the following statements best describes the epinephrine signaling pathway?

In involves enzymes activating other enzymes.

Researchers performed an experiment to determine the effect of certain genetic mutations 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?

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

The epinephrine signaling pathway plays a role in regulating glucose homeostasis in muscle cells. The signaling pathway is activated by the binding of epinephrine to the beta-2 adrenergic receptor. A simplified model of the epinephrine signaling pathway is represented in Figure 1. Which of the following statements best describes the role of adenylyl cyclase in the epinephrine signaling pathway?

It accelerates the production of a second messenger.

Ethylene causes fruits to ripen. In a signaling pathway, receptors activate transcription factors, which ultimately leads to ripening. Which of the following best supports the claim that ethylene initiates the signal transduction pathway that leads to ripening of fruit?

Loss-of-function mutations in ethylene receptors result in changes to the ripening process.

Air is less dense at very high elevations, so less oxygen is available than in the denser air at sea level. Based on the model in Figure 1, if a person travels from sea level to a high elevation location, which of the following correctly predicts the response to the decreased blood oxygen level?

More erythropoietin will be secreted from the kidneys, increasing production of erythrocytes.

Cyclic AMP phosphodiesterase is an enzyme that catalyzes the conversion of cyclic AMP to a different molecule. Which of the following best predicts the effect of inhibiting cyclic AMP phosphodiesterase in a muscle cell stimulated by epinephrine?

Phosphorylase kinase will remain active because protein kinase A will no longer be deactivated.

In the control sample, compare the peaks in the histogram in regions A, B and C. Which region shows the population of cells with the highestamount of DNA per cell?

Region C

(b) Identify an independent variable in the experiment graphed in Figure 1. Based on the data in Figure 1, identify a control that shows that Sepin-1 rather than something else in the culture medium is inhibiting the growth of the cancer cells.

Sepin-1 concentration is the independent variable. AT very low concentrations of Sepin-1, there is close to 100% viability. At higher concentrations of Sepin-1, there is low viability.

The compound eyes of arthropods contain photoreceptor cells surrounded by other cells such as cone cells and pigment cells. Scientists studied how interactions between neighboring cells in the developing eyes of larval fruit flies affect the differentiation of R7 precursor cells that normally become the photoreceptors of adult wild-type flies. One of their experiments is illustrated in Figure 1. (b) Describe how the defect in the Single-Mutant (Sev−) R7 precursor cell causes the cell to become a cone cell instead of a photoreceptor cell.

The Ras protein cannot bind to Sev RTK, so there is no signaling pathway causing the cell to become a cone cell.

A student claims that the Y chromosome contains the sex-determining region gene, known as the SRYgene, which causes male fetuses to develop testes. Which of the following provides correct information about cell signaling that supports the claim?

The SRY gene produces a protein that binds to specific regions of DNA in certain tissues, which affects the development of these tissues.

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?

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

Which mechanism is the best explanation for how the stem cell-derived inhibitor might arrest the cancer cell cycle at the G1 stage?

The inhibitor might block the activity of a cyclin or signaling molecule of the G1 checkpoint.

The epinephrine signaling pathway plays a role in regulating glucose homeostasis in muscle cells. The signaling pathway is activated by the binding of epinephrine to the beta-2 adrenergic receptor. A simplified model of the epinephrine signaling pathway is represented in Figure 1. Which of the following outcomes will most likely result from the irreversible binding of GDP to the G protein?

The intracellular concentration of glycogen will increase.

Figure 1 shows a model of a signal transduction cascade, initiated by the binding of a ligand to the transmembrane receptor protein A. A DNA mutation changes the shape of the extracellular domain of transmembrane receptor protein Aproduced by the cell. Which of the following predictions is the most likely consequence of the mutation?

The molecule that normally binds to protein A will no longer attach, deactivating the cellular response.

Vertebrate immune responses involve communication over short and long distances. Which of the following statements best helps explain how cell surface proteins, such as MHC proteins and T cell receptors, mediate cell communication over short distances?

The proteins interact directly with proteins on the surfaces of other cells.

The coagulation cascade controls blood clot formation in response to blood vessel injury. Thrombin is an enzyme that plays a key role in regulating the coagulation cascade. A simplified model of thrombin's role in regulating the coagulation cascade is represented in Figure 1. Argatroban is a competitive inhibitor of thrombin. Which of the following effects on the coagulation cascade is most likely to result from inhibiting thrombin activity with argatroban?

The rate of fibrin formation will decrease.

What does the difference in distribution tell you about the cells in the treated sample?

The treated cancer cells are arrested at the G1phase.

Compare the distribution of cells among G1, S, and G2 phases in the control and treated samples. Which statement best describes the difference(s) in the distribution of cells in the treated sample compared to the control sample?

The treated cells are mostly in the G1 phase (region A), but in the control sample, there are peaks of cells in both G1 and G2 (region C).

What treatment is being compared to the control in the experiment?

The treated glioblastoma cells were cultured in the presence of an inhibitor from umbilical cord stem cells, but the control cells were cultured without the inhibitor.

The compound eyes of arthropods contain photoreceptor cells surrounded by other cells such as cone cells and pigment cells. Scientists studied how interactions between neighboring cells in the developing eyes of larval fruit flies affect the differentiation of R7 precursor cells that normally become the photoreceptors of adult wild-type flies. One of their experiments is illustrated in Figure 1. (c) The scientists predict that the presence of activated Ras in the Double-Mutant (Sev−RasD) R7precursor cell will enable the cell to differentiate into an R7 photoreceptor cell. Based on Figure 1, evaluate the likely accuracy of their prediction.

Their prediction is supported by the data because the Ras is activated, causing a signaling pathway.

If cells are provided with nucleotides labeled with a radioactive isotope of hydrogen (3H), newly synthesized DNA will be radioactively labeled. In a set of experiments, a student-faculty research team introduced labeled T nucleotides into a culture of dividing human cells at specific times. Following a 30-minute incubation with the radiolabeled nucleotides, cells were lysed, and the DNA was isolated and tested for presence of radioactivity. Which of the following question might be answered by such a method?

What is the duration of the S phase of the cell cycle?

Taxol is an anticancer drug extracted from the Pacific yew tree that binds to microtubules and prevents their depolymerization. Which phase of mitosis or cell division would be inhibited by treatment with Taxol?

anaphase

Cytochalasin B is a chemical that disrupts microfilament formation. With which aspect of cell division would cytochalasin B interfere?

cleavage

Besides the ability of some cancer cells to divide uncontrollably, what else might logically result in formation of a tumor?

lack of appropriate cell death

Although both ends of a microtubule can gain or lose subunits, one end (called the plus end) polymerizes and depolymerizes at a higher rate than the other end (the minus end). For spindle microtubules, the plus ends are in the centre of the spindle, and the minus ends are at the poles. Motor proteins that move along microtubules specialize in walking either toward the plus end or toward the minus end; the two types are called plus end-directed and minus end-directed motor proteins, respectively. Given what you know about chromosome movement and spindle changes during anaphase, predict which type of motor proteins would be present on kinetochore microtubules.

minus end-directed motor proteins

Given what you know about chromosome movement and spindle changes during anaphase, predict which type of motor proteins would be present on nonkinetochore microtubules.

plus end-directed motor proteins

Movement of the chromosomes during anaphase would be most affected by a drug that prevents which of the following processes?

shortening of microtubules

Now look at the histogram representing the treated sample, which shows the effect of growing the cancer cells alongside human umbilical cord stem cells. In the treated sample histogram, which phase of the cell cycle has the greatest number of cells?

the G1 phase

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?

+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?

95%

The compound eyes of arthropods contain photoreceptor cells surrounded by other cells such as cone cells and pigment cells. Scientists studied how interactions between neighboring cells in the developing eyes of larval fruit flies affect the differentiation of R7 precursor cells that normally become the photoreceptors of adult wild-type flies. One of their experiments is illustrated in Figure 1. (a) Describe the first interaction that must occur between the R7 precursor cell and the R8 cell for the R7 precursor to differentiate to an R7 photoreceptor cell.

Boss has to bind to Sev RTK

Figure 1 shows the number of chromosomes observed in an actively dividing human cell at each stage of cell division. Which of the following presents a correct interpretation of the changes in chromosome number depicted in Figure 1?

Chromosomes enter metaphase containing two chromatids attached by a centromere. During anaphase, the chromatids are separated, each becoming a chromosome. Cytokinesis distributes the chromosomes into two separate cells.

If cells are provided with nucleotides labeled with a radioactive isotope of hydrogen (3H), newly synthesized DNA will be radioactively labeled. In a set of experiments, a student-faculty research team introduced labeled T nucleotides into cultures of dividing human lymphocytes at specific times. A pathogen was introduced into one culture prior to the start of the experiment, and another culture was left untreated as a control. Following a 24-hour incubation with the radiolabeled nucleotides, cells were lysed, and the DNA was isolated and tested for presence of radioactivity. The research team found that lymphocytes exposed to a pathogen incorporated three times the amount of labeled nucleotide as the control. Which of the following hypotheses might explain these observations?

Infection causes lymphocytes to reproduce more rapidly.

In a certain signal transduction pathway, the binding of an extracellular molecule to a cell-surface protein results in a rapid increase in the concentration of cyclic AMP inside the cell. The cyclic AMP binds to and activates cytosolic enzymes that then activate other enzymes in the cell. Which of the following statements best describes the role of cyclic AMP in the signal transduction pathway?

It acts as a second messenger that helps relay and amplify the signal within the cell.

In the control sample histogram, does the population of cells in the S phase show a distinct peak? Why or why not?

No; the DNA content per cell changes as the S phase progresses, so the cells in S phase have a range of fluorescence levels.

The relative amount of DNA in a cell at various stages of the cell cycle is shown in Figure 1. Which of the following best describes how the amount of DNA in the cell changes during M phase?

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

Glucocorticoids are steroid hormones that control cellular responses through several different signaling pathways. One of the signaling pathways involves the glucocorticoid receptor, an intracellular protein that is activated by binding to a glucocorticoid molecule. A simplified model of the glucocorticoid receptor signaling pathway is represented in Figure 1. Which of the following statements best predicts the effect of a mutation that results in a loss of the glucocorticoid receptor's ligand binding function?

The glucocorticoid receptor will remain associated with the accessory proteins.

(a) Identify the point in mitosis at which separase cleaves the protein complex that holds sister chromatid pairs together. In normal cells, separase is kept in an inactive state until it is needed. Explain how the progression of cells past sequential cell cycle checkpoints and the activity of enzymes such as separase is controlled by interactions between two major groups of regulatory proteins.

The phase at with separase cleaves sister chromatid pairs is anaphase. Cyclins and CDL proteins induce the cells to move to different parts of the cell cycle.

The compound eyes of arthropods contain photoreceptor cells surrounded by other cells such as cone cells and pigment cells. Scientists studied how interactions between neighboring cells in the developing eyes of larval fruit flies affect the differentiation of R7 precursor cells that normally become the photoreceptors of adult wild-type flies. One of their experiments is illustrated in Figure 1. (d) The Sev RTK is expressed in more cell types than just R7 precursor cells, and it appears to be important in determining the phenotypes of these other cells. Explain how one receptor can induce different phenotypes in different cell types.

The proteins that interact may differ causing one receptor to induce different phenotypes in different cell types.

(c) Based on the data in Table 2, describe the general relationship between the sensitivity of cells to Sepin-1 and the concentration of separase in the cells. Use the Figure 1 data to calculate the ration between the amount of Sepin-1 required to kill 50% of the cells in the cell line that is most sensitive to compound and the cell line that is least sensitive to the compound.

The ratio is 1:3. The most sensitive is line A with 10. The least sensitive is D with 30. The greater the concentrations of separase, the more sensitive the cells are to Sepin-1

The data are plotted in a type of graph called a histogram, which groups values for a numeric variable on the x-axis into intervals. A histogram allows you to see how an entire group of experimental subjects (cells, in this case) are distributed along a continuous variable (amount of fluorescence). In these histograms, the bars are so narrow that the data appear to follow a curve for which you can detect peaks and dips. Each bar represents the number of cells observed to have a fluorescence level in that interval. This in turn indicates the relative amount of DNA in those cells. Which axis indirectly shows the relative amount of DNA per cell? By what relationship?

The x-axis; the DNA was stained, so there is a positive correlation between fluorescence and DNA content.

Researchers studying cell cycle regulation in budding yeast have observed that a mutation in the CDC15 gene causes cell cycle arrest in telophase when the yeast cells are incubated at an elevated temperature. Which of the following statements best predicts the effect of the cell cycle arrest on proliferating yeast cells?

The yeast cells will replicate their chromosomes but will fail to complete cytokinesis.

Identify which phase of the cell cycle is represented by each region. The regions represent the same cell cycle phases in both histograms.

region A: G1 region B: S region C: G2