AP Biology Unit 4

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. According the data, mutant 3 had the highest percent of cells in prophase/prometaphase of all cell types and the least time in anaphase and telophase.

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?

Interphase is composed of the G1G1, SS, and G2G2 phases. Based on Figure 1, the cells typically spend 19 hours in interphase and require 20 hours total to complete one full cycle. Therefore, 1920×100=95%1920×100=95%.

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. If ethylene is not perceived by the receptors, then ripening will not occur. This best justifies the claim that ethylene initiates the signal transduction pathway.

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. Cancerous cells often produce abnormal forms of cell-cycle regulators, allowing them to divide even when it is not appropriate to do so.

A hydrophilic peptide hormone is produced in the anterior pituitary gland located at the base of the brain. The hormone targets specific cells in many parts of the body. Which of the following best explains a possible mechanism that would enable the hormone to efficiently reach all of the target cells in the body?

The hormone is released into the bloodstream where it can be transported to all cells with the correct receptors. The bloodstream is the most effective way to distribute a hormone that has to reach multiple target cells that are relatively long distances from the source of the hormone.

Figure 1 represents the relative time and sequence of the phases of the cell cycle. Which statement best predicts why a cell's progression through the cell cycle might be halted at the G1/S checkpoint?

There are not enough nucleotides available to construct new DNA. DNA replication, which occurs during SS phase, requires free nucleotides. If nucleotides are unavailable, the G1G1/SS checkpoint halts the cell cycle to conserve energy.

Researchers tracked the amount of DNA (measured in picograms) over time beginning with a single cell and continuing through several rounds of cell division. The researchers observed threadlike chromosomes prior to cell division. The threadlike chromosomes disappeared from view shortly after each division. The amount of DNA in picograms per cell over several rounds of cell division is shown in Figure 1. Which of the following statements is consistent with the data in Figure 1?

There is a change from 3 to 6 picograms of DNA because DNA is replicated before each round of cell division. The change from 3 to 6 picograms of DNA prior to replication indicates that the DNA has been replicated. The replicated DNA is condensed into chromosomes during cell division or mitosis. This ensures that the complete genome from a parent cell is passed on to two genetically identical daughter cells.

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. Table 1. Duration (in minutes) of yeast cell cycle phases in a nutrient-rich environment and a nutrient-poor environment 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?

Yeast cells in the nutrient-rich environment spend 96 minutes in the cell cycle compared to 161 minutes in the nutrient-poor environment. The percent can be determined by dividing 161 by 96, which results in 1.681.68 or 168 percent.

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. 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. Phosphorylase kinase is activated by protein kinase A, which is activated by binding to cyclic AMPAMP. Cyclic AMPAMP phosphodiesterase causes the deactivation of protein kinase A by lowering the intracellular levels of cyclic AMPAMP. Inhibiting cyclic AMPAMP phosphodiesterase will result in protein kinase A remaining active, which will result in phosphorylase kinase remaining active.

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?

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

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% .The DNADNA of a typical eukaryotic cell is replicated in the SS phase of the cell cycle, which occurs between the G1G1 and G2G2 phases. DNADNA replication typically results in a 100%100% increase in the DNADNA content of a cell.

Which of the following steps in a signaling pathway typically occurs first once a chemical messenger reaches a target cell?

A ligand binds to a receptor. The chemical messenger (ligand) first binds to a receptor, which then changes shape to initiate the signaling pathway.

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−9ced−9 gene led to excessive cell death in C. elegans. If ced−9 acts as a regulator and normally inhibits apoptosis, then if it loses function, more cell death will occur

During a fight-or-flight response, epinephrine is released into the body's circulatory system and transported throughout the body. Some cells exhibit a response to the epinephrine while other cells do not. Which of the following justifies the claim that differences in components of cell signaling pathways explain the different responses to epinephrine?

Cell signaling depends on the ability to detect a signal molecule. Not all cells have receptors for epinephrine. Only cells with such receptors are capable of responding. Cell signaling starts with the reception of the signal. Not all cells are equipped to receive all signals. Only those cells with the correct receptor to a signal will be able to respond to a signal such as epinephrine

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

Cells with inactive GSK3βGSK3β fail to trigger apoptosis. If apoptosis cannot be initiated in cells with GSK3βGSK3β mutations, those cells are more likely to proliferate, which could lead to cancer.

An antigen can induce an immune response in a host organism. Antigens are targeted by antibodies that are produced by the organism's immune system in response to contact with the antigen. Antibodies are specific to antigens. Many different cell types are involved in immune responses. Which of the following best describes the role of cell-to-cell communication during a response to an invasion of antigens?

Chemicals that are secreted from antigen-presenting cells then activate helper T cells. Cell signaling pathways are activated by cell-to-cell communication.

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. This statement accurately describes changes in the chromosome number during the different stages of cell division as represented in the graph. During prophase and metaphase, each chromosome is composed of two chromatids. During anaphase, the two chromatids separate to the opposite ends of the cell, doubling the number of chromosomes in the cell. The number of DNADNA strands in the cell has not changed, only how they are organized. During cytokinesis, the cell is divided into two daughter cells, each containing half of the chromosomes found in the parent cell during anaphase and telophase

Notch is a receptor protein displayed on the surface of certain cells in developing fruit fly embryos. Notch's ligand is a membrane-bound protein called Delta that is displayed on the surface of adjacent cells. When Notch is activated by its ligand, the intracellular tail of the Notch protein becomes separated from the rest of the protein. This allows the intracellular tail to move to the cell's nucleus and alter the expression of specific genes. Which of the following statements best explains Delta's role in regulating cell communication through the Notch signaling pathway?

Delta restricts cell communication to short distances within a developing embryo.Delta restricts cell communication to short distances by requiring direct cell-to-cell contact for activation of the Notch signaling pathway.

Blood clots are formed by a positive feedback loop. Two pathways exist, the extrinsic and intrinsic pathways, which converge during clot formation. There are many clotting factors involved, most of which are proteins. Vitamin K is required for the formation of the active form of several of the clotting factors, including Factor X. A simplified model of the blood clotting process is shown in Figure 1. Warfarin is a drug used to treat certain blood clots. Warfarin blocks the formation of the active form of vitamin K-dependent clotting factors. Based on the model, which of the following best predicts the effects of warfarin on a patient?

Factor X will not be activated, which will prevent thrombin from forming. Vitamin K is required for the synthesis of Factor XX and warfarin inhibits that process; thus, clots are prevented from forming.

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. Glycogen phosphorylase catalyzes the breakdown of glycogen, which is a catabolic process. Consequently, the statement helps justify the researcher's claim.

Signal transduction may result in changes in gene expression and cell function, which may alter phenotype in an embryo. An example is the expression of the SRY gene, which triggers the male sexual development pathway in mammals. This gene is found on the Y chromosome. Which statement provides the evidence to justify the claim that signal transduction may result in an altered phenotype?

If the SRYSRY gene is absent or nonfunctional, the embryo will exhibit female sexual development. The SRYSRY gene must be present and functional for normal male sexual development. It is the proper functioning of the SRYSRY gene that is important, and this is the best statement to support the claim.

A person's blood glucose level fluctuates during the day, as represented in Figure 1. Two hormones, insulin and glucagon, are directly involved in regulating the blood glucose level to maintain a healthy level. Insulin acts to lower the blood glucose level, and glucagon acts to increase the blood glucose level. Which of the following best predicts what will happen to the blood glucose level if the person has another meal at 5 p.m.?

Immediately after the meal, the blood glucose level will increase, and then insulin will be secreted to counter the increase. The blood glucose levels increase due to the nutrients taken in. This increase is a signal for the pancreas to release more insulin that will stimulate cells to take in the excess glucose. As a result, the blood glucose level will then decrease.

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. Based on Figure 1, the epinephrine signaling pathway involves enzymes activating other enzymes. For example, the pathway includes several protein kinases, enzymes that catalyze the transfer of a phosphate group from ATPATP to a protein substrate. As represented in Figure 1, protein kinase A catalyzes the transfer of a phosphate group from ATPATP to phosphorylase kinase, which results in the activation of phosphorylase kinase. The activated phosphorylase kinase activates glycogen phosphorylase in a similar manner.

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 cell division will lead to the formation of a tumor. Growth factors are important signaling molecules that trigger cells to divide at the correct rate and correct time. An EGFREGFR that is active when a growth factor is absent would lead to increased cell division. Uncontrolled cell growth will likely result in a tumor.

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. When activated, adenylyl cyclase accelerates a reaction in which ATPATP is converted to cyclic AMPAMP, which acts as a second messenger in the epinephrine signaling pathway.

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 signal transduction pathway, cyclic AMPAMP acts as a second messenger by relaying the signal from the plasma membrane to cytosolic enzymes. The signal is amplified inside the cell by the production of many cyclic AMPAMP molecules, which then activate enzyme molecules that are capable of catalyzing a specific reaction repeatedly.

Metformin is a drug used to treat type 2 diabetes by decreasing glucose production in the liver. AMP-activated protein kinase (AMPK) is a major cellular regulator of glucose metabolism. Metformin activates AMPK in liver cells but cannot cross the plasma membrane. By blocking AMPK with an inhibitor, researchers found that AMPK activation is required for metformin to produce an inhibitory effect on glucose production by liver cells. Which of the following best describes the component that metformin represents in a signal transduction pathway that regulates glucose production in the liver?

It is a ligand that activates the signal transduction pathway of the activation of AMPK. Since metformin does not cross the membrane, it is likely a ligand that binds to a receptor on the surface of the plasma membrane, initiating the signal transduction pathway.

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. 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?

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. According to the figure, the mean cell doubling time of Zea mays seedling root tips in compact sand is less than in loose sand. A lower mean cell doubling time indicates an increased rate of mitotic cell division for cells of root tips in compact sand.

Figure 1 is a proposed model of the feedback system controlling erythrocyte (red blood cell) production. 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. Erythropoietin production is triggered by a negative feedback mechanism. When kidney cells detect low oxygen levels, the kidney secretes more erythropoietin, which triggers the bone marrow to increase erythrocyte production.

Phosphofructokinase (PFK) is a key enzyme in glycolysis. ATP is one of the two substrates for the reaction catalyzed by PFK. ATP is also an allosteric regulator of PFK. Figure 1 shows the enzyme-substrate interactions of PFK. A researcher found a mutation that resulted in the PFK enzyme being unable to bind ATP to the allosteric site. Which of the following best predicts the effect of the mutation?

Negative feedback regulation does not occur, so the enzyme will be active when glycolysis is not needed. The reaction is normally inhibited when ATPATP binds to the allosteric site and changes the shape of the active site to the point where it can no longer bind to the substrate. The mutation will not allow this inhibition to occur, and the enzyme will be active even at high ATPATP concentrations.

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?

Seventy-five percent of the virus-infected cells are found in mitosis. The virus stimulates frequent cell division. One hundred fifty out of 200 is 75 percent. The virus activates cells currently in the G0G0 phase, leading to rapid cell growth and division.

In flowering plants, plasmodesmata are narrow channels through cell walls that connect the cytoplasms of adjacent cells. An explanation of how plant cells communicate across cell walls will most likely refer to the diffusion through plasmodesmata of which of the following?

Small, water-soluble molecules. Because plasmodesmata are narrow channels through plant cell walls, communication between adjacent cells most likely involves the diffusion of small, water-soluble molecules through the plasmodesmata, which connect the cytoplasms of the adjacent cells.

which of the following statements correctly links a stage of the cell cycle with the event occurring at that stage?

Synthesis of sufficient DNADNA for two daughter cells occurs in stage II. Stage II represents the S (synthesis) phase of interphase. The genetic information (DNA) is doubling. If this did not occur, the daughter cells formed as a result of the cell cycle would have too little genetic information (chromosomes). This process is visible on the graph, as the copies of genetic information increase from one to two copies.

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

The SRYSRY gene produces a protein that binds to specific regions of DNADNA in certain tissues, which affects the development of these tissues. SRYSRY activation results in a signal transduction pathway that produces the male phenotype. SRYSRY activation produces transcription factors that bind to specific regions of DNADNA and results in male sexual development.

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

The amount of DNADNA is halved as the cell divides into two daughter cells. During mitosis, sister chromatids are separated, two nuclei form, and cytokinesis results in the formation of two new cells. Each daughter cell has the same number of chromosomes as the original parent cell.

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. Activation of the G protein requires the exchange of GDPGDP for GTPGTP. The irreversible binding of GDPGDP to the G protein will block activation of the G protein, which will prevent epinephrine stimulation of glycogen breakdown. Consequently, the intracellular concentration of glycogen will increase.

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 FGFRFGFR proteins. The irreversible association of FGFRFGFR proteins will most likely result in the permanent activation of the FGFRFGFR signaling pathway. Because the FGFRFGFR signaling pathway regulates cell proliferation, the irreversible association of FGFRFGFR proteins will result in uncontrolled cell proliferation

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 A produced by the cell. Which of the following predictions is the most likely consequence of the mutation?

The molecule that normally binds to protein AA will no longer attach, deactivating the cellular response. In this signal transduction model, the molecule does not enter the cell but binds to the extracellular surface receptor of protein AA, thus causing a cascade reaction that produces the cellular response. Ligand binding and activation depends upon the ligand, and the receptor have the appropriate complementary shapes. Since the specified mutation changes the shape of the ligand-binding site, the cascade will not be activated, and the cell will not respond to the presence of the ligand.

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?

The number of cells that were in metaphase equals 7, and the total number of mitotic cells equals 38. The percent of mitotic cells in metaphase is calculated as follows: divide 7 by 38 and multiply by 100. The correct answer is 18 percent.

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. In vertebrate immune responses, cell surface proteins, including MHCMHC proteins and T cell receptors, mediate cell communication over short distances by interacting directly with proteins on the surfaces of other cells. In many cases, the protein-protein interaction activates signal transduction pathways that control specific cellular responses. The interaction by cell surface proteins is an example of cell communication that is limited to short distances because the communicating cells must be near to each other.

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. Thrombin is involved in a positive feedback loop. When activated, thrombin activates clotting factors that convert prothrombin to more thrombin. Activated thrombin also catalyzes the conversion of fibrinogen to fibrin, which is an important step in blood clot formation. Although activated clotting factors will catalyze the conversion of prothrombin to thrombin, inhibiting thrombin activity with argatroban will interfere with the positive feedback loop that generates more active thrombin. A decrease in the rate of thrombin formation will result in a decrease in the rate of fibrin formation.

The beta-2 adrenergic receptor is a membrane-bound protein that regulates several cellular processes, including the synthesis and breakdown of glycogen. The receptor binds specifically to the hormone epinephrine. The binding of epinephrine to the beta-2 adrenergic receptor triggers a signal transduction cascade that controls glycogen synthesis and breakdown in the cell. A simplified model of the signal transduction cascade is represented in Figure 1. Which of the following outcomes will most likely result from the inactivation of the beta-2 adrenergic receptor?

The rate of glycogen synthesis in the cell will increase. Based on Figure 1, activation of the beta-2 adrenergic receptor results in the stimulation of glycogen breakdown and the inhibition of glycogen synthesis. The immediate effect of inactivating the beta-2 adrenergic receptor will be an increase in the rate of glycogen synthesis in the cell because glycogen synthase will no longer be inhibited. Also, glycogen breakdown in the cell will no longer be stimulated because glycogen phosphorylase will most likely be deactivated.

The insulin receptor is a transmembrane protein that plays a role in the regulation of glucose homeostasis. The receptor's extracellular domain binds specifically to the peptide hormone insulin. The receptor's intracellular domain interacts with cellular factors. The binding of insulin to the receptor stimulates a signal transduction pathway that results in the subcellular translocation of GLUT4, a glucose transport protein that is stored in vesicles inside the cell. A simplified model of the insulin receptor-signaling pathway is shown in Figure 1. Which of the following statements best predicts the effect of a loss of function of the insulin receptor's intracellular domain?

The storage of GLUT4GLUT4 in vesicles inside the cell will increase. The insulin receptor's intracellular domain is required for the stimulation of the signal transduction pathway. If the signal transduction pathway is not stimulated by the insulin receptor, the GLUT4GLUT4 vesicles will not be translocated to the plasma membrane. Consequently, the storage of GLUT4GLUT4 in vesicles inside the cell will increase.

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. Because the cell cycle arrest occurs in telophase, the yeast cells will progress through the cell cycle, including replicating their chromosomes in the S phase, and will enter the M phase but will fail to complete mitosis and cytokinesis.

Adjacent plant cells have narrow channels called plasmodesmata that pass through the cell walls of the connected cells and allow a cytoplasmic connection between the cells. Which of the following statements best describes a primary function of plasmodesmata?

They allow the movement of molecules from one cell to another, enabling communication between cells. Plasmodesmata are channels through which cytosol exchange can occur, moving select molecules directly between cells. This enables cells enclosed by a cell wall to communicate.

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?

Uncontrolled cell proliferation. A loss of p53 function will result in unregulated cell proliferation because the p21 protein will not be synthesized. In the absence of the p21 protein, a cell will continue to progress through the cell cycle without stopping

G proteins are a family of receptor proteins that are involved in transmitting signals from outside a cell to inside a cell. When a signaling molecule binds to a G protein, the G protein is activated. The G protein then activates an enzyme that produces a second messenger called cAMP. Which of the following describes a critical role of cAMP during the transduction stage of a G protein signal transduction pathway?

cAMP results in the activation of an enzyme that amplifies the signal by acting on many substrate molecules. Typically, cAMP immediately activates protein kinase AA, which phosphorylates various other proteins. Kinases are a type of enzyme that activates proteins by transferring a phosphate group from ATPATP. Kinases are involved in many signaling pathways in a wide variety of organisms.