AP bio unit 4, Unit 4 MCQ

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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%

If a cell in the metaphase stage of mitosis contains 20 sister chromatids, how many chromosomes will be present in the daughter cells?

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. Table 1. Number of cells in each of four different stages of mitosis Based on the data, the percent of the mitotic cells that were in metaphase is closest to which of the following?

18 percent

18% 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.

A model of the typical life cycle of a cell is shown in Figure 1. Figure 1. Typical life cycle of a eukaryotic cell 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. Table 1. Amount of time spent in each stage of the cell cycle by yeast cells Based on Table 1, what percent of the life cycle of yeast cells is spent in DNA replication?

25 percent The yeast cells spend 5 hours out of a total of 20 hours in SS phase, which is 25%

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. Figure 1. The average amount of time spent by a particular type of eukaryotic cell in each phase of the cell cycle Based on Figure 1, what percent of the time required to complete a full cycle do the cells typically spend in interphase?

Insulin, a hormone secreted by pancreatic cells, stimulates glucose uptake in skeletal muscle cells by mobilizing glucose transporter proteins (GLUT4) to the plasma membrane. As depicted in Figure 1, binding of insulin to the insulin receptor triggers an intracellular signaling cascade in which certain molecules activate other molecules in a relay of the hormone signal to cell targets. One outcome of the signaling cascade is mobilization of GLUT4 from vesicle storage sites in the cytoplasm to sites at the cell surface, where GLUT4 allows glucose to enter the cell. In type 2 diabetes, the cellular response to insulin is disrupted, and individuals with type 2 diabetes cannot properly regulate their blood glucose levels. In an investigation of the insulin signaling pathway, samples of skeletal muscle were isolated from individuals who have type 2 diabetes and from individuals who do not. The results of several experiments that were performed on the muscle samples are shown in Figure 2, Figure 3, and Figure 4. Based on the information presented, which of the following genetic changes in an individual without diabetes is most likely to result in a disrupted cellular response to insulin signaling similar to that of an individual with type 2 diabetes?

A A deletion in the gene encoding the insulin receptor that removes only the cytoplasmic domain of the protein

Antidiuretic hormone (ADH) is important in maintaining homeostasis in mammals. ADH is released from the hypothalamus in response to high tissue osmolarity. In response to ADH, the collecting duct and distal tubule in the kidney become more permeable to water, which increases water reabsorption into the capillaries. The amount of hormone released is controlled by a negative feedback loop. Based on the model presented, which of the following statements expresses the proper relationship between osmolarity, ADH release, and urine production? A As tissue osmolarity rises, more ADH is released, causing less water to be excreted as urine. B As tissue osmolarity rises, less ADH is released, causing less water to be excreted as urine. C As tissue osmolarity rises, more ADH is released, causing more water to be excreted as urine. D As tissue osmolarity rises, less ADH is released, causing more water to be excreted as urine.

A As tissue osmolarity rises, more ADH is released, causing less water to be excreted as urine.

Which of the following best describes the role of mitosis in the cell cycle? A Distributing replicated chromosomes to daughter nuclei B Dividing the cytoplasm to form four gametes C Producing organelles and replicating chromosomes D Exchanging genetic material between homologous chromosomes

A Distributing replicated chromosomes to daughter nuclei

Epinephrine is a protein hormone found in many animals. Epinephrine stimulates a signaling pathway that results in the breakdown of glycogen to glucose in the liver cells. Which of the following describes the initial steps in the process whereby epinephrine stimulates glycogen breakdown? A Epinephrine binds to a cell-surface receptor; the activated receptor stimulates production of the second messenger, cAMP. B Epinephrine binds to a cell-surface receptor; the activated receptor catalyzes the conversion of glycogen to glucose. C Epinephrine diffuses through the plasma membrane; the hormone dimerizes in the cytosol. D Epinephrine is taken into the cell by endocytosis; glycogen is converted to glucose in the endocytotic vesicle.

A Epinephrine binds to a cell-surface receptor; the activated receptor stimulates production of the second messenger, cAMP.

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?

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

Insulin, a hormone secreted by pancreatic cells, stimulates glucose uptake in skeletal muscle cells by mobilizing glucose transporter proteins (GLUT4) to the plasma membrane. As depicted in Figure 1, binding of insulin to the insulin receptor triggers an intracellular signaling cascade in which certain molecules activate other molecules in a relay of the hormone signal to cell targets. One outcome of the signaling cascade is mobilization of GLUT4 from vesicle storage sites in the cytoplasm to sites at the cell surface, where GLUT4 allows glucose to enter the cell. In type 2 diabetes, the cellular response to insulin is disrupted, and individuals with type 2 diabetes cannot properly regulate their blood glucose levels. In an investigation of the insulin signaling pathway, samples of skeletal muscle were isolated from individuals who have type 2 diabetes and from individuals who do not. The results of several experiments that were performed on the muscle samples are shown in Figure 2, Figure 3, and Figure 4. A The relatively low levels of glucose uptake in individuals with type 2 diabetes indicate that mobilization of GLUT4 to the cell surface is reduced in muscle cells of those individuals. B The relatively low levels of glucose uptake in individuals with type 2 diabetes indicate that no functional GLUT4 protein is produced in the muscle cells of those individuals. C The absence of activated insulin receptors in individuals with type 2 diabetes indicates that no insulin is secreted by the pancreatic cells of those individuals. D The absence of activated IRS-1 in individuals with type 2 diabetes indicates that no functional insulin receptor protein is produced in the muscle cells of those individuals.

A The relatively low levels of glucose uptake in individuals with type 2 diabetes indicate that mobilization of GLUT4 to the cell surface is reduced in muscle cells of those individuals.

In response to elevated blood glucose levels, beta (β) cells in the pancreas release insulin, a regulatory hormone. Insulin signals body cells to take up glucose from the blood, which returns blood glucose levels back to normal. Type 1 diabetes is an autoimmune disorder that destroys β-cells, resulting in elevated blood glucose levels. Researchers have proposed that diabetes could be treated by implanting human embryonic stem cells (hESCs) that have been induced to develop into β-cells (hESC-β). To test the proposed treatment, the researchers set up two groups of genetically identical mice and implanted the mice from one group with hESC-β cells. Several weeks after the hESC-β implant, both groups of mice were given a drug (STZ) that selectively destroys the naturally occurring mouse β-cells but does not affect the implanted hESC-β cells. Figure 1 shows a comparison of average blood glucose levels in both groups of mice. A The treatment would fail because insulin produced by implanted hESC-β cells will not stimulate glucose uptake by body cells. B The treatment would fail because the implanted hESC-β cells would require more glucose than the body can produce. C The treatment would succeed because the implanted hESC-β cells can express the gene that codes for human insulin. D The treatment would succeed because the body cells would secrete more insulin in the presence of the implanted hESC-β cells.

A The treatment would fail because insulin produced by implanted hESC-β cells will not stimulate glucose uptake by body cells.

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?

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

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.

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.

A mutation in the gene encoding G-PIP that results in a nonfunctional protein

signal transduction pathway

A series of steps linking a mechanical, chemical, or electrical stimulus to a specific cellular response.

Most cells that have become transformed into cancer cells have which of the following characteristics when compared to normal, healthy cells? A. Shorter cell cycles B. More carefully regulated rates of cell division C. Lower rates of mitosis D. Higher rates of protein translation E. Identical DNA

A. Shorter cell cycles

ADH promotes an increase in the movement of water into the bloodstream.

Damaged tissue releases chemicals that activate platelets and stimulate the formation of blood clots. Which of the following predictions about the activity of platelets best describes a positive feedback mechanism?

Activated platelets release chemicals that activate more platelets.

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.

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−9ced−9 and ced−3ced−3 . The ced−3ced−3 gene was found to promote cell death, and ced−9ced−9 to inhibit it. The ced−9ced−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−9ced−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−9ced−9 acts as a regulator and normally inhibits apoptosis, then if it loses function, more cell death will occur.

Excess intracellular iron is toxic to cells (iron-induced toxicity). Ferritin is an intracellular iron storage protein that binds excess iron. The presence of ferritin can protect cells from iron-induced toxicity. In an experiment to investigate the effects of dietary iron intake on ferritin synthesis, rats were given food containing different amounts of iron. Subsequently, the levels of ferritin protein in the liver were measured. The results are shown in Figure 1. Based on these and other data, researchers have developed the following model demonstrating how ferritin synthesis is regulated by iron. When iron levels are low, a repressor of translation, iron response protein (IRP), binds to an iron response element (IRE), which is a stem-loop structure near the 5¢ end of ferritin mRNA. When iron levels are high, intracellular iron binds to the IRP, and the iron-IRP complex dissociates from the IRE, permitting ribosomes to proceed with the translation of ferritin mRNA. Figure 2 represents the model of the regulation of ferritin mRNA translation by iron. Figure 2. Model of regulation of ferritin synthesis by iron Based on the model of ferritin synthesis presented in Figure 2, which of the following describes the role of feedback on the control of intracellular iron levels?

An increase in iron levels activates synthesis of ferritin protein. Ferritin protein in turn binds iron, thereby decreasing both free iron levels and ferritin synthesis.

Density-dependent inhibition is explained by which of the following processes?

As cells become more numerous, the cell surface proteins of one cell contact the adjoining cells, and they signal each other to stop dividing.

The mechanism of action of many common medications involves interfering with the normal pathways that cells use to respond to hormone signals. Which of the following best describes a drug interaction that directly interferes with a signal transduction pathway? A A medication causes the cell to absorb more of a particular mineral, eventually poisoning the cell. B A medication enters the target cell and inhibits an enzyme that normally synthesizes a second messenger. C A medication enters the target cell's nucleus and acts as a mutagen. D A medication interrupts the transcription of ribosomal RNA genes.

B A medication enters the target cell and inhibits an enzyme that normally synthesizes a second messenger.

In mammals, an increase in the concentration of sodium in the blood triggers the release of antidiuretic hormone (ADH) from the pituitary gland. As the concentration of sodium in the blood returns to previous levels, the release of ADH from the pituitary gland is reduced. Based on the information presented, which of the following describes the most likely role of ADH in maintaining blood osmolarity? A ADH promotes an increase in the movement of sodium into the bloodstream. B ADH promotes an increase in the movement of water into the bloodstream. C ADH promotes an increase in the excretion of water from the body. D ADH promotes an increase in the secretion of additional ADH from the pituitary gland.

B ADH promotes an increase in the movement of water into the bloodstream.

The endocrine system incorporates feedback mechanisms that maintain homeostasis. Which of the following demonstrates negative feedback by the endocrine system? A During labor, the fetus exerts pressure on the uterine wall, inducing the production of oxytocin, which stimulates uterine wall contraction. The contractions cause the fetus to further push on the wall, increasing the production of oxytocin. B After a meal, blood glucose levels become elevated, stimulating beta cells of the pancreas to release insulin into the blood. Excess glucose is then converted to glycogen in the liver, reducing blood glucose levels. C At high elevation, atmospheric oxygen is more scarce. In response to signals that oxygen is low, the brain decreases an individual's rate of respiration to compensate for the difference. D A transcription factor binds to the regulatory region of a gene, blocking the binding of another transcription factor required for expression.

B After a meal, blood glucose levels become elevated, stimulating beta cells of the pancreas to release insulin into the blood. Excess glucose is then converted to glycogen in the liver, reducing blood glucose levels.

The model shown in the figure represents the role of two hormones, calcitonin and parathyroid hormone (PTH), in maintaining normal blood calcium levels in humans. If a dietary change results in an increase in blood calcium concentration above normal levels, which of the following is the most likely effect on calcium homeostasis? A Calcitonin levels will decline, thus stimulating the release of PTH. B Calcitonin levels will rise, thus promoting the deposit of calcium into bones. C PTH levels will decline, thus stimulating the loss of calcium from bones. D PTH levels will increase, thus preventing the release of calcitonin.

B Calcitonin levels will rise, thus promoting the deposit of calcium into bones.

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. Figure 1. Blood glucose fluctuations of an individual Which of the following best predicts what will happen to the blood glucose level if the person has another meal at 5 p.m.?

B Immediately after the meal, the blood glucose level will increase, and then insulin will be secreted to counter the increase.

A researcher examining a root tip observes a plant cell with condensed sister chromatids, kinetochores with attached microtubules, and individual chromosomes that are aligned at the equatorial plate of the cell. Which of the following best describes what the next process will be in the cell?

B Paired chromatids will separate, and the new daughter chromosomes will move toward opposite poles of the cell.

Figure 1 shows a model of a signal transduction cascade, initiated by the binding of a ligand to the transmembrane receptor protein A. Figure 1. Model of signal transduction cascade incorporating 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?

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

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.

B The storage of GLUT4 in vesicles inside the cell will increase.

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

B There are not enough nucleotides available to construct new DNA

The diagram above represents a model of signal transduction pathways (I and II) in a cell that is targeted by two different hormones (H1 and H2). The components of the signal transduction pathways are identified in the figure legend. Each cellular molecule in both pathways can exist in an inactive or active form. When the components in pathway I are sequentially activated, the TAP molecules promote cell division. When the components in pathway II are sequentially activated, downstream signaling by the G protein is inhibited. Based on the model, which of the following mutations is most likely to result in a cell that will generate a cancerous tumor? A. A mutation in the gene encoding PP that results in a nonfunctional protein B. A mutation in the gene encoding G-PIP that results in a nonfunctional protein C. A mutation in the gene encoding R1 so that it is inactive even in the presence of H1 D. A mutation in the gene encoding R2 so that it is active even in the absence of H2

B. A mutation in the gene encoding G-PIP that results in a nonfunctional protein

Ethylene is an organic compound produced by ripening fruits. In a controlled experiment, researchers found that ethylene gas stimulated the ripening process in newly harvested fruits. Which of the following describes the most likely connection between natural ethylene production and fruit ripening? A. As a result of metabolic inactivity, newly harvested fruits are unable to absorb ethylene gas from the atmosphere. B. Ethylene gas is a chemical signal through which ripening fruits trigger the ripening process in other fruits. C. Because of normal phenotypic variation, only some of the fruits in a given generation are expected to produce ethylene gas. D. The rate of ethylene gas production by ripening fruits is an indicator of the relative age of an ecosystem.

B. Ethylene gas is a chemical signal through which ripening fruits trigger the ripening process in other fruits.

The brain coordinates the circulatory and respiratory systems of the human body. The control of breathing, for example, involves neural pathways among the structures represented in the figure above. One important stimulus in the control of breathing is an increase in blood CO2 concentration, which is detected as a decrease in blood pH. Which of the following best describes the physiological response to an overall increase in cellular respiration in the body? A. In response to depleted blood CO2 levels, the pH sensors send signals directly to the rib muscles, resulting in an increase in the rate of CO2 uptake by the lungs and a decrease in CO2 utilization by the brain. B. In response to low blood pH, the pH sensors send a signal to the brain, which then sends a signal to the diaphragm, resulting in an increased rate of breathing to help eliminate excess blood CO2 . C. In response to high blood pH, the pH sensors send a signal directly to the lungs, resulting in a slower rate of breathing, and the lungs send a signal back to the heart once CO2 availability has been restored. D. In response to an increased rate of breathing, the rib muscles send a signal to the brain, which then sends a signal to the heart, resulting in a decrease in heart activity and slower flow of blood through the body.

B. In response to low blood pH, the pH sensors send a signal to the brain, which then sends a signal to the diaphragm, resulting in an increased rate of breathing to help eliminate excess blood CO2 .

Which of the following is true of mitosis? A. It is also known as cytokinesis. B. It maintains the same chromosome number in the daughter cells as in the parent cell. C. It is the last phase of interphase. D. It regulates the transfer of genetic information from one daughter cell to another. E. It moves homologous chromosomes to opposite poles.

B. It maintains the same chromosome number in the daughter cells as in the parent cell.

Which of the following statements best describes how a growth factor stimulates cell division from outside a cell? A. The growth factor binds to other cells in the same area and holds them together to form a large, multicellular structure. B. The growth factor binds to receptors on the cell surface, initiating a signal transduction pathway that activates specific target genes. C. The growth factor binds to sugar molecules in the extracellular fluid and provides them to the cell as a source of energy. D. The growth factor binds to phospholipids in the plasma membrane, creating a channel through which substances enter the cell.

B. The growth factor binds to receptors on the cell surface, initiating a signal transduction pathway that activates specific target genes.

Which of the following best represents two different signaling pathways that share a second messenger?

The graph above shows changes in glucagon and insulin secretions at different concentrations of blood glucose. Which of the following feedback mechanisms is best supported by the data? A A falling glucagon level causes a rise in the insulin level, which maintains equal amounts of both hormones in the blood. B A high glucagon level causes a rise in the insulin level, which maintains high levels of both hormones in the blood. C A low glucose level causes the release of glucagon, which stimulates the release of more glucose from tissues, which in turn lowers the amount of glucagon being released. D A low glucose level causes the release of insulin, which stimulates the release of more glucose from tissues, which in turn increases the amount of insulin being released.

C A low glucose level causes the release of glucagon, which stimulates the release of more glucose from tissues, which in turn lowers the amount of glucagon being released.

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?

C Delta restricts cell communication to short distances within a developing embryo.

Many human cells can be stimulated to divide by hormonelike growth factors that bind to receptor proteins (R) on the plasma membrane and trigger an internal signal-transduction cascade. In many cases, however, the process of contact inhibition prevents mitosis when cells are in direct contact with one another. Contact inhibition occurs when proteins called cell adhesion molecules (CAMs) interact, causing them to change shape so that the growth-factor signaling proteins that normally associate with CAMs are replaced by another protein, called M. Both pathways are depicted in the figures below. Which of the following statements accurately uses the information presented to support the hypothesis that interruption of M function in a single body cell can result in cancer? A Protein 3 will be prevented from interacting with CAMs, causing the cell cycle to stop permanently. B The ras protein will remain bound to DNA, blocking expression of genes required for mitosis. C Growth-factor signaling can trigger mitosis in cells that are in direct contact with other cells. D The receptor proteins of body cells will no longer bind to growth-factor proteins.

C Growth-factor signaling can trigger mitosis in cells that are in direct contact with other cells.

In response to elevated blood glucose levels, beta (β) cells in the pancreas release insulin, a regulatory hormone. Insulin signals body cells to take up glucose from the blood, which returns blood glucose levels back to normal. Type 1 diabetes is an autoimmune disorder that destroys β-cells, resulting in elevated blood glucose levels. Researchers have proposed that diabetes could be treated by implanting human embryonic stem cells (hESCs) that have been induced to develop into β-cells (hESC-β). To test the proposed treatment, the researchers set up two groups of genetically identical mice and implanted the mice from one group with hESC-β cells. Several weeks after the hESC-β implant, both groups of mice were given a drug (STZ) that selectively destroys the naturally occurring mouse β-cells but does not affect the implanted hESC-β cells. Figure 1 shows a comparison of average blood glucose levels in both groups of mice. A Decreased insulin secretion by body cells → increased glucose uptake by mouse β-cells → increased insulin secretion by body cells B Increased insulin production by mouse β-cells → increased glucose uptake by hESC-β cells → decreased glucose metabolism by body cells C Increased insulin secretion by hESC-β cells → increased glucose uptake by body cells → decreased insulin secretion by hESC-β cells D Increased metabolism of glucose by hESC-β cells → differentiation of hESC-β cell into body cells → increased glucose production by body cells

C Increased insulin secretion by hESC-β cells → increased glucose uptake by body cells → decreased insulin secretion by hESC-β cells

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?

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

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. Figure 1. Amount of DNA in picograms per cell over several rounds of cell division Which of the following statements is consistent with the data in Figure 1?

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

The Hedgehog protein (Hh) plays a critical role during a certain period of embryo development, but it normally has no role in adults except for the maintenance of adult stem cells. However, the Hedgehog protein has been detected in 70 percent of pancreatic cancer cell samples. As illustrated in the figures below, the Hedgehog protein binds to an integral membrane protein receptor known as Patched (Ptc), thus initiating a pathway of gene expression. When Hedgehog is absent, Ptc inhibits another protein known as Smoothened (Smo), which, in turn, blocks the activation of a group of proteins collectively known as the Hedgehog signaling complex (HSC). The inactivation is the result of proteolytic cleavage of one component of the HSC complex, a transcription factor known as Cubitus interruptus (Ci). When Hedgehog is present, it binds to Ptc, which prevents the inhibition of Smo by Ptc. The result is that Ci remains intact and can enter the nucleus, where it binds to and activates certain genes. A Treating patients with a molecule that is structurally similar to Hedgehog and that will bind to and interact with Ptc in the same fashion as Hedgehog B Injecting patients with embryonic cells so that Hedgehog will bind to those cells instead of the cancer cells C Treating patients with a membrane-soluble compound that can bind to Smo and block its activity D Injecting patients with a preparation of purified membrane-soluble Ci that will enter the nuclei of the cancer cells and induce gene transcription

C Treating patients with a membrane-soluble compound that can bind to Smo and block its activity

If chemical signals in the cytoplasm control the progression of a cell to the M phase of the cell cycle, then fusion of a cell in G1 with a cell in early M phase would most likely result in the A replication of chromosomes only in the G1 cell B exiting of both cells from the cell cycle and into the G0 phase C condensation of chromatin in preparation of nuclear division in both cells D transfer of organelles from the G1 cell to the cell in the M phase

C condensation of chromatin in preparation of nuclear division in both cells

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? A. A receptor mutation results in activation of a cell-division pathway in the absence of the appropriate ligand. B. A mutation results in the loss of the ability to produce a tumor-suppressor protein. C. A defect in a cell-cycle checkpoint prevents a cell from entering the S phase. D. At the anaphase checkpoint, separation of chromatids occurs without all centromeres being attached to kinetochore microtubules from both poles.

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

Cell communication is critical for the function of both unicellular and multicellular eukaryotes. Which of the following is likely true of cell signaling? A. Cell signaling uses the highest molecular weight molecules found in living cells. B. Cell signaling has largely been replaced by other cell functions in higher mammals. C. Similar cell signaling pathways in diverse eukaryotes are evidence of conserved evolutionary processes. D. Cell signaling functions mainly during early developmental stages.

C. Similar cell signaling pathways in diverse eukaryotes are evidence of conserved evolutionary processes.

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.

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.

Hormones are chemical substances produced in one organ that are released into the bloodstream and affect the function of a target organ. Which of the following conditions is required for the target organ to respond to a particular hormone?

Cells in the target organ must have receptors that recognize and bind the hormone molecule.

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 GSK3β fail to trigger apoptosis.

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.

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 explains 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.

prophase

Chromosomes become visable, nuclear envelop dissolves, spindle forms

Metaphase

Chromosomes line up in the middle of the cell

The diagram above illustrates feedback control as exerted by the hormone thyroxine. Following surgical removal of the thyroid gland, the level of TSH in the blood will increase. Which of the following best explains this increase? A Residual blood thyroxine, from prior to thyroid gland removal, will bind to cells in the anterior pituitary, signaling more TSH secretion. B Thyroxine will remain bound to thyroxine receptors on various body cells, and these body cells will secrete additional hormones that stimulate the anterior pituitary to secrete TSH. C Thyroxine that was stored in the anterior pituitary prior to thyroid gland removal will signal more TSH secretion. D A decrease in thyroxine levels means a loss of inhibition to the hypothalamus and anterior pituitary, leading to increased TSH secretion.

D A decrease in thyroxine levels means a loss of inhibition to the hypothalamus and anterior pituitary, leading to increased TSH secretion.

Cortisol is a hormone produced in response to stress, including starvation, in humans. Which of the following is most likely an immediate effect of a starvation-induced increase in cortisol secretion? A Increased activation of the immune system B Increased urine production by the kidneys C Increased bone and collagen formation D Increased mobilization of fatty acids from fat cells

D Increased mobilization of fatty acids from fat cells

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. Figure 1. Mean cell doubling times for the growing root tips of Zea mays seedlings planted in loose or compact sand 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?

D 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.

Steroid hormones, such as testosterone, pass through the plasma membrane and bind to an intracellular protein, as shown in the diagram below. The hormone-receptor complex then enters the nucleus, where it interacts with DNA to promote transcription of a specific gene. A Histone protein synthesis will increase because histones maintain the DNA in an optimal conformation for chromosome assembly. B Ribosome production will increase because ribosomes are specific for the mRNA with which they bind during translation. C DNA replication will increase as a result of the binding of the hormone-receptor complex to the DNA. D Production of a specific mRNA will increase as a result of the binding of the hormone-receptor complex to the DNA.

D Production of a specific mRNA will increase as a result of the binding of the hormone-receptor complex to the DNA.

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.

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? A The cell cycle would proceed uncontrollably, and the cell would become cancerous. B The G1 cyclin would functionally replace mitotic cyclin, and the cell would continue dividing normally. C DNA synthesis would be prevented, and the cell would stop dividing. D The cell would be prevented from entering mitosis, and the cell would stop dividing.

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

Two types of cholesterol transport proteins, low-density lipoproteins (LDL) and high-density lipoproteins (HDL), bind to cholesterol and carry it through the bloodstream. Familial hypercholesterolemia (FH) is characterized by high cholesterol levels in the blood, which can lead to cardiovascular disease. FH is associated with a loss-of-function mutation of a gene that encodes LDL receptors in liver cells. Individuals who are heterozygous produce lower-than-normal amounts of the LDL receptors, and individuals who are homozygous for the mutant allele have no LDL receptor function. Individuals with FH can be treated with drugs that result in increased production of LDL receptors in liver cells. Which of the following best explains the observation that the drugs can effectively control blood cholesterol levels in individuals who are heterozygous but are not effective in individuals homozygous for the mutant allele? A The drugs repair the mutant allele by copying the wild-type allele. B The drugs prevent cholesterol from entering the liver cells in individuals who are heterozygous but not in individuals who are homozygous for the mutant allele. C Cholesterol molecules primarily bind to HDL receptors in individuals with FH. D There must be at least one copy of the wild-type LDL receptor allele to produce functional LDL receptors.

D There must be at least one copy of the wild-type LDL receptor allele to produce functional LDL receptors.

Precise regulation of specific hormone levels is required for optimal sperm production in mammals, as summarized in the figure above. Anabolic-androgenic steroids (AAS) are synthetic variants of testosterone that are sometimes abused by persons who desire to enhance their athletic performance or alter their physique. Assuming that AAS function in the same way as naturally occurring testosterone, it is most likely that long-term abuse of AAS would A stimulate FSH secretion B stimulate testosterone production C stimulate LH secretion D reduce sperm production

D reduce sperm production

The figure above shows a model of a ligand precursor being cleaved to produce an active ligand that binds to a specific receptor. Which of the following is most likely to reduce the binding of the active ligand to its receptor? A. A change in the cytoskeletal attachment of transmembrane proteins B. The presence of a large amount of the precursor form of the ligand C. An increase in the ratio of the number of unsaturated to the number of saturated fatty acid tails of the membrane lipids D. A mutation in the receptor gene that causes a substitution of a charged amino acid for a nonpolar amino acid in the ligand binding site of the receptor

D. A mutation in the receptor gene that causes a substitution of a charged amino acid for a nonpolar amino acid in the ligand binding site of the receptor

Researchers investigating the regulation of neurotransmitter release from presynaptic neurons proposed a model (Figure 1) in which CDK5, a protein expressed in axon terminals, inhibits the movement of synaptic vesicles to the presynaptic membrane. To test their model, the researchers used a modified version of green fluorescent protein (GFP*). In slightly alkaline conditions, GFP* exhibits a bright green fluorescence. In acidic conditions, GFP* exhibits no fluorescence. Using standard techniques, the gene encoding is easily introduced into living cells. By engineering the expression of GFP* in laboratory-cultured nerve cells, the researchers found that a bright green fluorescence was exhibited only when a presynaptic neuron was given a certain stimulus. Which of the following observations best supports the hypothesis that negatively regulates neurotransmitter release? A. Introduction of CDK5 protein into neurons results in the movement of synaptic vesicles to the plasma membrane in the absence of any stimulus. B. Uptake of a gene encoding CDK5 by neurons results in the movement of synaptic vesicles to the plasma membrane in the absence of any stimulus. C. Suppression of CDK5 expression in neurons inhibits the movement of synaptic vesicles to the plasma membrane in response to a specific stimulus. D. Inhibition of CDK5 activity in neurons increases the movement of synaptic vesicles to the plasma membrane in response to a specific stimulus.

D. Inhibition of CDK5 activity in neurons increases the movement of synaptic vesicles to the plasma membrane in response to a specific stimulus.

Thyroxin is a hormone that increases metabolic activities within various tissue targets. Low levels of circulating thyroxin trigger the secretion of thyroid-stimulating hormone (TSH) from the anterior pituitary. TSH secretion then stimulates thyroxin production and release by the thyroid gland. The increased level of circulating thyroxin inhibits further secretion of TSH from the anterior pituitary. Based on the information provided, which of the following can most likely be concluded about the TSH-thyroxin loop? A. A person taking thyroxin to supplement low thyroxin secretion will produce more TSH. B. Increased thyroxin production would cause elevated ribosomal activity in the anterior pituitary. C. The structure of the loop would lead to elevated thyroid and tissue activity due to positive feedback. D. The feedback mechanism would maintain relatively constant levels of thyroxin throughout tissue targets.

D. The feedback mechanism would maintain relatively constant levels of thyroxin throughout tissue targets.

In response to elevated blood glucose levels, beta (β) cells in the pancreas release insulin, a regulatory hormone. Insulin signals body cells to take up glucose from the blood, which returns blood glucose levels back to normal. Type 1 diabetes is an autoimmune disorder that destroys β-cells, resulting in elevated blood glucose levels. Researchers have proposed that diabetes could be treated by implanting human embryonic stem cells (hESCs) that have been induced to develop into β-cells (hESC-β). To test the proposed treatment, the researchers set up two groups of genetically identical mice and implanted the mice from one group with hESC-β cells. Several weeks after the hESC-β implant, both groups of mice were given a drug (STZ) that selectively destroys the naturally occurring mouse β-cells but does not affect the implanted hESC-β cells. Figure 1 shows a comparison of average blood glucose levels in both groups of mice. A. The mouse with an hESC-β implant demonstrated a decrease in blood glucose levels for the duration of the experiment. B. The mouse with an hESC-β implant demonstrated an increase in blood glucose levels before STZ treatment. C. The mouse with an hESC-β implant successfully regulated blood glucose levels by regenerating its naturally occurring β-cells. D. The mouse with an hESC-β implant successfully regulated blood glucose levels after STZ treatment but not after the implant was removed.

D. The mouse with an hESC-β implant successfully regulated blood glucose levels after STZ treatment but not after the implant was removed.

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

Distributing replicated chromosomes to daughter nuclei

Cytokinesis

Division of the cytoplasm during cell division

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. Figure 1. Simplified model of clotting cascade 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.

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 KK is required for the formation of the active form of several of the clotting factors, including Factor XX. 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 KK-dependent clotting factors. Based on the model, which of the following best predicts the effects of warfarin on a patient?

Factor XX will not be activated, which will prevent thrombin from forming. Vitamin KK 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. Figure 1. A simplified model of the epinephrine signaling pathway in muscle cells 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.

he 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. Figure 1. A simplified model of the epinephrine signaling pathway in muscle cells 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.

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 SRY gene is absent or nonfunctional, the embryo will exhibit female sexual development.

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 SRYSRY 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.

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. Figure 1. A simplified model of the epinephrine signaling pathway in muscle cells Based on Figure 1, which of the following statements best describes the epinephrine signaling pathway?

In involves enzymes activating other enzymes.

In response to low blood pH, the pH sensors send a signal to the brain, which then sends a signal to the diaphragm, resulting in an increased rate of breathing to help eliminate excess blood CO2 .

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.

The epidermal growth factor receptor EGFREGFR is a cell surface receptor. When a growth factor binds to EGFREGFR, the receptor is activated. The activated EGFREGFR 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 EGFREGFR 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. Figure 1. A simplified model of the epinephrine signaling pathway in muscle cells 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.

Metformin is a drug used to treat type 2 diabetes by decreasing glucose production in the liver. AMPAMP-activated protein kinase (AMPK)(AMPK) is a major cellular regulator of glucose metabolism. Metformin activates AMPKAMPK in liver cells but cannot cross the plasma membrane. By blocking AMPKAMPK with an inhibitor, researchers found that AMPKAMPK 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 AMPKAMPK. Correct. 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.

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.

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. Figure 1. Model of erythrocyte production control 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.

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. Figure 1. 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.

Phosphofructokinase (PFK)(PFK) is a key enzyme in glycolysis. ATPATP is one of the two substrates for the reaction catalyzed by PFKPFK. ATPATP is also an allosteric regulator of PFKPFK. Figure 1 shows the enzyme-substrate interactions of PFKPFK. Figure 1. The enzyme-substrate interactions of PFKPFK A researcher found a mutation that resulted in the PFKPFK enzyme being unable to bind ATPATP 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.

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. Figure 1. A simplified model of the epinephrine signaling pathway in muscle cells 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.

How is plant cell cytokinesis different from animal cell cytokinesis?

Plant cells deposit vesicles containing cell wall building blocks on the metaphase plate; animal cells form a cleavage furrow.

The tumor suppressor protein p53p53 binds to DNA and activates target genes, which results in the synthesis of p21p21, CD95CD95, and other proteins. The p21p21 protein promotes cell-cycle arrest, whereas the CD95CD95 protein promotes apoptosis. Which of the following will most likely result from a loss of p53p53 function?

Rapid cell growth without cell division A loss of p53p53 function will result in unregulated cell proliferation because the p21p21 protein will not be synthesized. In the absence of the p21p21 protein, a cell will continue to progress through the cell cycle without stopping.

DNA replication occurs

S phase

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. Table 1. Number of normal and infected cells found in three phases of the cell cycle Phase of Cell CycleUntreated Cells (n=200n=200)Virus-Infected Cells (n=200n=200)G0G019610Interphase240Mitosis2150 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

The receptors for steroid hormones are located inside the cell instead of the membrane surface like most other signal receptors. How do steroids gain access to their receptors?

Steroid hormones are hydrophobic, so they can readily diffuse through the lipid bilayer of the cell membrane.

The relative amounts of DNADNA present in the nucleus of a cell at four different stages of the life cycle are shown in Figure 1. Figure 1. Relative amounts of DNADNA present in the nucleus of a cell Based on Figure 1, 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 IIII. Stage IIII represents the SS (synthesis) phase of interphase. The genetic information (DNADNA) 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.

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.

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. Figure 1. A simplified model of the glucocorticoid receptor signaling pathway 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 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 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.

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. Figure 1. A simplified model of the epinephrine signaling pathway in muscle cells 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.

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

The irreversible association of FGFR proteins

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

Which of the following best explains how small molecules move between adjacent cells in a plant shoot?

The molecules pass freely through plasmodesmata, which are cytoplasmic strands connecting two cells.

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. Figure 1. A simplified model of thrombin's role in regulating the coagulation cascade 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.

The rate of glycogen synthesis in the cell will increase.

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. Figure 1. A simplified model of the signal transduction cascade triggered by epinephrine binding to the beta-2 adrenergic receptor 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 GLUT4GLUT4, 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.

Trypsinogen is split by the enzyme enterokinase to form an activated molecule of the protease trypsin. Which of the following would confirm that the activation of trypsin is an example of how a positive feedback mechanism can amplify a biological process?

The trypsin produced by the reaction is capable of splitting and activating additional trypsinogen molecules.

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.

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 G1G1/SS 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 DNADNA (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 DNADNA in picograms per cell over several rounds of cell division is shown in Figure 1. Figure 1. Amount of DNADNA in picograms per cell over several rounds of cell division Which of the following statements is consistent with the data in Figure 1?

There is a change from 3 to 6 picograms of DNADNA because DNADNA is replicated before each round of cell division. The change from 3 to 6 picograms of DNADNA prior to replication indicates that the DNADNA has been replicated. The replicated DNADNA 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.

There must be at least one copy of the wild-type LDL receptor allele to produce functional LDL receptors.

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.

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.

What is a primary function of transcription factors?

They control gene expression to help produce proteins.

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

Consider this pathway: epinephrine → G protein-coupled receptor → G protein → adenylyl cyclase → cAMP The activated enzyme in this pathway is ________.

adenylyl cyclase

In the formation of biofilms, such as those forming on unbrushed teeth, cell signaling serves which function?

aggregation of bacteria that can cause cavities

The metaphase stage of mitosis is characterized by ___.

alignment of chromosomes in the cell

In the cells of many eukaryotic species, the nuclear envelope has to disappear to permit which of the following events in the cell cycle?

attachment of microtubules to kinetochores

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.

GG 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 GG protein, the GG protein is activated. The GG protein then activates an enzyme that produces a second messenger called cAMPcAMP. Which of the following describes a critical role of cAMPcAMP during the transduction stage of a GG protein signal transduction pathway?

cAMP results in the activation of an enzyme that amplifies the signal by acting on many substrate molecules. Typically, cAMPcAMP 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.

Consider this pathway: epinephrine → G protein-coupled receptor → G protein → adenylyl cyclase → cAMP The second messenger in this pathway is ________.

cyclic AMP

What two components constitute an active MPF that builds in concentration to trigger the cell's passage past the G2 checkpoint into mitosis?

cyclin and CDK

Consider this pathway: epinephrine → G protein-coupled receptor → G protein → adenylyl cyclase → cAMP The ligand in this pathway is ________.

epinephrine

The relative amount of DNA in a cell at various stages of the cell cycle is shown in Figure 1 . Figure 1. Amount of DNA per cell during different stages of the cell cycle, relative to the beginning of the G1 stage Which of the following best describes how the amount of DNA in the cell changes during M phase?

he amount of DNADNA is halved as the cell divides into two daughter cells.

Scientists isolate cells in various phases of the cell cycle. They isolate a group of cells that have 50% more DNA than G1 phase cells. What is the most likely part of the cell cycle from which these cells were isolated?

in the S phase of the cell cycle

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.

Binding of a signaling molecule to which type of receptor leads directly to a change in the distribution of ions on opposite sides of the membrane?

ligand-gated ion channel

medication enters the target cell and inhibits an enzyme that normally synthesizes a second messenger.

G1 phase of the cell cycle is associated with which of the following cellular events?

normal growth and cell function

Lipid-soluble signaling molecules, such as testosterone, cross the membranes of all cells but affect only target cells because

only target cells have intracellular receptors present to receive the signal.

Telophase

phase of mitosis in which the distinct individual chromosomes begin to spread out into a tangle of chromatin

A signal transmitted via a series of activated proteins is generally associated with which of the following events?

phosphorylation to activate each protein in the series

Apoptosis

programmed cell death

At which phase of the cell cycle do centrioles begin to move apart in animal cells?

prophase

The mitotic spindle plays a critical role in which of the following processes?

separation of sister chromatids

Anaphase

the third phase of mitosis, during which the chromosome pairs separate and move toward opposite poles

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