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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?
a.Chemicals that are secreted from antigen-presenting cells then activate helper T cells.
b.A macrophage cell engulfs a pathogen in the blood.
c.Antigens attaching to receptors on memory B cells stimulate the memory B cells to become plasma cells.
d.Antigen-presenting cells engulf antigens at the first exposure.
a.Chemicals that are secreted from antigen-presenting cells then activate helper T cells.
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 explains a primary function of plasmodesmata?
a. They allow the movement of molecules from one cell to another, enabling communication between cells.
b. They prevent the cell membrane from pulling away from the cell wall during periods of drought.
c.They eliminate the need to produce signaling molecules and eliminate the need for cells to have receptors for signaling molecules.
d.They increase the surface area available for attachment of ribosomes and thus increase protein synthesis.
a. They allow the movement of molecules from one cell to another, enabling communication between cells.
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?
A.The hormone interacts with the nerves at the base of the brain and directs signals to the target cells through the nervous system.
B.The hormone diffuses into target cells adjacent to the anterior pituitary gland, where the hormone is degraded.
C.The hormone is released into the bloodstream where it can be transported to all cells with the correct receptors.
D.The hormone moves through cytoplasmic connections between cells until it has reached all cells with the correct intracellular binding sites.
C.The hormone is released into the bloodstream where it can be transported to all cells with the correct receptors.
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?
A. cAMP carries the signal to the nucleus of the cell and results in new sequences of nucleotides being added to the cell’s DNA.
B. cAMP binds the extracellular signal molecule and carries it to the intracellular target specified by the signal.
C. cAMP modifies a specific monomer so that it can be added to an elongating structural macromolecule.
D. cAMP results in the activation of an enzyme that amplifies the signal by acting on many substrate molecules.
D. cAMP results in the activation of an enzyme that amplifies the signal by acting on many substrate molecules.
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.
Which of the following best describes the component that metformin represents in a signal transduction pathway that regulates glucose production in the liver?
A. It is a secondary messenger that amplifies a signal through a cascade reaction.
B. It is a ligand that activates the signal transduction pathway of the activation of AMPK.
C. It is an allosteric regulator that binds to a crucial section of the DNA that makes the enzymes needed for glucose uptake.
D. It is a competitive inhibitor that binds to glucose and prevents it from entering the cell.
B. It is a ligand that activates the signal transduction pathway of the activation of AMPK.
Which of the following steps in a signaling pathway typically occurs first once a chemical messenger reaches a target cell?
A. Specific genes are activated.
B. A second messenger molecule is produced.
C. A ligand binds to a receptor.
D. Specific proteins are synthesized.
C. A ligand binds to a receptor.
Which of the following justifies the claim that differences in components of cell signaling pathways explain the different responses to epinephrine?
A. 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.
B. Cell signaling depends on the transduction of a received signal by the nervous system. Not all cells are close enough to a synapse to receive the signal and respond.
C. Cell signaling depends on the signal being able to diffuse through the cell membrane. Epinephrine is incapable of diffusing through some plasma membranes because of the membrane’s phospholipid composition.
D. Cell signaling requires reception, transduction, and response. All cells can receive epinephrine, all cells respond with a pathway, but only select cells have the proper coding in their DNA to respond.
A. 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.
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?
A. If the SRY gene is absent or nonfunctional, the embryo will exhibit male sexual development.
B. If the SRY gene is absent or nonfunctional, the embryo will exhibit female sexual development.
C. An embryo with a male sex chromosome will always exhibit male sexual development.
D. An embryo with two male sex chromosomes will always exhibit male sexual development.
B. If the SRY gene is absent or nonfunctional, the embryo will exhibit female sexual development.
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.
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?
A. An experiment showed that a mutation in the ced−9 gene led to excessive cell death in C. elegans.
B. An experiment showed that the ced−9 gene normally produces a protein that promotes excessive cell death in C. elegans.
C. A mutation in ced−3 will cause ced−9 to be incorrectly transcribed.
D. Apoptosis is dependent on a signal from the ced−9 gene in C. elegans.
A. An experiment showed that a mutation in the ced−9 gene led to excessive cell death in C. elegans.
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.
Which of the following statements best predicts the effect of a loss of function of the insulin receptor’s intracellular domain?
A. The stimulation of the signal transduction pathway will increase.
B. The storage of GLUT4 in vesicles inside the cell will increase.
C. The number of GLUT4 molecules in the plasma membrane will increase.
D. The concentration of glucose inside the cell will increase.
B. The storage of GLUT4 in vesicles inside 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.
Which of the following outcomes will most likely result from the inactivation of the beta-2 adrenergic receptor?
A. The cellular concentration of cyclic AMP will increase.
B. The enzymatic activity of protein kinase A will increase.
C. The activation of glycogen phosphorylase will increase.
D.The rate of glycogen synthesis in the cell will increase
D.The rate of glycogen synthesis in the cell 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.
Which of the following changes in the FGFR signaling pathway is most likely to result in uncontrolled cell proliferation?
A. The irreversible association of FGFR proteins
B. The loss of the FGFR protein kinase function
C. A decrease in the intracellular concentration of ATP
D. A decrease in the extracellular concentrations of fibroblast growth factors
A. The irreversible association of FGFR proteins
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?
A.The activity of the enzyme will not be affected because the active site is not involved in substrate binding at the allosteric site.
B. Negative feedback regulation does not occur, so the enzyme will be active when glycolysis is not needed.
C. Positive feedback does not occur, and the activity of the enzyme will decrease when glycolysis is needed.
D. The activity of the enzyme will fluctuate independent of the ATP concentration.
B. Negative feedback regulation does not occur, so the enzyme will be active when glycolysis is not needed.
A person’s blood glucose level fluctuates during the day,. 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.?
A.Immediately after the meal, the blood glucose level will decrease because of the increase in glucagon levels.
B.Immediately after the meal, the blood glucose level will increase, and then insulin will be secreted to counter the increase.
C.Several hours after the meal, the blood glucose level will increase sharply because of an increase in the amount of glucagon secreted.
D.The blood glucose level will not change after the 5 p.m. meal because the person has already consumed two meals
B.Immediately after the meal, the blood glucose level will increase, and then insulin will be secreted to counter the increase.
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. Warfarin is a drug used to treat certain blood clots. . Based on the model, which of the following best predicts the effects of warfarin on a patient?
A. Fibrinogen will form fibrin, but the clot will not form because Factor XIII will not be synthesized.
B. The intrinsic pathway will take over because the clotting factors are part of that pathway.
C.Thrombin will be converted to prothrombin because Factor X will reverse the reaction.
D.Factor X will not be activated, which will prevent thrombin from forming.
D.Factor X will not be activated, which will prevent thrombin from forming.
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?
A. 5 percent
B. 10 percent
C. 25 percent
D. 50 percent
C. 25 percent
Researchers grew seedlings of corn, Zea mays, in loose and 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?
A. The cells of the root tips grow to larger sizes when the seedlings are planted in compact sand than when the seedlings are planted in loose sand.
B. The average rate of mitotic cell division is greater for the root tips growing in loose sand than for the root tips growing in compact sand.
C. The average cell cycle time is greater for the root tips growing in compact sand than for the root tips growing in loose sand.
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.
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.
The relative amounts of DNA present in the nucleus of a cell at four different stages of the life cycle are shown in Figure 1.
Based on Figure 1, which of the following statements correctly links a stage of the cell cycle with the event occurring at that stage?
A. Stage I represents the G2 phase of the cell cycle.
B. Synthesis of sufficient DNA for two daughter cells occurs in stage II.
C. Stage III includes mitosis.
D. The replication of genetic material occurs in stage IV.
B. Synthesis of sufficient DNA for two daughter cells occurs in stage II.
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?
A. The cells have a haploid chromosome number of 3.
B. The cells have a diploid chromosome number of 6.
C. There is a change from 3 to 6 picograms of DNA because DNA is replicated before each round of cell division.
D. There is a change from 6 to 3 picograms of DNA after each cell division because the chromosomes lengthen following cell division.
C. There is a change from 3 to 6 picograms of DNA because DNA is replicated before each round of cell division
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.
Which of the following most accurately describes an observation and an effect of the viral infection indicated by the data in Table 1?
A. Normal cells spend 98 percent of their time cycling in and out of interphase. The virus reduces this to 5 percent of the time.
B. Twenty percent of the virus-infected cells are in interphase. These cells are no longer part of the cell cycle.
C. Forty percent of the virus-infected cells are in interphase. These cells are preparing for replication of genetic material.
D. Seventy-five percent of the virus-infected cells are found in mitosis. The virus stimulates frequent cell division.
D. Seventy-five percent of the virus-infected cells are found in mitosis. The virus stimulates frequent cell division.
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?
A. 5%
B. 11%
C. 18%
D.66%
C. 18%
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?
A. Increased apoptosis will lead to abnormal growth of the tissue.
B. Increased cell division will lead to the formation of a tumor.
C. Cells will exit the cell cycle, entering a non-dividing G0 phase.
D. Fewer cells will be in any of the stages of mitosis.
B. Increased cell division will lead to the formation of a tumor.
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?
A. Rapid cell growth without cell division
B. Immediate activation of apoptosis pathways
C. Uncontrolled cell proliferation
D. Increased expression of p53 target genes
C. Uncontrolled cell proliferation
Which statement best predicts why a cell’s progression through the cell cycle might be halted at the G1/S checkpoint?
A. Spindle fibers have not correctly attached to chromosomes.
B. There are not enough nucleotides available to construct new DNA.
C. Damage occurred to DNA when it was being copied in G1.
D. Proteins necessary for M phase of the cell cycle have not been produced.
B. There are not enough nucleotides available to construct new DNA.
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?
A. The proteins receive electrical signals from nerve cells.
B. The proteins leave the cell and travel in the bloodstream to other cells.
C. The proteins interact directly with proteins on the surfaces of other cells.
D. The proteins bind to molecules secreted by cells located in other parts of the body.
C. The proteins interact directly with proteins on the surfaces of other cells.
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.
Which of the following statements best explains Delta’s role in regulating cell communication through the Notch signaling pathway?
A. Delta transmits a chemical signal to all the cells of a developing embryo.
B. Delta allows the cells of a developing embryo to communicate without making direct contact.
C. Delta restricts cell communication to short distances within a developing embryo.
D. Delta determines which cells in a developing embryo express the gene that encodes the Notch protein.
C. Delta restricts cell communication to short distances within a developing embryo.
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?
A. Membrane-bound organelles
B. Condensed, duplicated chromosomes
C. Branched polysaccharides
D. Small, water-soluble molecules
D. Small, water-soluble molecules
The relative amount of DNA in a cell at various stages of the cell cycle is shown in Figure 1 .
Which of the following best describes how the amount of DNA in the cell changes during M phase?
A. The amount of DNA doubles as the DNA is replicated.
B. The amount of DNA slightly increases as a result of new organelle synthesis.
C. The amount of DNA does not change while the cell grows.
D. The amount of DNA is halved as the cell divides into two daughter cell
D. The amount of DNA is halved as the cell divides into two daughter cell
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?
A. Mutant 1 cells are more similar to mutant 3 cells than to wild-type cells.
B. In wild-type cells, the percent of cells in anaphase is twice the amount of those in telophase
C. In mutant 3 cells, more time is spent in prophase/prometaphase than in the later stages of mitosis.
D. The percent of mutant 2 cells in anaphase is higher than that of mutant 1 cells.
C. In mutant 3 cells, more time is spent in prophase/prometaphase than in the later stages of mitosis.
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?
A. −100%
B. −50%
C. +50%
D. +100%
D. +100%
Which of the following presents a correct interpretation of the changes in chromosome number depicted in Figure 1 ?
A. DNA replication occurs between metaphase and anaphase, doubling the number of chromosomes. Between telophase and cytokinesis, the cell divides in two, with each cell receiving half of the replicated chromosomes.
B. New chromosomes formed during prophase are doubled during anaphase and are recombined before cytokinesis.
C. 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.
D. At anaphase a cell contains two identical copies of each chromosome, but following telophase, one of the copies is broken down into nucleotides.
C. 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.
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?
A.5%
B.35%
C.50%
D.95%
D.95%
A group of researchers cultured yeast cells in a nutrient-rich environment and a nutrient-poor environment and observed the duration of the stages of their cell cycles. The results of their study are summarized in Table 1.
The cell cycle of yeast cells grown in the nutrient-poor environment is approximately what percent of the cell cycle of yeast cells grown in the nutrient-rich environment?
A.168
B.127
C.179
D.160
A.168
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?
A. The intracellular concentration of glycogen will increase.
B. The intracellular concentration of activated protein kinase A will increase.
C. The intracellular concentration of cyclic AMP will increase.
D. The intracellular concentration of glucose-1-phosphate will increase.
A. The intracellular concentration of glycogen will increase.
Glucocorticoids are steroid hormones that control cellular responses through several different signaling pathways. One of the signaling pathways involves the glucocorticoid receptor, an intracellular protein that is activated by binding to a glucocorticoid molecule. A simplified model of the glucocorticoid receptor signaling pathway is represented in Figure 1.
Which of the following statements best predicts the effect of a mutation that results in a loss of the glucocorticoid receptor’s ligand binding function?
A. The transduction of the glucocorticoid signal across the plasma membrane will be blocked.
B. The glucocorticoid receptor will remain associated with the accessory proteins.
C. The rate of diffusion of glucocorticoid molecules into the cell will increase.
D. The concentration of glucocorticoid receptors inside the nucleus will increase
B. The glucocorticoid receptor will remain associated with the accessory proteins.
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?
A. Production of activated molecule 1 will stop, but production of activated molecules 2 and 3 will continue.
B. The molecule that normally binds to protein A will no longer attach, deactivating the cellular response.
C. The molecule that normally binds to protein A will not enter the cell, thus no cellular response will occur.
D. Since protein A is embedded in the membrane, the mutation will be silent and not affect the cellular response.
B. The molecule that normally binds to protein A will no longer attach, deactivating the cellular response.
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?
A. The concentration of cyclic AMP will decrease because adenylyl cyclase will no longer be activated.
B. The G protein will diffuse out of the cell because it will no longer bind to the plasma membrane.
C. Phosphorylase kinase will remain active because protein kinase A will no longer be deactivated.
D. Glycolysis will stop because epinephrine signaling will no longer stimulate glycogen breakdown.
C. Phosphorylase kinase will remain active because protein kinase A will no longer be deactivated.
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?
A. More erythropoietin will be secreted from the kidneys, decreasing production of erythrocytes.
B. More erythropoietin will be secreted from the kidneys, increasing production of erythrocytes.
C. Less erythropoietin will be secreted from the kidneys, decreasing production of erythrocytes.
D. Less erythropoietin will be secreted from the kidneys, increasing production of erythrocytes.
B. More erythropoietin will be secreted from the kidneys, increasing production of erythrocytes.
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?
A. The activation of clotting factors will be blocked.
B. The rate of fibrin formation will decrease.
C. Thrombin will be converted to prothrombin.
D. The rate of blood clot formation will increase.
B. The rate of fibrin formation will 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?
A. It involves the opening and closing of ion channels.
B. In involves enzymes activating other enzymes.
C. It involves changes in the expression of target genes.
D. It involves protons moving down a concentration gradie
B. In involves enzymes activating other enzymes.
Which of the following statements best describes the role of adenylyl cyclase in the epinephrine signaling pathway?
A. It converts a polymer to its monomer subunits.
B. It moves substances across the plasma membrane.
C. It accelerates the production of a second messenger.
D. It transfers phosphate groups from ATP to protein substrates.
C. It accelerates the production of a second messenger.
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?
A. It acts as a signaling molecule that passes the signal from the cell to other cells.
B. It acts as a receptor that carries the signal from outside the cell to inside the cell.
C. It acts as a second messenger that helps relay and amplify the signal within the cell.
D. It acts as a channel protein that transmits the signal across the cell’s nuclear membrane.
C. It acts as a second messenger that helps relay and amplify the signal within the cell.
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?
A. Cells with inactive GSK3β fail to trigger apoptosis.
B. Cells with inactive GSK3β fail to proceed past the G2/M checkpoint.
C. Cells with overactive GSK3β are more likely to repair DNA damage.
D. Cells with overactive GSK3β have longer cell cycl
A. Cells with inactive GSK3β fail to trigger apoptosis.
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?
A. The environment already contains cancer cells.
B. The environment has an abundance of nutrients.
C. The environment lacks signals that would otherwise tell the cell to stop dividing.
D.The environment contains mutagens that induce mutations that affect cell-cycle regulator proteins.
D.The environment contains mutagens that induce mutations that affect cell-cycle regulator proteins.
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?
A. The yeast cells will transition out of G0 but will fail to complete the G1 phase.
B. The yeast cells will initiate mitosis but will fail to complete the G2 phase.
C. The yeast cells will replicate their chromosomes but will fail to complete cytokinesis.
D. The yeast cells will replicate their organelles but will fail to complete the S phase.
C. The yeast cells will replicate their chromosomes but will fail to complete cytokinesis.
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?
A. Epinephrine is a signaling molecule that binds to a transmembrane protein.
B. The G protein in the epinephrine signaling pathway consists of three different subunits.
C. Phosphorylase kinase catalyzes the hydrolysis of ATP.
D. Glycogen phosphorylase catalyzes the conversion of glycogen to glucose-1-phosphate.
D. Glycogen phosphorylase catalyzes the conversion of glycogen to glucose-1-phosphate.
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?
A. Ethylene is a simple gaseous molecule, which makes it easily detected by receptors.
B. Fruit will ripen in closed containers without exposure to air.
C. Ethylene synthesis is under both positive and negative feedback regulation.
D. Loss-of-function mutations in ethylene receptors result in changes to the ripening process.
D. Loss-of-function mutations in ethylene receptors result in changes to the ripening process.
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 SRY gene produces a protein that binds to specific regions of DNA in certain tissues, which affects the development of these tissues.
B. The SRY gene produces a protein that deletes portions of the X chromosome in males so that male characteristics can develop.
C. The SRY gene produces an RNA segment that is exported from specific cells and targets the developing gonads.
D. The SRY gene is found only in tissues of the developing gonads.
A. The SRY gene produces a protein that binds to specific regions of DNA in certain tissues, which affects the development of these tissues.
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