Chapter 9
91. An increased heart rate caused by the release of adrenaline from the adrenal glands is an example of _____ signaling. A) autocrine B) contact-dependent C) paracrine D) endocrine
D) endocrine
104. How many subunits make up some types of G protein? A) two B) three C) four D) five E) six
B) three
123. Which of the following statements does NOT describe part of the MAP kinase pathway? (Select all that apply.) A) A receptor kinase is activated by binding to a growth factor, resulting in the rapid movement of ions into the cell. B) The activated receptor kinase dimer activates the Ras protein to bind to GTP. C) The activated Ras protein activates protein kinases in the signal transduction pathway. D) A series of protein kinases amplify the signal to the nucleus, where genes responsible for cell division are turned on. E) A phosphatase terminates the cellular response.
A) A receptor kinase is activated by binding to a growth factor, resulting in the rapid movement of ions into the cell.
113. What causes the inactivation of a G protein? A) The alpha subunit catalyzes the hydrolysis of GTP to GDP and inorganic phosphate. B) The beta and gamma subunits trigger the hydrolysis of GTP to GDP. C) A phosphatase removes the inorganic phosphate group from GTP. D) The inactive receptor catalyzes the replacement of GTP by GDP.
A) The alpha subunit catalyzes the hydrolysis of GTP to GDP and inorganic phosphate.
134. You are a medical student working in a cancer research laboratory. Your boss has given you samples of cancer cells and blood from a patient. She has told you that the cells have no mutations in any of their signaling molecule proteins (that is, all the proteins are normal), but that the cells' signaling transduction properties are not normal, causing them to be cancerous. Which of the following could account for the increased cell proliferation in the patient? (Select all that apply.) A) The cells taken from the patient have more growth factor receptors than normal. B) The concentration of a signaling molecule in the patient is higher than usual. C) The cells taken from the patient exhibit a reduced level of signal amplification. D) None of the other answer options is correct.
A) The cells taken from the patient have more growth factor receptors than normal. B) The concentration of a signaling molecule in the patient is higher than usual.
119. Phosphatases are a family of enzymes that remove phosphate groups from specific proteins; these phosphate groups had been added to the proteins by protein kinases. Vanadate is an inhibitor of phosphatases in eukaryotic cells. What effect would vanadate have on the response of cells to signals received by receptor kinases? A) The response of the cell would last longer than it normally would. B) The response of the cell would be shorter than it normally would. C) The signal would still bind the receptor, so there would be no effect.
A) The response of the cell would last longer than it normally would.
141. Cancer is a disease of cell division. A) True B) False
A) True
137. What is the end result of activating the MAP kinase pathway? A) a change in gene expression B) phosphorylation of multiple cytosolic proteins C) synthesis of second messenger molecules D) ion flow
A) a change in gene expression
125. Complexity in cell communication from molecular cross talk can be due to: (Select all that apply.) A) inhibition of one signaling pathway by a component of another signaling pathway. B) an intersection of two signaling pathways that allow two signals to enhance the cellular response. C) signaling molecules interacting with each other before binding the receptor. D) None of the other answer options is correct.
A) inhibition of one signaling pathway by a component of another signaling pathway. B) an intersection of two signaling pathways that allow two signals to enhance the cellular response.
107. Cyclic AMP (cAMP) is an example of a(n): A) second messenger. B) ligand. C) effector or target protein. D) G protein.
A) second messenger.
105. GTP binding occurs on which subunit of a G protein? A) the alpha subunit B) the beta subunit C) the gamma subunit D) GTP binds both beta and gamma subunits.
A) the alpha subunit
146. Ras is most similar to: A) the alpha subunit of three-subunit G proteins. B) the beta subunit of three-subunit G proteins. C) the gamma subunit of three-subunit G proteins. D) receptor kinases. E) ion channels.
A) the alpha subunit of three-subunit G proteins.
148. A given cell usually only has one signaling pathway. A) True B) False
B) False
114. How is a G protein classified? A) It is a transmembrane protein. B) It is a peripheral membrane protein. C) It is an integral membrane protein. D) It is a second messenger.
B) It is a peripheral membrane protein.
133. A number of mutations have been described in G proteins, such as Ras, that have profound effects on their activity. For example, some mutations greatly increase the affinity of the G protein for GDP, making it very difficult for GDP to be exchanged for GTP. Other mutations prevent the hydrolysis of GTP to GDP. Which of the following scenarios would still result in a proliferation signal via the kinase cascade in the absence of ligand binding to its receptor kinase? A) a continuously active receptor and an inactive Map kinase pathway B) a Ras molecule that has no GTPase activity C) a continuously inactive MAP kinase pathway and an inactive Ras protein D) a continuously active Ras protein and an inactive MAP kinase pathway E) a continuously activated receptor in the absence of ligand
B) a Ras molecule that has no GTPase activity
139. What is one of the possible cellular responses following activation of the MAP kinase pathway? A) the formation of second messengers in the cytosol B) a change in gene expression resulting in cell division C) the activation of adenylyl cyclase D) both the activation of adenylyl cyclase and the formation of second messengers
B) a change in gene expression resulting in cell division
145. PDGF binds to: A) a G protein-coupled receptor. B) a receptor kinase. C) an ion channel.
B) a receptor kinase.
112. Signal amplification relies on: A) increasing amounts of ligand as signal transduction proceeds. B) a sequential increase in the different components of the signal transduction pathway. C) increasing numbers of cell-surface receptors as the signal is transduced. D) increased activity of protein phosphatases.
B) a sequential increase in the different components of the signal transduction pathway.
117. G protein-coupled receptors: A) are only present in humans. B) are widespread and have diverse effects. C) are ion channels. D) become phosphorylated on binding a signaling molecule. E) All of these choices are correct.
B) are widespread and have diverse effects.
144. The FIRST step following PDGF binding of the receptor is: A) phosphorylation. B) dimerization. C) activation of MAP kinase. D) activation of gene expression.
B) dimerization.
147. The presence of excess EGF receptors can result in: A) diminished cell division. B) excessive cell division. C) normal cell division.
B) excessive cell division.
120. Many mutations in receptor kinases that lead to cancer allow the receptor to dimerize and become activated, even in the absence of signaling molecules. An example is a mutant form of the EGF receptor kinase called Her2/neu. An antibody that prevents dimerization of Her2/neu receptor kinases is being tested for its effectiveness in preventing cancer. At which stage does this drug work? A) It prevents the signaling cell from producing the signal. B) It prevents the receptor from binding to the signal. C) It prevents the receptor from becoming activated. D) It prevents the termination of the signal.
C) It prevents the receptor from becoming activated.
132. What would happen to the signaling cascade if phosphatases were nonfunctional? A) It would stop in the absence of ligand. B) It would slow down in the absence of ligand. C) It would continue in the absence of ligand. D) None of the other answer options is correct.
C) It would continue in the absence of ligand.
140. How do mitogen-activated protein (MAP) kinases become inactive? A) Ras hydrolyzes GTP to GDP. B) Ligand diffuses away from the ligand-binding site. C) Phosphatases remove phosphate groups. D) Receptor kinases move apart in the membrane.
C) Phosphatases remove phosphate groups.
135. Why are some mutations of Ras associated with cancer? A) Ras binds to growth factor receptors. B) Ras is a type of second messenger. C) Ras activates the MAP kinase signal transduction pathway. D) Ras alters ion flow across the cell membrane.
C) Ras activates the MAP kinase signal transduction pathway.
130. Why do the functions of many receptor kinases depend on the fluid nature of the plasma membrane? A) The generation of cAMP requires a fluid membrane. B) Binding of ligand to the receptor requires a fluid membrane. C) The receptor monomers must move together and dimerize to be activated. D) Phosphorylation requires a fluid membrane.
C) The receptor monomers must move together and dimerize to be activated.
109. What is the very FIRST effect of ligand binding to a G protein-coupled receptor? A) the activation of an effector protein B) the release of the alpha subunit of the G protein C) a conformational change in the cytoplasmic domain of the receptor D) an exchange of GTP in place of GDP on the alpha subunit of the G protein
C) a conformational change in the cytoplasmic domain of the receptor
121. You are studying a newly discovered growth factor. You find that this growth factor stimulates the proliferation of chicken cells grown in the laboratory. You have also found that the receptor that binds the growth factor is a receptor kinase. Which of the following mutations would you expect to promote uncontrolled cell proliferation? A) a mutation that prevents dimerization of the receptor B) a mutation that destroys the kinase activity of the receptor C) a mutation that inactivates the phosphatase that dephosphorylates the activated receptor D) a mutation that prevents the binding of the normal extracellular signal to the receptor
C) a mutation that inactivates the phosphatase that dephosphorylates the activated receptor
138. Ras is a type of G protein because it: A) triggers the formation of cyclic AMP. B) responds to the activation of G protein-coupled receptors. C) is only active when it binds GTP. D) All of these choices are correct.
C) is only active when it binds GTP.
143. Signaling through receptor kinases: A) only occurs in humans. B) is limited to just a few cell types. C) takes place in most eukaryotic organisms. D) takes place only in prokaryotes.
C) takes place in most eukaryotic organisms.
106. What is the function of adenylyl cyclase? A) to form protein kinase A B) to phosphorylate protein kinase A C) to form cyclic AMP D) to phosphorylate cyclic AMP
C) to form cyclic AMP
111. What happens to the alpha subunit of a G protein with GDP attached? A) It re-assembles with the beta and gamma subunits. B) It no longer activates an effector protein. C) It re-associates with the G protein-coupled receptor. D) All of these choices are correct.
D) All of these choices are correct.
118. Termination is an important step in adrenaline signaling because it: A) prevents an excessive response to adrenaline. B) allows organisms to respond to new stresses. C) allows an appropriate level of response. D) All of these choices are correct.
D) All of these choices are correct.
136. Ligand binding to a receptor kinase results in: A) phosphorylation of the cytoplasmic domain of the receptor. B) binding of cytoplasmic signaling molecules. C) receptor dimerization. D) All of these choices are correct.
D) All of these choices are correct.
149. If two signaling pathways are activated simultaneously: A) they may inhibit each other. B) they may strengthen each other. C) one may inhibit the other. D) All of these choices are correct.
D) All of these choices are correct.
115. The activation of protein kinase A by cyclic AMP binding likely occurs because of: A) the activity of a phosphatase. B) the binding of GTP to protein kinase A. C) the phosphorylation of protein kinase A. D) a conformational change to protein kinase A.
D) a conformational change to protein kinase
108. Inactivation of a cell-surface receptor depends on: A) the binding affinity of the receptor. B) the activity of phosphatases in the cytosol. C) the concentration of ligand surrounding the cell. D) both the binding affinity of the receptor and concentration of ligand surrounding the cell.
D) both the binding affinity of the receptor and concentration of ligand surrounding the cell.
142. Cellular responses that result from receptor kinase activation tend to: A) be short term. B) involve ion channels. C) involve changes in metabolism. D) involve changes in gene expression.
D) involve changes in gene expression.
131. According to Figure 9.14, phosphate groups play a key role in receptor kinase activation by: A) activating the receptor, so that the receptor is capable of binding its signal. B) activating the dimerization of the receptor kinase proteins in the membrane. C) activating receptor kinase activity. D) providing binding sites to recruit and activate signal-transduction proteins. E) All of these choices are correct.
D) providing binding sites to recruit and activate signal-transduction proteins.
110. In order for a G protein to be active: A) the alpha subunit must bind GTP. B) the beta and gamma subunits must separate from the alpha subunit. C) both the beta and gamma subunits must bind GTP. D) the alpha subunit must bind GTP, and the beta and gamma subunits must separate from the alpha subunit.
D) the alpha subunit must bind GTP, and the beta and gamma subunits must separate from the alpha subunit.
116. In the G protein-coupled signal transduction pathway, phosphatases are responsible for the inactivation of: A) the alpha subunit of a G protein. B) protein kinase A. C) adenylyl cyclase. D) the protein target activated by protein kinase A. E) All of these choices are correct.
D) the protein target activated by protein kinase A.
127. The type of cellular response to a signal does NOT depend on: A) the type of receptor being expressed in the cell. B) the type of signal transduction proteins expressed in the cell. C) other signals to which the cell is also responding. D) the type of terminator proteins being expressed in the cell. E) All of these choices are correct.
D) the type of terminator proteins being expressed in the cell.
124. Defects in cell signaling can lead to a cancerous cell as a result of: A) overproduction of signals that trigger cell division. B) overproduction of a receptor that triggers cell division. C) a defective receptor that stays in the activated state and triggers cell division continuously. D) a defective signal transduction protein that stays in the activated state and triggers cell division continuously. E) All of these choices are correct.
E) All of these choices are correct.
126. A cellular response to a signal can be terminated by: A) depletion of the signal that activates the receptor. B) inactivation of intracellular signal transduction proteins. C) inactivation of proteins in the signal pathway over time. D) depletion of a second messenger. E) All of these choices are correct.
E) All of these choices are correct.
18. In cell communication, which one of the following is a requirement of the responding cell? A) It must be a eukaryotic cell. B) It must produce signaling molecules. C) It must have receptor proteins. D) It must be a prokaryotic cell.
C) It must have receptor proteins.
42. Mammalian steroid hormones are signaling molecules that function in which of the following types of cell signaling? A) paracrine B) autocrine C) endocrine D) All of these choices are correct.
C) endocrine
7. Choose from the following terms to fill in the blanks in the CORRECT order. A. ligand B. signaling cell C. receptor D. responding cell In communication between cells, the _____ produces the signaling molecule, also known as the _____; the _____ produces the _____, to which the signaling molecule binds, A) B, A, D, C B) A, B, C, D C) B, C, A, D D) D, C, B, A
A) B, A, D, C
8. Nicotine from cigarette smoke acts as a ligand and associates with specific cells in the nervous system. Nicotine eventually produces feelings of pleasure and well-being. Below are the events that happen in the cellular response to nicotine. Place the events in the correct order to describe the steps in the signaling pathway. A. The acetylcholine receptor is an ion channel, and, when a ligand binds, the ion channel opens. B. An influx of ions carries the signal to the reward areas of the brain. C. Nicotine binds to the transmembrane protein that normally binds the neurotransmitter acetylcholine. D. The signal causes release of dopamine in the brain, which causes good feelings. E. Nicotine is quickly eliminated from the body (causing cravings for more cigarettes to produce good feelings). A) C, A, B, D, E B) A, D, B, C, E C) B, A, C, D, E D) C, D, B, A, E E) Nicotine is quickly eliminated from the body (causing cravings for more cigarettes to produce good feelings).
A) C, A, B, D, E
97. Which type of receptor needs an accessory protein to signal? A) G protein-coupled receptor B) receptor kinase C) ligand-gated ion channel D) None of the other answer options is correct.
A) G protein-coupled receptor
71. Which type of receptor is membrane-associated? (Select all that apply.) A) G protein-coupled receptor B) receptor kinase C) ligand-gated ion channel D) intracellular receptor
A) G protein-coupled receptor B) receptor kinase C) ligand-gated ion channel
72. Which type of receptor undergoes a conformational change upon activation? (Select all that apply.) A) G protein-coupled receptor B) receptor kinase C) ligand-gated ion channel D) intracellular receptor
A) G protein-coupled receptor B) receptor kinase C) ligand-gated ion channel D) intracellular receptor
51. Notch and Delta are both transmembrane proteins involved in cell communication in the developing nervous system of vertebrate animals. What makes Notch different from Delta? A) Notch is a receptor, and Delta is a signaling molecule. B) Notch is a signaling molecule, and Delta is a receptor. C) Notch is required at higher density than Delta to alter cell fate. D) All of these choices are correct.
A) Notch is a receptor, and Delta is a signaling molecule.
96. According to Figure 9.11, which of the following is NOT responsible for amplifying the signal in a cell responding to adrenaline signaling? A) One adrenaline molecule can bind to and activate many receptors simultaneously. B) One molecule of adenylyl cyclase can produce many molecules of cAMP. C) One molecule of protein kinase A can phosphorylate and activate many target proteins. D) One activated receptor can activate many G proteins.
A) One adrenaline molecule can bind to and activate many receptors simultaneously.
1. Which of the following is NOT part of the general response of cells during cellular communication? A) The cell does not return to its normal activities after the signal has exerted its effect. B) Receptors on the outside of the cell bind to specific signal molecules. C) A cell-surface receptor molecule becomes activated by binding to a molecular signal. D) An activated cell-surface receptor transfers the signal to the interior of the cell. E) The signal is transmitted inside the cell and amplified as a series of proteins are activated in sequence, affecting cellular activities according to the type of signal involved.
A) The cell does not return to its normal activities after the signal has exerted its effect.
22. Recall from the text the example of cell communication in Streptococcus pneumoniae: The rate of DNA uptake by pneumococcal cells increases sharply when they are at high density, due to changes in gene expression brought about by signaling between cells. If the pneumococcal cells did not express receptor proteins, how would the rate of DNA uptake be affected when the cells reach high density? A) There would be no change in the rate of DNA uptake. B) There would be a larger than normal increase in the rate of DNA uptake. C) There would be a smaller than normal increase in the rate of DNA uptake. D) There would be a decrease in the rate of DNA uptake.
A) There would be no change in the rate of DNA uptake.
16. Signaling pathways have been conserved in a wide range of organisms. A) True B) False
A) True
76. What is the cell's likely response to ligand binding to a steroid receptor located in the nucleus? A) a change in gene expression B) activation of a kinase C) initiation of a signal transduction pathway D) change in ion transport
A) a change in gene expression
58. Which of the following would NOT be considered a cell-surface receptor? A) a receptor that binds a nonpolar steroid hormone and activates transcription B) a receptor that allows ions to enter the cell when a ligand binds C) a receptor that causes GDP to be exchanged for GTP in a G protein D) a receptor that must form a dimer after binding the ligand to transmit a signal
A) a receptor that binds a nonpolar steroid hormone and activates transcription
67. Which of the following would NOT be considered a cell-surface receptor? A) a receptor that binds a nonpolar steroid hormone and activates transcription B) a receptor that allows ions to enter the cell when a ligand binds C) a receptor that causes GDP to be exchanged for GTP in a G protein D) a receptor that forms a dimer after binding the ligand
A) a receptor that binds a nonpolar steroid hormone and activates transcription
11. A cell that responds to an environmental condition by the release of a chemical is an example of which of the following elements of cellular communication? A) a signaling cell B) a signaling molecule C) a receptor protein D) a responding cell E) None of the other answer options is correct.
A) a signaling cell
73. In the context of cell signaling, to what does the term ligand refer? A) a signaling molecule B) the extracellular domain of a receptor protein C) the proteins activated as part of a signal transduction pathway D) a type of gated channel
A) a signaling molecule
102. Which of the following CORRECTLY pairs enzymes that activate and terminate the same step in a signaling event? (Select all that apply.) A) adenylyl cyclase (activates) and phosphodiesterase (terminates) B) protein kinase (activates) and phosphatase (terminates) C) protein kinase (activates) and phosphodiesterase (terminates) D) adenylyl cyclase (activates) and phosphatase (terminates)
A) adenylyl cyclase (activates) and phosphodiesterase (terminates) B) protein kinase (activates) and phosphatase (terminates)
88. A bacterium releases a toxin that binds to and activates a G protein-coupled receptor in the mammalian gut. The result is high levels of cAMP in these cells. This toxin might work by: A) binding to and activating the G protein-coupled receptor in these cells. B) binding to and inhibiting the G protein-coupled receptor in these cells. C) causing the subunit of the G protein to stay associated with the and subunits. D) causing the subunit of the G protein to bind GDP constantly. E) causing adenylyl cyclase to dissociate from the membrane.
A) binding to and activating the G protein-coupled receptor in these cells.
30. Which type of cell signaling does not rely on the diffusion of a chemical signal molecule? A) contact-dependent B) paracrine C) autocrine D) endocrine E) All of these choices are correct.
A) contact-dependent
38. The differentiation of embryonic stem cells into neurons and glial cells is a consequence of which type of cell signaling? A) contact-dependent B) paracrine C) autocrine D) endocrine E) All of these choices are correct.
A) contact-dependent
92. The high variability of the types of G protein-coupled receptors allows: A) different types of cells to respond to different types of signals. B) different types of signal-transduction pathways to respond to signals. C) a rapid response to cell signals. D) a sensitive response to cell signals. E) All of these choices are correct.
A) different types of cells to respond to different types of signals.
52. Based on the data provided in the two graphs shown in Figure 9.5, which method of culturing resulted in the greatest number of fibroblast cells on day 6? A) fibroblasts cultured with serum B) fibroblasts cultured with platelet proteins C) fibroblasts cultured with plasma D) The same results are obtained whether the fibroblasts are cultured with serum or with platelet proteins.
A) fibroblasts cultured with serum
78. Which type of protein adds a phosphate group to another molecule? A) kinase B) G protein C) phosphatase D) phosphorylase
A) kinase
94. Which of the following terminates a cell-signaling event that is initiated by a G protein-coupled receptor? A) phosphatase activity B) protein kinase activity C) adenylyl cyclase activity D) phosphodiesterase activity E) None of the other answer options is correct.
A) phosphatase activity
24. In many signaling pathways, once a signaling molecule binds to a receptor, the receptor becomes phosphorylated. This initial phosphorylation step BEST demonstrates: A) receptor activation. B) signal transduction. C) cellular response. D) termination. E) either cellular response or signal transduction.
A) receptor activation.
61. Which one of the following would be found bound to the regulatory region of a gene? A) steroid hormone receptor B) MAP kinase C) adenylyl cyclase D) cAMP E) protein kinase A
A) steroid hormone receptor
53. Which of the following signaling molecules would you expect to travel the LONGEST distance in the human body? A) testosterone B) Delta C) PDGF D) neurotransmitters E) Notch
A) testosterone
27. A cell can only respond to signals from other cells, not from the physical environment. A) True B) False
B) False
84. Given that most ligands form covalent bonds with their associated receptors, these complexes are more or less permanent and can only be broken through the hydrolysis of ATP. A) True B) False
B) False
50. Review the experiments by Kohler and Lipton described in Figure 9.5. What is the key difference between blood serum and blood plasma that affects their ability to help fibroblasts grow in culture? A) Serum contains more platelet cells than plasma, and platelet cells promote cell growth. B) Molecules found in serum promote cell growth; these molecules are not found in plasma. C) Plasma contains more platelet cells than serum, and platelet cells inhibit cell growth. D) Molecules found in plasma inhibit cell growth; these molecules are not found in serum.
B) Molecules found in serum promote cell growth; these molecules are not found in plasma.
54. Which of the following statements is FALSE regarding a neurotransmitter? A) Neurotransmitters are typically dispersed over small distances. B) Similar to Delta or Notch, neurotransmitters are usually attached to the cell surface. C) Neurotransmitters can be growth factors. D) Neurotransmitters play a role in muscle contraction. E) Neurotransmitters are produced by neurons.
B) Similar to Delta or Notch, neurotransmitters are usually attached to the cell surface.
95. Which of the following is/are true about G proteins? (Select all that apply.) A) All G proteins associate with G protein-coupled receptors. B) Some G proteins are composed of three subunits. C) G proteins release GDP and bind GTP when associated with an activated receptor. D) G proteins become deactivated when bound GTP is hydrolyzed to GDP. E) All of these choices are correct.
B) Some G proteins are composed of three subunits. C) G proteins release GDP and bind GTP when associated with an activated receptor. D) G proteins become deactivated when bound GTP is hydrolyzed to GDP.
17. During the signal transduction process, the signal often triggers a signal transduction cascade. For example, an activated receptor activates hundreds of protein A. Each activated protein A activates hundreds of protein B and so on until a cellular response occurs. What purpose does this cascade serve? A) Having several intermediates allows for greater control of the response. B) The cascade serves to amplify the signal, so one activated receptor can have a significant response. C) Having a cascade allows the cell to respond to different signals. D) The cascade makes signaling easier to shut off or terminate.
B) The cascade serves to amplify the signal, so one activated receptor can have a significant response. C) Having a cascade allows the cell to respond to different signals.
13. Signal transduction results in: A) a change in the conformation of the receptor protein. B) a response by the cell. C) production of more signal molecules. D) termination of the signal.
B) a response by the cell.
12. A chemical that binds to a cell and causes its activity to change is an example of which of the following elements of cellular communication? A) a signaling cell B) a signaling molecule C) a receptor protein D) a responding cell E) None of the other answer options is correct.
B) a signaling molecule
43. Cell signaling over a long distance is known as _____ signaling. A) paracrine B) endocrine C) contact-dependent D) autocrine
B) endocrine
6. Which is NOT one of the steps in cell signaling? A) signal transduction B) obtaining a high density of signaling molecules C) receptor activation D) signal termination E) cellular response
B) obtaining a high density of signaling molecules
31. Communication between neurons is an example of which type of cell signaling? A) contact-dependent B) paracrine C) autocrine D) endocrine E) All of these choices are correct.
B) paracrine
32. Platelet-derived growth factor (PDGF) is a signaling molecule that functions in which of the following types of cell signaling? A) contact-dependent B) paracrine C) autocrine D) endocrine E) All of these choices are correct.
B) paracrine
48. Growth factors, such as platelet-derived growth factor, function in _____ signaling. A) autocrine B) paracrine C) endocrine D) contact-dependent
B) paracrine
100. Which of the following steps in a signaling cascade initiated by a G protein-coupled receptor would be DIRECTLY affected in cells cultured in the presence of a non-hydrolyzable ATP analog (the analog could bind to other molecules, but could not be converted to ADP and Pi)? (Select all that apply.) A) protein phosphatase activity B) protein kinase activity C) adenylyl cyclase activity D) phosphodiesterase activity
B) protein kinase activity C) adenylyl cyclase activity
101. Which of the following is responsible for the amplification of an intracellular signal? (Select all that apply.) A) protein phosphatase activity B) protein kinase activity C) adenylyl cyclase activity D) phosphodiesterase activity
B) protein kinase activity C) adenylyl cyclase activity
77. Which type of cell-surface receptor undergoes changes in phosphorylation in response to binding of its ligand? A) G protein-coupled receptor B) receptor kinase C) ligand-gated ion channel D) both the G protein-coupled receptor and the receptor kinase
B) receptor kinase
75. Which one of the following is NOT a cell surface-type receptor? A) G protein-coupled receptor B) steroid receptor C) ligand-gated receptor D) receptor kinase
B) steroid receptor
79. How does an "activated" receptor transfer information into the cell? A) by altering the ligand-binding site of the receptor B) through a conformational change of the receptor C) by decreased phosphorylation of the receptor D) by increased translation of the receptor
B) through a conformational change of the receptor
57. Signaling molecules involved in paracrine and autocrine signaling: A) remain attached to the plasma membrane. B) travel by diffusion. C) travel in the circulatory system.
B) travel by diffusion.
93. When a ligand binds to a G protein-coupled receptor, which of the following would you expect to happen FIRST? A) The amount of cAMP in the cytoplasm increases. B) Protein kinase activity increases. C) Adenylyl cyclase activity increases. D) Phosphodiesterase activity increases. E) None of the other answer options is correct.
C) Adenylyl cyclase activity increases.
9. In which of the following is cell signaling prevented? A) The nicotine in cigarette smoke binds to and activates the acetylcholine receptor in plasma membranes of neurons in the brain. B) Proteins on the surface of cells in taste buds called umami receptors bind to glutamates and nucleotides in food, which changes the membrane potential of these cells and tells the brain, "This is savory." C) Allergy medicines, which are called antihistamines, bind to and block histamine receptors to keep fluids in capillaries that would normally be released and cause stuffy noses and watery eyes.
C) Allergy medicines, which are called antihistamines, bind to and block histamine receptors to keep fluids in capillaries that would normally be released and cause stuffy noses and watery eyes.
62. How are steroid hormone receptors and cell-surface receptors similar? A) When bound to their ligand, both types enter the nucleus to activate transcription. B) Both types cause G proteins to exchange GDP for GTP. C) Both types undergo a conformational change when they bind to their ligand. D) When activated, both types carry signals across the plasma membrane.
C) Both types undergo a conformational change when they bind to their ligand.
68. According to Figure 9.6, what is a key difference between cell signaling by a cell-surface receptor and cell signaling by an intracellular receptor? A) Cell-surface receptors bind to specific signaling molecules; intracellular receptors bind any signaling molecule. B) Cell-surface receptors typically bind to signaling molecules that are smaller than those bound by intracellular receptors. C) Cell-surface receptors bind polar signaling molecules; intracellular receptors bind nonpolar signaling molecules. D) Signaling molecules that bind to cell-surface receptors lead to cellular responses restricted to the cytoplasm; signaling molecules that bind to intracellular receptors lead to cellular responses restricted to the nucleus. E) None of the other answer options is correct.
C) Cell-surface receptors bind polar signaling molecules; intracellular receptors bind nonpolar signaling molecules.
49. In the developing nervous system, _____ is the signaling molecule that results in the differentiation of _____. A) Notch; neurons B) Notch; glial cells C) Delta; glial cells D) Delta; neurons
C) Delta; glial cells
81. What does a ligand-gated channel do? A) It binds small, nonpolar signaling molecules. B) It activates a G protein. C) It allows ions to move across the plasma membrane. D) It triggers the activity of a phosphatase.
C) It allows ions to move across the plasma membrane.
2. Which of the following statements about communication among bacteria is CORRECT? (Select all that apply.) A) At low population density, a high concentration of signaling molecules involved in DNA uptake is typically observed. B) Unlike communication among eukaryotes, no receptor molecule is required in communication among bacteria. C) Small peptides can stimulate a DNA-uptake response. D) Cellular communication in bacteria is based on the same principles as communication among eukaryotic cells.
C) Small peptides can stimulate a DNA-uptake response. D) Cellular communication in bacteria is based on the same principles as communication among eukaryotic cells.
37. Of the choices below, what is the MOST likely reason that paracrine signaling does not activate the cell that is producing the signaling molecule? A) The concentration of the signaling molecule is not high enough. B) The neighboring cells are too far away. C) The cell does not have the proper receptor. D) The cell's receptors have a mutation.
C) The cell does not have the proper receptor.
70. You strip off all proteins on the cell surface by using a protease (an enzyme that destroys proteins). Now, when you add a specific signaling molecule, the cell still responds. Why is this? A) The signaling molecule doesn't need a receptor. B) The signaling molecule is polar and can diffuse into the cell. C) The receptor is in the interior of the cell. D) The signaling molecule is nonpolar and binds a cell-surface receptor.
C) The receptor is in the interior of the cell.
25. Many scientists use chemical inhibitors to interfere with normal signaling pathways within eukaryotic cells. If such inhibitors are large, nonpolar molecules, what is the likely method of action of these chemical inhibitors? A) These chemical inhibitors likely enter eukaryotic cells and interfere with components of the signal transduction pathway. B) These chemical inhibitors likely enter the nucleus and prevent the transcription of the pathway of interest's target genes. C) These chemical inhibitors likely bind to receptors and interfere with receptor activation or signal-receptor binding. D) These chemical inhibitors likely interfere with the termination of signaling, so eukaryotic cells can't process new signals.
C) These chemical inhibitors likely bind to receptors and interfere with receptor activation or signal-receptor binding.
82. Which of the following is a FALSE statement about receptors that are localized to the nucleus? A) They are synthesized in the cytosol. B) They carry a nuclear-localization signal. C) They bind polar ligands. D) They move through a nuclear pore.
C) They bind polar ligands.
28. Vascular endothelial growth factor (abbreviated VEGF and pronounced "Veg-F") is a peptide signaling molecule related to platelet-derived growth factor. VEGF is important in the formation of the circulatory system because its signaling pathway causes the formation of blood vessels in developing embryos during normal development. Tumors also produce and secrete VEGF, causing the formation of new blood vessels that supply these tumors. Given what you know about the different kinds of cell signaling and VEGF, which one of the following statements is TRUE? A) VEGF is an endocrine-signaling molecule because it circulates through the bloodstream inside of platelets. B) VEGF is an endocrine-signaling molecule because it is released from platelets into the bloodstream and is carried throughout the body, causing widespread activation of platelet-derived growth factor receptors on cells in a variety of tissues. C) VEGF is a paracrine signaling molecule because it binds to receptors on cells at the site where new blood vessels are needed.
C) VEGF is a paracrine signaling molecule because it binds to receptors on cells at the site where new blood vessels are needed.
60. A drug designed to inhibit the response of cells to the steroid testosterone would almost certainly result in which of the following? A) lower levels of cAMP B) a decrease in receptor kinase activity C) a decrease in the transcription of certain genes D) an increase in cytosolic calcium levels E) a decrease in G protein activity
C) a decrease in the transcription of certain genes
4. A protein on a cell surface that binds to a signaling molecule is an example of which of the following elements of cellular communication? A) a signaling cell B) a signaling molecule C) a receptor protein D) a responding cell E) None of the other answer options is correct.
C) a receptor protein
23. Many diseases are the result of a problem with cell signaling. Which of the following diseases BEST exemplifies this fact? A) cystic fibrosis, which is caused by a mutation in a channel protein, resulting in a buildup of mucus B) congestive heart failure, which is caused by chronic high blood pressure due to excessive sodium intake C) a specific type of cancer, which is caused by a truncated receptor that becomes stuck in the activated for. D) familial hypercholesterolemia (high cholesterol in the blood), which is caused by a decrease in the number of receptors for cholesterol.
C) a specific type of cancer, which is caused by a truncated receptor that becomes stuck in the activated for.
90. Which of the following events are listed in the CORRECT order? A) cAMP activates adenylyl cyclase, which activates protein kinase A B) protein kinase A phosphorylates adenylyl cyclase, which then synthesizes cAMP from ATP C) adenylyl cyclase catalyzes the formation of cAMP, which activates protein kinase A
C) adenylyl cyclase catalyzes the formation of cAMP, which activates protein kinase A
33. Which of the following is a type of cell communication where the signaling molecule is released by the same cell that responds to the signal? A) contact-dependent B) paracrine C) autocrine D) endocrine E) All of these choices are correct.
C) autocrine
39. Which of the following CORRECTLY lists the types of cellular communication from shortest to longest distance traveled by the signaling molecule to reach its responding cell? A) paracrine, autocrine, endocrine B) autocrine, endocrine, paracrine C) autocrine, paracrine, endocrine D) endocrine, paracrine, autocrine
C) autocrine, paracrine, endocrine
65. Despite their differences, steroid hormones: A) have the same effect on different types of cells. B) bind to cell-surface receptors. C) bind intracellular receptors to form complexes that enter the nucleus. D) are hydrophilic small molecules that bind to intracellular receptors. E) facilitate the initiation of translation by ribosomes.
C) bind intracellular receptors to form complexes that enter the nucleus.
40. Which of the following types of cell signaling generally occurs between cells that are distant from each other? A) paracrine B) autocrine C) endocrine D) All of these choices are correct.
C) endocrine
34. Kohler and Lipton first discovered platelet-derived growth factor by observing that fibroblasts: A) could not grow in cell culture without adding PDGF to the growth medium. B) could not grow in cell culture without adding bovine blood serum to the growth medium. C) grew better in cell culture when blood serum was added to the growth medium instead of D) blood plasma. E) could not grow and repair wounding without the action of platelets. F) could not grow in cell culture without the addition of purified red blood cells.
C) grew better in cell culture when blood serum was added to the growth medium instead of
69. Which type of receptor is involved in rapid responses of muscle cells and neurons? A) G protein-coupled receptor B) receptor kinase C) ligand-gated ion channel D) intracellular receptor
C) ligand-gated ion channel
66. Which type of receptor does NOT generally lead to a signaling cascade in the cell that involves the transfer of phosphate groups? (Select all that apply.) A) G protein-coupled receptor B) receptor kinase C) ligand-gated ion channel D) intracellular receptor
C) ligand-gated ion channel D) intracellular receptor
86. A researcher is using a small molecule as an inhibitor to manipulate a signaling pathway. This inhibitor prevents phosphorylation and MOST likely targets a: A) G protein-coupled receptor. B) G protein. C) receptor kinase. D) ligand-gated ion channel. E) phosphatase.
C) receptor kinase.
15. Which of the following is NOT an essential element involved in communication between all cells? A) responding cell B) signaling molecule C) second messenger D) receptor protein
C) second messenger
47. Cell signaling between two nerve cells can be thought of as an example of paracrine signaling because: A) a signaling molecule (neurotransmitter) is released. B) a receptor is activated. C) the cells are in close proximity. D) the responding cell releases more of the signaling molecule (neurotransmitter).
C) the cells are in close proximity.
74. What determines the specificity of a receptor protein? A) the cytoplasmic domain B) the transmembrane domain C) the ligand-binding site D) the extracellular domain
C) the ligand-binding site
20. The ability of a specific tissue or organ to respond to the presence of a hormone is dependent on: A) the location of the tissue or organ with respect to the circulatory path. B) the membrane potential of the cells of the target organ. C) the presence of the appropriate receptors on the cells of the target tissue or organ. D) nothing. All hormones of the body are able to stimulate all cell types because hormones are powerful and nonspecific.
C) the presence of the appropriate receptors on the cells of the target tissue or organ.
21. The first event that happens after a signaling molecule binds to a receptor is: A) the receptor transmits the message in a process called signal transduction. B) there is a cellular response. C) the receptor is activated. D) the signal is quickly terminated to ensure a moderate response.
C) the receptor is activated.
45. The signaling molecule involved in contact-dependent cell signaling is a: A) small soluble peptide. B) neurotransmitter. C) transmembrane protein. D) growth factor.
C) transmembrane protein.
19. Which of the following is a cellular response to signal transduction? A) a change in the proteins found in the cytosol B) the release of more signal molecules C) a change in the activity of an enzyme D) All of these choices are correct.
D) All of these choices are correct.
44. What is a growth factor? A) a small protein that influences cell growth and division B) a signaling molecule involved in paracrine signaling C) a soluble molecule that can alter gene expression in a cell D) All of these choices are correct.
D) All of these choices are correct.
5. To have communication between cells, you must have a: A) receptor. B) signaling molecule. C) responding cell. D) All of these choices are correct.
D) All of these choices are correct.
87. A researcher is studying a G protein-coupled receptor in eukaryotic cells. In one group of cells, he notices that even though a ligand can bind to its G protein-coupled receptor, nothing happens. Why could this happen? A) The G protein-coupled receptor might carry a mutation, so that it fails to undergo a conformational change upon the binding of its ligand. B) The G protein-coupled receptor might carry a mutation that affects the receptor's transmembrane portion. C) These cells might carry mutations in the downstream signaling pathway associated with this G protein-coupled receptor. D) All of these choices are correct.
D) All of these choices are correct.
83. Why don't steroid hormones bind to transmembrane cell-surface receptors? A) Steroid hormones don't require receptors because they bind directly to DNA. B) Steroid hormones are not signaling molecules. C) Steroid hormones are nonpolar and, therefore, cannot bind to receptors. D) Steroid hormones are nonpolar and, therefore, are able to cross the cell's plasma membrane, thus binding to receptors inside the cell.
D) Steroid hormones are nonpolar and, therefore, are able to cross the cell's plasma membrane, thus binding to receptors inside the cell.
98. How would the signal of a G protein-coupled receptor, without ligand, be affected if you made a G protein that converted GDP to GTP on its own without needing to be activated by the G protein-coupled receptor? A) The signal wouldn't be affected; there is no ligand, thus no signal. B) The signal wouldn't be affected; the ligand would be unable to bind due to the conformational change. C) The G protein would be active but unable to signal due to the lack of ligand. D) The G protein would be active and signaling, despite the lack of ligand.
D) The G protein would be active and signaling, despite the lack of ligand.
55. Imagine that a researcher is studying the embryonic development of mice that do not express the signal molecule Delta. What will likely be TRUE of these mice? A) These mice will have more neurons compared with their normal counterparts. B) These mice will have fewer neurons compared with their normal counterparts. C) These mice will have more glia compared with their normal counterparts. D) The mice will have fewer glia compared with their normal counterparts. E) The mice will have fewer neurons and more glia compared with their normal counterparts.
D) The mice will have fewer glia compared with their normal counterparts.
85. A researcher has discovered a new ligand that can pass through the cell membrane and bind to a receptor in the nucleus. Which of the following statements is FALSE regarding this ligand? A) This ligand is likely a steroid. B) This ligand is likely nonpolar. C) This ligand likely has a similar structure to cholesterol. D) This ligand likely binds to a transmembrane receptor. E) This ligand likely plays a role in transcription.
D) This ligand likely binds to a transmembrane receptor.
36. You create a cell that has a mutation in a receptor protein that binds a signaling molecule, which is also produced by the same cell. When you overexpress the signaling molecule produced by this cell, nothing happens. What is defective in this cell? A) endocrine signaling B) contact-dependent signaling C) paracrine signaling D) autocrine signaling
D) autocrine signaling
80. Where would you expect to find the receptor for a nonpolar ligand? A) on the cell surface B) in the nucleus of the cell C) in the cytosol D) either in the nucleus of the cell or in the cytosol
D) either in the nucleus of the cell or in the cytosol
46. Which signaling system involves the LONGEST time interval between release of a signaling molecule and activation of a receptor? A) autocrine B) contact-dependent C) paracrine D) endocrine
D) endocrine
89. A newly discovered signaling molecule that binds to a G protein-coupled receptor is being studied by using cells maintained in cell culture. Preliminary results show that the binding of this new ligand causes the activation of adenylyl cyclase. In the next part of this study, a non-hydrolyzable version of GTP (a form of GTP that cannot be converted to GDP) is added to the cell culture dishes and is taken up by the cells. Which of the following would you expect to observe? A) increased cAMP, decreased protein kinase A activity B) decreased cAMP, decreased protein kinase A activity C) decreased cAMP, increased protein kinase A activity D) increased cAMP, increased protein kinase A activity
D) increased cAMP, increased protein kinase A activity
14. Which is the CORRECT order for these steps in cell signaling? A) signal transduction, receptor activation, response B) response, signal transduction, termination C) receptor activation, response, signal transduction D) receptor activation, signal transduction, response
D) receptor activation, signal transduction, response
64. Ion channels can be involved in cell signaling because: A) they interact with G proteins. B) they lead to receptor phosphorylation. C) their signal is amplified in the cell by a series of phosphorylation events. D) they receive signals from other cells and lead to a cellular response. E) Ion channels are not involved in cell signaling.
D) they receive signals from other cells and lead to a cellular response.
10. Which of the following types of cellular activities can be a response to cell signaling? A) Cell division is triggered. B) Gene expression patterns are changed. C) Enzyme activities are changed. D) Cell signals are released to communicate with other cells. E) All of these choices are correct.
E) All of these choices are correct.
103. Second messengers: A) are small intracellular molecules that participate in signal transduction. B) play a role in activation of intracellular signal transduction. C) are removed in order to terminate a cellular signaling response. D) amplify the effects of the signal. E) All of these choices are correct.
E) All of these choices are correct.
35. Which of the following is TRUE about the Delta protein? A) Delta is a transmembrane protein found in embryonic brain cells. B) Delta is produced by embryonic stem cells as they differentiate into neurons in the brain. C) Delta directly signals to a Notch transmembrane protein in adjacent cells. D) Delta directs adjacent cells to differentiate into glial cells. E) All of these choices are correct.
E) All of these choices are correct.
41. Types of steroids include: A) sex hormones such as estrogen and testosterone. B) glucocorticoids that regulate blood glucose levels. C) insect molting hormones. D) lipid-soluble hormones derived from cholesterol. E) All of these choices are correct.
E) All of these choices are correct.
99. The extent and duration of a cellular response to a signal depend on the: A) binding affinity of the receptor to the signaling molecule. B) concentration of the signaling molecule in the vicinity of the receptor. C) level of expression of the signal transduction proteins. D) level of expression of proteins that terminate the response. E) All of these choices are correct.
E) All of these choices are correct.
56. A researcher is evaluating the role of a growth factor during embryonic development. She notices that this factor functions in both neural development and limb development. How is that possible? A) The effects of the growth factor may be concentration-dependent. B) The effects of the growth factor may be dependent on location. C) The growth factor may result in the transcription of different genes, depending on cell type. D) The growth factor may be signaling through different transduction pathways. E) All of these choices are possible explanations for the observations.
E) All of these choices are possible explanations for the observations.
26. A researcher introduces a signal produced by bacteria to eukaryotic cells that she is culturing in the laboratory. Remarkably, she notices that this signal results in an increase in eukaryotic gene expression. How is this possible? A) This signal is likely similar in structure to ligands utilized by eukaryotic cells. B) This signaling pathway might actually be used by both prokaryotes and eukaryotes. C) This gene expression is likely independent of the presence of the prokaryotic signal. D) This prokaryotic signal likely travels directly into eukaryotic cells and acts as a transcription factor. E) The signal is either similar in structure to a ligand used by eukaryotes, or this signaling pathway is used by both prokaryotes and eukaryotes.
E) The signal is either similar in structure to a ligand used by eukaryotes, or this signaling pathway is used by both prokaryotes and eukaryotes.
