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Chapter 12 Biosignaling
Multiple Choice Questions
1. General Features of Signal Transduction
Which of the following is not involved in the specificity of signal transduction?
A) Interactions between receptor and signal molecules
B) Location of receptor molecules
C) Structure of receptor molecules
D) Structure of signal molecules
E) Transmembrane transport of signal molecules by receptor molecules
2. General Features of Signal Transduction
Which of the following is not a feature of signal transduction?
A) Integration of multiple pathways toward the same downstream response
B) Signal amplification
C) Covalent binding between the ligand and the receptor
D) Desensitization or adaptation of the receptor
E) Variable affinity for different signaling components
3. General Features of Signal Transduction
Scatchard analysis can provide information on:
A) enzyme cascades.
B) enzyme mechanisms.
C) gated ion channels.
D) protein phosphorylation.
E) receptor-ligand interactions.
4. General Features of Signal Transduction
Which of the following statements concerning receptor enzymes is correct?
A) They are not usually membrane-associated proteins.
B) They contain an enzyme activity that acts on a cytosolic substrate.
C) They contain an enzyme activity that acts on the extracellular ligand.
D) They have a ligand-binding site on the cytosolic side of the membrane.
E) They have an active site on the extracellular side of the membrane.
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5. General Features of Signal Transduction
Which of the following is not one of the general types of signaling mechanisms found in multicellular
organisms?
A) Gated ion channels
B) Receptor tyrosine kinases
C) G protein–coupled receptors
D) Receptor cAMP cyclases
E) Adhesion receptors
6. G protein–coupled receptors and second messengers
Which of the following is not true for G protein–coupled receptors (GPCRs)?
A) Agonists mimic the effect of the natural ligand.
B) Antagonists block the normal effect of the natural ligand.
C) GPCRs interact with heterodimeric G proteins.
D) GPCRs are have seven transmembrane helices.
E) There exist >100 orphan GPCRs in the human genome with no known ligand.
7. G protein–coupled receptors and second messengers
Cholera and pertussis toxins are:
A) enzyme inhibitors.
B) enzyme modifiers.
C) enzymes.
D) G protein signal transduction disrupters.
E) All of the above
8. G protein–coupled receptors and second messengers
Protein kinase A (PKA) is:
A) activated by covalent binding of cyclic AMP.
B) affected by cyclic AMP only under unusual circumstances.
C) allosterically activated by cyclic AMP.
D) competitively inhibited by cyclic AMP.
E) noncompetitively inhibited by cyclic AMP.
9. G protein–coupled receptors and second messengers
Which of the following is not involved in signal transduction by the
-adrenergic receptor pathway?
A) ATP
B) Cyclic AMP
C) Cyclic GMP
D) GTP
E) All of the above are involved.
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10. G protein–coupled receptors and second messengers
Which of the following is not involved in signal transduction by the
-adrenergic receptor pathway?
A) Cyclic AMP synthesis
B) GTP hydrolysis
C) GTP-binding protein
D) Protein kinase
E) All of the above are involved.
11. G protein–coupled receptors and second messengers
Which of the following does not bind to heterotrimeric G proteins?
A) GTP-GDP exchange factors (GEFs)
B) GTPase activating proteins (GAPs)
C) GPCRs
D) cGMP
E) GDP
12. G protein–coupled receptors and second messengers
Which of the following are involved in desensitization of the
-adrenergic receptor?
A)
-adrenergic receptor kinase
B) Arrestin
C) GTPase activating proteins (GAPs)
D) A and B above
E) A, B, and C above
13. G protein–coupled receptors and second messengers
Which of the following does not use a cAMP-dependent signaling pathway?
A) Insulin
B) Epinephrine
C) Odorants
D) Spicy tastes
E) Growth factors
14. G protein–coupled receptors and second messengers
Hormone-activated phospholipase C can convert phosphatidylinositol 4,5-bisphosphate to:
A) diacylglycerol + inositol triphosphate.
B) diacylglycerol + inositol+ phosphate.
C) glycerol + inositol + phosphate.
D) glycerol + phosphoserine.
E) phosphatidyl glycerol + inositol + phosphate.
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15. G protein–coupled receptors and second messengers
Calmodulin is a(n):
A) allosteric activator of calcium-dependent enzymes.
B) allosteric inhibitor of calcium-dependent enzymes.
C) calcium-dependent enzyme.
D) cell surface calcium receptor.
E) regulatory subunit of calcium-dependent enzymes.
16. Receptor tyrosine kinases
Autophosphorylation of receptor tyrosine kinases depends on which of the following?
A) Dimerization of the receptor
B) ATP
C) Ligand binding
D) Transmission of conformational changes through the membrane
E) All of the above
17. Receptor tyrosine kinases
Which of the following statements concerning signal transduction by the insulin receptor is not
correct?
A) Activation of the receptor protein kinase activity results in the activation of additional protein
kinases.
B) Binding of insulin to the receptor activates a protein kinase.
C) Binding of insulin to the receptor results in a change in its quaternary structure.
D) The receptor protein kinase activity is specific for tyrosine residues on the substrate proteins.
E) The substrates of the receptor protein kinase activity are mainly proteins that regulate
transcription.
18. Receptor tyrosine kinases
What is the correct order for the following members of the MAP Kinase cascade?
1) MEK
2) ERK
3) Raf
4) RTK
A) 4, 2, 3, 1
B) 2, 1, 3, 4
C) 4, 3, 1, 2
D) 4, 1, 2, 3
E) 4, 3, 2, 1
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19. Receptor guanylyl cylases, cGMP, and protein kinase G
Guanyl cyclase receptor enzymes:
A) are all membrane-spanning proteins.
B) are examples of ligand-gated ion channels.
C) catalyze synthesis of a phosphate ester.
D) catalyze synthesis of a phosphoric acid anhydride
E) require hydrolysis of ATP in addition to GTP.
20. Multivalent adaptor proteins and membrane rafts in signaling
The specificity of signaling pathways includes all of the following except:
A) flippase-catalyzed movement of phospholipids from the inner to the outer leaflet.
B) migration of signal proteins into membrane rafts.
C) phosphorylation of target proteins at Ser, Thr, or Tyr residues.
D) the ability to be switched off instantly by hydrolysis of a single phosphate-ester bond.
E) the assembly of large multiprotein complexes.
21. Gated ion channels
The force that drives an ion through a membrane channel depends on the:
A) charge on the membrane.
B) difference in electrical potential across the membrane.
C) size of the channel.
D) size of the ion.
E) size of the membrane.
22. Gated ion channels
The ion channel that opens in response to acetylcholine is an example of a ____________ signal
transduction system.
A) G-protein
B) ligand-gated
C) receptor-enzyme
D) serpentine receptor
E) voltage-gated
23. Gated ion channels
The effects of acetylcholine on the postsynaptic ion channel are mainly due to:
A) cyclic nucleotide synthesis.
B) protein cleavage (proteolysis).
C) protein conformational changes.
D) protein phosphorylation.
E) protein synthesis.
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24. Gated ion channels
Which of the following is true of gated ion channels?
A) Each channel can allow 10 million ions per second through the membrane.
B) The gating mechanism involves piston-like movement of the transmembrane helices.
C) Each channel lets both positive and negative ions flow through the pore.
D) Closing of the gate requires phosphorylation of the channel protein.
E) Gated channels only respond to intracellular ligands.
25. Integrins: Bidirectional cell adhesion receptors
Which of the following is not true of integrins?
A) Integrins are rich in cysteines.
B) Integrins are internalized following binding to external ligands.
C) Integrins have more than one subunit.
D) Integrins interact with Ca2+ ions.
E) Integrins bind to extracellular matrix components such as collagen and heparan sulfate.
26. Regulation of transcription by steroid hormones
Steroid hormones are carried on specific carrier proteins because the hormones:
A) are too unstable to survive in the blood on their own.
B) cannot dissolve readily in the blood because they are too hydrophobic.
C) cannot find their target cells without them.
D) need them in order to pass through the plasma membrane.
E) require subsequent binding to specific receptor proteins in the nucleus.
27. Regulation of transcription by steroid hormones
Steriod hormone response elements (HREs) are __________ , which, when bound to
_____________, alter gene expession at the level of ________________.
A) intron sequences; activated hormone receptor; translation
B) nuclear proteins; hormone; transcription
C) plasma membrane proteins; hormone; transcription
D) sequences in DNA; receptor-hormone complex; replication
E) sequences in DNA; receptor-hormone complex; transcription
28. Signaling in microorganisms and plants
Which one of the following signaling mechanisms is used most predominantly in plants?
A) Cyclic-nucleotide dependent protein kinases
B) DNA-binding nuclear steroid receptors
C) G protein–coupled receptors
D) Protein serine/threonine kinases
E) Protein tyrosine kinases
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29. Signaling in microorganisms and plants
In the plant signaling pathways employing receptor-like kinases (RLKs), which one of the following
does not occur?
A) Activation of a MAPK cascade
B) Autophosphorylation of receptor
C) Dimerization of receptor
D) Ligand binding to receptor
E) Phosphorylation of key proteins on Tyr residues
30. Sensory transduction in vision, olfaction, and gustation
Most transduction systems for hormones and sensory stimuli that involve trimeric G proteins have in
common all of the following except:
A) cyclic nucleotides.
B) nuclear receptors.
C) receptors that interact with a G protein.
D) receptors with multiple transmembrane segments.
E) self-inactivation.
31. Sensory transduction in vision, olfaction, and gustation
The G protein involved in visual signal transduction is:
A) a leukotriene.
B) transducin.
C) arrestin.
D) rhodopsin.
E) a GTP receptor.
32. Sensory transduction in vision, olfaction, and gustation
Which of the following is not a step in the response to photon absorption by rhodopsin?
A) Rhodopsin catalyzes GDP/GTP exchange on transducin.
B) Rhodopsin is phosphorylated by rhodopsin kinase.
C) Arrestin binds to the phosphorylated end of rhodopsin.
D) Light absorption converts all-trans-retinal to 11-cis-retinal.
E) All-trans-retinal is replaced with 11-cis-retinal.
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33. Sensory transduction in vision, olfaction, and gustation
Which of the following is not a shared feature of signaling by mammalian vision and gustatory
receptor pathways?
A) Changes in cAMP levels
B) GDP/GTP exchange
C) Heterotrimeric G proteins
D) Open/closing of ion channels
E) Transmembrane receptors
34. Regulation of the cell cycle by protein kinases
Which of the following statements concerning cyclin-dependent protein kinases is not correct?
A) Each type of cell contains one specific form (isozyme).
B) Their activity fluctuates during the cell cycle.
C) Their activity is regulated by changes in gene expression, protein phosphorylation, and proteolysis.
D) Their activity is regulated by cyclins.
E) They can alter the activity of proteins involved in the progression of cells through the cell cycle.
35. Regulation of the cell cycle by protein kinases
Which of the following statements concerning cyclins is not correct?
A) They are activated and degraded during the cell cycle.
B) They are regulatory subunits for enzymes that catalyze the phosphorylation of proteins.
C) They can become linked to ubiquitin.
D) They catalyze the phosphorylation of proteins.
E) They contain specific amino acid sequences that target them for proteolysis.
36. Regulation of the cell cycle by protein kinases
Ubiquitin is a:
A) component of the electron transport system.
B) protease.
C) protein kinase.
D) protein phosphorylase.
E) protein that tags another protein for proteolysis.
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37. Regulation of the cell cycle by protein kinases
Cyclin-dependent protein kinases can regulate the progression of cells through the cell cycle by
phosphorylation of proteins such as:
A) insulin.
B) myoglobin.
C) myosin.
D) retinal rod and cone proteins.
E) All of the above
38. Oncogenes, tumor suppressor genes and programmed cell death
Proto-oncogenes can be transformed to oncogenes by all of the following mechanisms except:
A) chemically induced mutagenesis.
B) chromosomal rearrangements.
C) during a viral infection cycle.
D) elimination of their start signals for translation.
E) radiation-induced mutation.
39. Oncogenes, tumor suppressor genes and programmed cell death
Oncogenes are known that encode all of the following except:
A) cytoplasmic G proteins and protein kinases.
B) DNA-dependent RNA polymerases.
C) growth factors.
D) secreted proteins.
E) transmembrane protein receptors.
40. Oncogenes, tumor suppressor genes and programmed cell death
Programmed cell death is called:
A) metastasis.
B) apoptosis.
C) mitotic termination.
D) oncogenic transformation.
E) ubiquitination.
41. Oncogenes, tumor suppressor genes and programmed cell death
Mutations in which of the following are not part of the progression from normal to cancerous cells in
colorectal cancer?
A) Abl involved in cellular signaling
B) KRAS and BRAF kinases involved in cellular signaling
C) PI3K and PTEN involved in cellular signaling
D) MMR involved in DNA repair
E) CDC4 involved in ubiquitination
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Short Answer Questions
42. Molecular mechanisms of signal transduction
Pages: 433–434 Difficulty: 2
Describe three factors that contribute to the high degree of sensitivity of signal transduction systems.
43. Molecular mechanisms of signal transduction
Pages: 433–444 Difficulty: 2
Explain how amplification of a hormonal signal takes place; illustrate with a specific example.
44. Molecular mechanisms of signal transduction
Page: 435 Difficulty: 3
What is a Scatchard plot, and how can it be used to determine the number of receptor molecules on a
cell and their affinity for a ligand?
45. G Protein-coupled receptors and second messengers
Pages: 442–443 Difficulty: 3
The toxins produced by Bordetella pertussis (which causes whooping cough) and by Vibrio cholerae
(which causes cholera) have similar modes of action in toxin-sensitive mammalian cells. Describe
the molecular basis for their toxic effects.
Chapter 12 Biosignaling
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46. G Protein-coupled receptors and second messengers
Page: 444 Difficulty: 3
Describe the sequence of biochemical events between the release of epinephrine into the bloodstream
and the activation of the enzyme glycogen phosphorylase.
47. G Protein-coupled receptors and second messengers
Pages: 444–452 Difficulty: 3
Signals carried by hormones must eventually be terminated; the response continues for a limited time.
Discuss three different mechanisms for signal termination, using specific systems as examples.
48. G Protein-coupled receptors and second messengers
Pages: 444–457 Difficulty: 3
Explain how amplification occurs in signal transductions with examples from all three of these
systems: the
-adrenergic receptor, the insulin receptor, or the vasopressin system via inositol-1,4,5-
trisphosphate (IP3).
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49. G Protein-coupled receptors and second messengers
Pages: 439–450 Difficulty: 3
GTP-binding proteins play critical roles in many signal transductions. Describe two cases in which
such proteins act, and compare the role of the G proteins in each case.
50. G Protein-coupled receptors and second messengers
Pages: 439–444, 453–455 Difficulty: 3
Compare and contrast the modes of action of epinephrine, acting through the
-adrenergic receptor,
and of insulin, acting through the insulin receptor.
51. G Protein-coupled receptors and second messengers
Pages: 451–452 Difficulty: 3
Explain how an increase in cytosolic Ca2+ concentration from 10-8 M to 10-6 M activates a Ca2+ and
calmodulin-dependent enzyme.
the activity of a number of enzymes.
52. Receptor tyrosine kinases
Page: 457 Difficulty: 3
Explain how the cytokine erythropoetin activates transcription of specific genes essential in blood
maturation.
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53. Receptor guanylyl cylases, cGMP, and protein kinase G
Pages: 459–460 Difficulty: 2 Ans: C
Briefly compare the two types of guanylyl cyclases that participate in signal transduction.
54. Multivalent adaptor proteins and membrane rafts
Pages: 460–463 Difficulty: 2
What is meant by multivalent adaptor proteins in signaling pathways?
55. Multivalent adaptor proteins and membrane rafts
Page: 463 Difficulty: 2
Explain the importance of membrane rafts in cell signaling pathways.
56. Gated ion channels
Pages: 465–468 Difficulty: 2
Compare and contrast ligand-gated and voltage-gated ion channels; give an example of each.
57. Gated ion channels
Page: 468 Difficulty: 3
Briefly describe the key features of the voltage-gated Na+-ion channel found in neurons.
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58. Gated ion channels
Page: 469 Difficulty: 3
Briefly describe the key features of the acetylcholine receptor channel.
59. Integrins: Bidirectional cell adhesion receptors
Pages: 470–471 Difficulty: 2 Ans: B
What are the extracellular and intracellular molecules that interact with integrins?
60. Regulation of transcription by steroid hormones
Pages: 471–472 Difficulty: 1
What is the mechanism of action of the drug tamoxifen in the treatment of breast cancer?
61. Regulation of transcription by steroid hormones
Pages: 471–472 Difficulty: 2
Describe two examples of steroid hormone action that occur too rapidly to be the consequence of
altered levels of protein synthesis.
62. Signaling in microorganisms and plants
Pages: 473–474 Difficulty: 2
What is meant by the two-component system of bacterial cell signaling?
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63. Signaling in microorganisms and plants
Page: 474–475 Difficulty: 2
Briefly describe the ethylene detection system of plants.
64. Sensory transduction in vision, olfaction, and gustation
Page: 477 Difficulty: 2
How do ligand-gated ion channels play a role in sensory transduction in the eye?
65. Sensory transduction in vision, olfaction, and gustation
Pages: 481–482 Difficulty: 2
Describe the role of G proteins in olfactory sensory transduction
66. Sensory transduction in vision, olfaction, and gustation
Page: 483 Difficulty: 3
Match the signal input with the result:
Input Result
a) Light 1) Sensory cell depolarizes
b) Odorant 2) Sensory cell hyperpolarizes
c) Sweet molecule 3) No effect on sensory cell membrane potential
d) Epinephrine
67. Regulation of cell cycle by protein kinases
Pages: 485–488 Difficulty: 2
What are cyclins? What is their role in the regulation of the cell cycle?
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68. Oncogenes, tumor suppressor genes and programmed cell death
Page: 489 Difficulty: 2
Describe the relationship between a proto-oncogene and an oncogene, and explain how one arises
from the other.
69. Oncogenes, tumor suppressor genes and programmed cell death
Page: 489 Difficulty: 2
Explain how a mutation in the EGF receptor can lead to unregulated cell division.
70. Oncogenes, tumor suppressor genes and programmed cell death
Pages: 489–492 Difficulty: 3
Explain why mutations in oncogenes are generally dominant while those in tumor suppressor genes
are recessive.
71. Oncogenes, tumor suppressor genes and programmed cell death
Pages: 490–491 Difficulty: 3
Explain two different approaches to targeting the activity of aberrant protein kinases for treating
cancer. Give examples of each.
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71. Oncogenes, tumor suppressor genes and programmed cell death
Pages: 435–442, 472–473 Difficulty: 3
Explain how mutations in the following proteins might result in either loss of responsiveness to a
given hormone or production of a continuous signal even in the absence of the hormone: (a) a
mutation in the regulatory (R) subunit of cAMP-dependent protein kinase, making R incapable of
binding to the catalytic (C) subunit; (b) a mutation in a growth factor receptor with protein kinase
activity; (c) a defect in a G protein that renders the GTPase activity inactive.
