Deck 12: Biosignaling

Question 1

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.

Answer 1

They contain an enzyme activity that acts on a cytosolic substrate.

Question 2

Which of the following are involved in desensitization of the $\beta$ -adrenergic receptor?

A)( $\beta$ -adrenergic receptor kinase)
B)Arrestin
C)GTPase activating proteins (GAPs)
D)A and B above
E)A,B,and C above

Answer 2

A and B above

Question 3

Scatchard analysis can provide information on:

A)enzyme cascades.
B)enzyme mechanisms.
C)gated ion channels.
D)protein phosphorylation.
E)receptor-ligand interactions.

Answer 3

receptor-ligand interactions.

Question 4

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

Question 5

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.

Question 6

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.

Question 7

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.

Question 8

Cholera and pertussis toxins are:

A)enzyme inhibitors.
B)enzyme modifiers.
C)enzymes.
D)G protein signal transduction disrupters.
E)All of the above

Question 9

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.

Question 10

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

Question 11

Which of the following does not use a cAMP-dependent signaling pathway?

A)Insulin
B)Epinephrine
C)Odorants
D)Spicy tastes
E)Growth factors

Question 12

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

Question 13

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.

Question 14

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

Question 15

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.

Question 16

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

Question 17

Which of the following is not involved in signal transduction by the $\beta$ -adrenergic receptor pathway?

A)ATP
B)Cyclic AMP
C)Cyclic GMP
D)GTP
E)All of the above are involved.

Question 18

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

Question 19

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.

Question 20

Which of the following is not involved in signal transduction by the $\beta$ -adrenergic receptor pathway?

A)Cyclic AMP synthesis
B)GTP hydrolysis
C)GTP-binding protein
D)Protein kinase
E)All of the above are involved.

Question 21

The G protein involved in visual signal transduction is:

A)a leukotriene.
B)transducin.
C)arrestin.
D)rhodopsin.
E)a GTP receptor.

Question 22

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.

Question 23

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.

Question 24

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.

Question 25

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

Question 26

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.

Question 27

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.

Question 28

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

Question 29

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.

Question 30

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.

Question 31

Programmed cell death is called:

A)metastasis.
B)apoptosis.
C)mitotic termination.
D)oncogenic transformation.
E)ubiquitination.

Question 32

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.

Question 33

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

Question 34

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

Question 35

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.

Question 36

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.

Question 37

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

Question 38

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)E) protein synthesis.

Question 39

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

Question 40

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.

Question 41

What is meant by multivalent adaptor proteins in signaling pathways?

Question 42

Describe three factors that contribute to the high degree of sensitivity of signal transduction systems.

Question 43

Describe two examples of steroid hormone action that occur too rapidly to be the consequence of altered levels of

Question 44

Compare and contrast the modes of action of epinephrine,acting through the $\beta$ -adrenergic receptor,and of insulin,acting through the insulin receptor.

Question 45

Explain the importance of membrane rafts in cell signaling pathways.

Question 46

Explain how amplification of a hormonal signal takes place;illustrate with a specific example.

Question 47

What are the extracellular and intracellular molecules that interact with integrins?

Question 48

What is meant by the two-component system of bacterial cell signaling?

Question 49

Explain how an increase in cytosolic Ca²⁺ concentration from 10^-8 M to 10^-6 M activates a Ca²⁺ and calmodulin-dependent enzyme.

Question 50

Briefly compare the two types of guanylyl cyclases that participate in signal transduction.

Question 51

What is the mechanism of action of the drug tamoxifen in the treatment of breast cancer?

Question 52

Briefly describe the key features of the acetylcholine receptor channel.

Question 53

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?

Question 54

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.

Question 55

Explain how the cytokine erythropoetin activates transcription of specific genes essential in blood maturation.

Question 56

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

Question 57

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.

Question 58

Compare and contrast ligand-gated and voltage-gated ion channels;give an example of each.

Question 59

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.

Question 60

Briefly describe the key features of the voltage-gated Na⁺-ion channel found in neurons.

Question 61

Explain two different approaches to targeting the activity of aberrant protein kinases for treating cancer.Give examples of each.

Question 62

Briefly describe the ethylene detection system of plants.

Question 63

Describe the role of G proteins in olfactory sensory transduction

Question 64

Explain how a mutation in the EGF receptor can lead to unregulated cell division.

Question 65

Describe the relationship between a proto-oncogene and an oncogene,and explain how one arises from the other.

Question 66

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.

Question 67

Explain why mutations in oncogenes are generally dominant while those in tumor suppressor genes are recessive.

Question 68

What are cyclins? What is their role in the regulation of the cell cycle?

Question 69

How do ligand-gated ion channels play a role in sensory transduction in the eye?

Question 70

Match the signal input with the result: