Deck 12: Biosignaling

Question 1

Which item does NOT use a cAMP-dependent signaling pathway?

A) insulin
B) epinephrine
C) ddorants
D) spicy tastes
E) growth factors

Answer 1

A

Question 2

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.

Answer 2

C

Question 3

Cholera and pertussis toxins are:

A) enzyme inhibitors.
B) enzyme modifiers.
C) enzymes.
D) G-protein signal transduction disrupters.
E) All of the answers are correct.

Answer 3

E

Question 4

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 5

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 6

Autophosphorylation of receptor tyrosine kinases depends on:

A) dimerization of the receptor.
B) ATP.
C) ligand binding.
D) transmission of conformational changes through the membrane.
E) All of the answers are correct.

Question 7

Scatchard analysis can provide information on:

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

Question 8

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 9

Which factor 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 10

Which statement 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.

Question 11

Which statement 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 12

Which statement 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 13

_____ 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 these are involved.

Question 14

The specificity of signaling pathways does NOT include:

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 15

_____ do(es) NOT bind to heterotrimeric G proteins.

A) GTP-GDP exchange factors (GEFs)
B) GTPase activating proteins (GAPs)
C) GPCRs
D) cGMP
E) GDP

Question 16

Which item 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 17

Which factor 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 18

Which compound(s) is/are involved in desensitization of the $\beta$ -adrenergic receptor?

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

Question 19

_____ 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 these are involved.

Question 20

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 21

Which factor 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 22

Proto-oncogenes CANNOT be transformed to oncogenes by:

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 23

Oncogenes that encode _____ are NOT known.

A) cytoplasmic G proteins and protein kinases
B) DNA-dependent RNA polymerases
C) growth factors
D) secreted proteins
E) transmembrane protein receptors

Question 24

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 answers are correct.

Question 25

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 26

Which signaling mechanism 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 27

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.

Question 28

Which statement 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 29

Programmed cell death is called:

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

Question 30

The G protein involved in visual signal transduction is:

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

Question 31

In the plant signaling pathways employing receptor-like kinases (RLKs), what 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 32

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 33

Which statement 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 34

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 35

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 36

Most transduction systems for hormones and sensory stimuli that involve trimeric G proteins do NOT have _____ in common.

A) cyclic nucleotides
B) nuclear receptors
C) receptors that interact with a G protein
D) receptors with multiple transmembrane segments
E) self-inactivation

Question 37

Which statement 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 38

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 39

Mutations are NOT part of the progression from normal to cancerous cells in colorectal cancer in:

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 40

Which statement does NOT describe 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 41

Salbutamol is an epinephrine agonist for the $\beta$ -adrenergic receptor. What effects would you expect to see if you treat a hepatocyte with salbutamol?

A) inactivation of adenylylcyclase
B) activation of glycolysis
C) activation of glycogenolysis
D) glucose export from cells
E) both activation of glycogenolysis and glucose export from cells

Question 42

Glycogen synthase kinase (GSK3):

A) is inhibited by phosphorylation of a tyrosine in GSK3.
B) inhibits glycogen synthase.
C) is a tyrosine kinase.
D) is both inhibited by phosphorylation of a tyrosine in GSK3 and is a tyrosine kinase.
E) both inhibits glycogen synthase and is a tyrosine kinase.

Question 43

Cholera toxin leads to the activation of the $\alpha$ subunit of G-proteins through what kind of covalent modification?

A) phosphorylation
B) adenylylation
C) acetylation
D) palmitoylation
E) ADP-ribosylation

Question 44

If a FRET experiment was carried out with blue fluorescent protein attached to the $\alpha$ subunit of a stimulatory G-protein and a green fluorescent protein attached to the $\beta$ subunit, the presence of a strong FRET signal would be associated with:

A) interaction of a G protein-coupled receptor with an antagonist.
B) hydrolysis of GTP in the $\alpha$ subunit.
C) increased concentrations of cAMP.
D) both interaction of a G protein-coupled receptor with an antagonist and hydrolysis of GTP in the $\alpha$ subunit.
E) both hydrolysis of GTP in the $\alpha$ subunit and increased concentrations of cAMP.

Question 45

In the insulin-receptor-dependent activation of the protein ERK (extracellular regulated kinase), what protein is responsible for phosphorylating ERK?

A) the insulin receptor (INSR)
B) insulin receptor substrate-1 (IRS-1)
C) Raf-1 kinase
D) MEK
E) Ras

Question 46

Which statement is TRUE regarding the Na⁺ voltage-gated channel in neurons?

A) Similar to the potassium ion channel, it exists as a tetramer in the membrane.
B) Positive membrane potentials on the extracellular side will close the channel.
C) Aspartate residues are part of the voltage-sensing helices.
D) Ion specificity comes from the voltage-sensing helices.

Question 47

How does the insulin receptor differ from the erythropoietin receptor?

A) Upon binding its signal molecule, the insulin receptor has two-fold symmetry, while the erythropoietin receptor does not.
B) Both the insulin and erythropoietin receptors trigger MAPK cascades.
C) The insulin receptor contains a tyrosine kinase, while the erythropoetin receptor does not.
D) The insulin receptor is phosphorylated in response to signal molecule binding, while the erythropoietin receptor does not.

Question 48

Which statement BEST describes the concept of "amplification" in biosignaling?

A) Higher concentrations of signal molecules lead to stronger cellular responses.
B) In response to the presence of a signal molecule, more signal molecules are synthesized.
C) Small amounts of extracellular signal will trigger multiple intracellular effects via enzyme cascades.
D) All of the statements describe this concept.
E) None of the statements describes this concept.

Question 49

In kidneys, what is the response when the atrial natriuretic factor (ANF) binds to its receptor?

A) increased cAMP concentration in the cytosol
B) activation of protein kinase G (PKG)
C) stimulation of water and sodium excretion
D) both increased cAMP concentration in the cytosol and stimulation of water and sodium excretion
E) both increased cAMP concentration in the cytosol and activation of protein kinase G (PKG)

Question 50

GTP binding to which subunit in a heterotrimeric G-protein is associated with a receptor signal?

A) the $\alpha$ subunit
B) the $\beta$ subunit
C) the $\gamma$ subunit
D) a $\beta$ / $\gamma$ dimer
E) None of the answers is correct.

Question 51

Which feature of signal-transduction comes from high structural and chemical complementarity between a signal molecule and its receptor?

A) specificity
B) cooperativity
C) amplification
D) desensitization
E) integration

Question 52

Which gated ion channel is associated with membrane repolarization in neurons?

A) Na⁺ channel
B) K⁺ channel
C) Ca²⁺ channel
D) acetylcholine receptor ion channel
E) both Na⁺ and Ca²⁺ channels

Question 53

SH2 domains bind sequences containing:

A) phosphoserine
B) phosphothreonine.
C) phosphotyrosine.
D) multiple phosphorylations.
E) either phosphoserine or phosphothreonine.

Question 54

G protein-coupled activation of phospholipase C directly generates which second messenger?

A) diacylglycerol
B) inositol-1,4,5-trisphosphate
C) calcium
D) both diacylglycerol and inositol-1,4,5-trisphosphate
E) both inositol-1,4,5-trisphosphate and calcium

Question 55

What is expected to happen when epinephrine binds to its receptor in a myocyte?

A) Intracellular cAMP levels will rise.
B) Glycogen synthase will become active.
C) Glycogen phosphorylase will be phosphorylated.
D) Intracellular cAMP levels will rise, and glycogen phosphorylase will be phosphorylated.
E) Glycogen synthase will become active, and glycogen phosphorylase will be phosphorylated.

Question 56

Protein kinase C is allosterically regulated by which second messengers?

A) inositol triphosphate (IP₃)
B) diacylglycerol (DAG)
C) calcium (Ca²⁺)
D) both diacylglycerol (DAG) and calcium (Ca²⁺)
E) both inositol triphosphate (IP₃) and diacylglycerol (DAG)

Question 57

Which characteristic is NOT one attributed to a second messenger?

A) intracellular signaling molecules
B) molecules that can easily pass across membrane bilayers
C) molecules that can act as allosteric effectors for signaling proteins
D) molecules that can be rapidly converted between active and inactive forms
E) molecules that are synthesized in response to receptor/signal interactions

Question 58

After membrane depolarization in neurons, export of potassium:

A) makes the value of V_m more negative.
B) decreases the concentration gradient for potassium.
C) is energetically favourable.
D) All of the answers are correct.
E) None of the answers is correct.

Question 59

How do G-proteins become deactivated?

A) GDP dissociates from the $\alpha$ subunit.
B) GTP dissociates from the $\alpha$ subunit.
C) ATP is converted to cAMP in the active site.
D) GTP is hydrolyzed to GDP.
E) GDP both dissociates from the $\alpha$ subunit and is hydrolyzed to GDP.

Question 60

Which protein is phosphorylated in response to an insulin/insulin receptor interaction?

A) IRS-1
B) phosphatidyl inositol-4,5-bisphosphate
C) GDP
D) both IRS-1 and phosphatidyl inositol-4,5-bisphosphate
E) both phosphatidyl inositol-4,5-bisphosphate and GDP

Question 61

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

Question 62

Explain the importance of membrane rafts in cell signaling pathways.

Question 63

Describe the sequence of biochemical events between the release of epinephrine into the bloodstream and the activation of the enzyme glycogen phosphorylase.

Question 64

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

Question 65

Phosphorylation of a threonine in the T-loop of cyclin-dependent kinases (CDK) causes what event to occur?

A) The T loop is rearranged so that cyclin can bind.
B) ADP is forced to dissociate from CDK.
C) The CDK is inactivated.
D) Multiple arginine residues form ionic interactions with the threonine.

Question 66

Which process acts through a G protein-coupled receptor?

A) $\beta$ -adrenergic response
B) light detection by rhodopsin
C) insulin-dependent activation of protein kinase B
D) both $\beta$ -adrenergic response and light detection by rhodopsin
E) both light detection by rhodopsin and insulin-dependent activation of protein kinase B

Question 67

Acetylcholine:

A) is a positively charged molecule.
B) triggers active transport of sodium and calcium into neurons.
C) leads to membrane depolarization through potassium ion import.
D) All of the answers are correct.
E) None of the answer is correct.

Question 68

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 69

Why is estrogen associated with carrier proteins in the blood?

A) Carrier proteins are necessary to import estrogen into cells.
B) Estrogen has only limited solubility in the bloodstream.
C) Estrogen is very unstable in the blood.
D) The carrier proteins bind with estrogen to receptors.

Question 70

Explain how amplification occurs in signal transductions with examples from all three of these systems: the $\beta$ -adrenergic receptor, the insulin receptor, or the vasopressin system via inositol-1,4,5-trisphosphate (IP₃).

Question 71

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 72

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

Question 73

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

Question 74

In the two-component signaling mechanism in E. coli chemotaxis, which amino acid is phosphorylated?

A) serine
B) histidine
C) aspartate
D) threonine
E) both histidine and aspartate

Question 75

Phosphorylation of a tyrosine in the cyclin-dependent kinases (CDK) inactivates the protein by:

A) inhibiting the binding of cyclin.
B) inhibiting the binding of ATP.
C) inhibiting the binding of the "T loop."
D) preventing dissociation of the CDK/cyclin complex.

Question 76

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

Question 77

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 78

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

Question 79

What is meant by multivalent adaptor proteins in signaling pathways?

Question 80

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?