Deck 17: Cell Signaling

Question 1

Signaling by the steroid hormone estrogen is an example of _______ signaling.

A) autocrine
B) endocrine
C) paracrine
D) direct cell-to-cell

Answer 1

B

Question 2

Signaling by neurotransmitters is an example of _______ signaling.

A) autocrine
B) endocrine
C) paracrine
D) direct cell-to-cell

Answer 2

C

Question 3

Stimulation of T lymphocytes, leading to their synthesis of a growth factor resulting in T lymphocyte proliferation, is an example of _______ signaling.

A) autocrine
B) endocrine
C) paracrine
D) direct cell-to-cell

Answer 3

A

Question 4

Signaling by cadherins is an example of _______ signaling.

A) autocrine
B) endocrine
C) paracrine
D) direct cell-to-cell

Question 5

Which signal molecule diffuses through the plasma membrane to ultimately bind nuclear receptors and influence transcription?

A) Estrogen
B) Nitric oxide
C) Cadherins
D) Nerve growth factor

Question 6

Steroid hormones usually act via receptors that

A) are coupled to G proteins that activate adenylyl cyclase.
B) activate tyrosine kinases.
C) bind to DNA.
D) activate phospholipase C.

Question 7

Statins, a class of drugs that are often administered to patients with high cholesterol, inhibit the biosynthesis of cholesterol. Statin drugs would not be expected to affect the biosynthetic pathway of which of the following signal molecules?

A) Thyroid hormone
B) Vitamin D₃
C) Retinoic acid
D) Estrogen

Question 8

A glucocorticoid binding to its receptor stimulates

A) phosphorylation of a transcription factor protein that activates a gene.
B) formation of a receptor dimer that triggers an intracellular signal pathway.
C) formation of a receptor dimer that binds to and activates a gene.
D) binding of the receptor monomer to a gene.

Question 9

Nitric oxide is a signal molecule that can

A) bind to surface receptors and activate second messengers.
B) bind to surface receptors and open ion channels.
C) diffuse across cell membranes and bind to receptors that regulate transcription.
D) diffuse across cell membranes and directly alter the activity of intracellular enzymes.

Question 10

Nitric oxide is considered a paracrine signal molecule because it

A) is slow to diffuse.
B) is produced in very small quantities.
C) is unstable, with a short half-life.
D) binds to cell surface receptors that are very plentiful.

Question 11

The medical usage of nitroglycerine in heart disease is based on its

A) inhibition of adenylate cyclase and blood vessel contraction.
B) conversion to NO and blood vessel dilation.
C) activation of NO-synthase and muscle cell contraction.
D) promotion of cyclooxygenase and prostaglandin synthesis.

Question 12

Neurotransmitters act by binding to receptors that are

A) ligand-gated ion channels.
B) located in the cytoplasm.
C) tyrosine-kinase receptors.
D) not coupled to G proteins.

Question 13

Enkephalins and endorphins bind to the same receptors in the brain as

A) nerve growth factor.
B) aspirin.
C) morphine.
D) acetylcholine.

Question 14

In plants, cytokinins stimulate

A) cell division.
B) cell elongation.
C) cell enlargement.
D) fruit ripening.

Question 15

In plant cells, which signaling molecule induces cell elongation?

A) Acetylcholine.
B) $\gamma$ -aminobutyric acid (GABA).
C) Auxin.
D) Retinoic acid.

Question 16

Which molecule stimulates fibroblasts to proliferate and thus heal a wound?

A) EGF
B) NGF
C) NO
D) PDGF

Question 17

Differentiation of blood cells and control of lymphocytes during the immune response is regulated by which type of signaling molecule?

A) Enkephalins
B) Fibroblast growth factor
C) Platelet derived growth factor
D) Cytokines

Question 18

The G protein that activates adenylyl cyclase is a

A) monomeric G protein in the Ras family that binds GTP.
B) dimeric G protein that separates into $\alpha$ and $\beta$ subunits.
C) heterotrimeric G protein that separates into $\alpha$ and $\beta$$\gamma$ subunits.
D) heterotrimeric G protein that separates into $\alpha$ (\beta\)0 and $\gamma$ subunits.

Question 19

In an active state of a G protein, the

A) $\alpha$ subunit binds to a target protein, and the $\beta$$\gamma$ subunit remains bound to the receptor.
B) $\alpha$ and $\beta$$\gamma$ subunits both can bind to target proteins.
C) $\alpha$$\beta$ and $\gamma$ subunits both can bind to target proteins.
D) $\gamma$ subunit can bind to a target protein, and the $\alpha$$\beta$ subunit remains bound to the receptor.

Question 20

The GTP on the G protein that is linked to adenylyl cyclase is split to GDP and P_i

A) in the inactive state.
B) in the process of subunit separation.
C) upon activation by the receptor.
D) by the active $\alpha$ subunit.

Question 21

Cholera toxin inhibits the ability of the $\alpha$ subunit of G_s to split GTP. If you treated cells with cholera toxin, the resulting effect would be _______ of adenylyl cyclase.

A) stimulation
B) inhibition
C) molecular degradation
D) increased synthesis

Question 22

A mutation that causes a G-protein to lose its ability to hydrolyze bound GTP would be expected to have constitutively

A) inactive $\beta$$\gamma$ subunits.
B) bound $\alpha$$\beta$$\gamma$ subunits.
C) active $\alpha$ subunits.
D) inactive $\alpha$ subunits.

Question 23

The alpha subunit of the G protein that is associated with the epinephrine receptor, G_s,

A) opens Ca²⁺ channels.
B) closes Na⁺ channels.
C) activates adenylate cyclase.
D) inhibits adenylate cyclase.

Question 24

A major function of cAMP in animal cells is to activate

A) adenylyl cyclase.
B) protein kinase A.
C) protein kinase C.
D) tyrosine kinases.

Question 25

Protein kinase A is activated by

A) phosphorylation of its catalytic subunit.
B) phosphorylation of its regulatory subunits.
C) binding of cAMP to its catalytic subunits.
D) binding of cAMP to its regulatory subunits.

Question 26

Binding of cAMP to the _______ subunits of protein kinase A (PKA) leads to _______ of that protein kinase.

A) catalytic; activation
B) catalytic; inactivation
C) regulatory; inactivation
D) regulatory; activation

Question 27

Protein kinase A regulates glycogen metabolism by phosphorylating glycogen synthase and

A) phosphorylase kinase.
B) glycogen phosphatase.
C) glycogen phosphorylase.
D) glucokinase.

Question 28

Protein kinase A regulates glycogen metabolism by _______ glycogen synthase and _______ glycogen phosphorylase.

A) activating; activating
B) inactivating; inactivating
C) activating; inactivating
D) inactivating; activating

Question 29

The action effected by protein kinase A is terminated by

A) inactivation of the initial receptor.
B) inactivation of the stimulatory G protein.
C) degradation of cAMP.
D) dephosphorylation of phosphoproteins by protein phosphatase 1.

Question 30

During the odorant response in the cilia of olfactory neurons, the second messenger _______, leads to the opening of ion channels in the plasma membrane of olfactory neurons and the production of a nerve impulse.

A) Ca²⁺
B) cAMP
C) cGMP
D) IP₃

Question 31

Protein X is activated by protein kinase A. A mutation in protein X that replaces the protein's only serine residue with an arginine residue would be expected to

A) increase activation of protein X.
B) eliminate activation of protein X.
C) have no effect on activation of protein X.
D) prevent inactivation of protein X.

Question 32

CREB is activated by

A) cAMP binding in the nucleus.
B) phosphorylation by protein kinase A in the nucleus.
C) cAMP binding in the cytoplasm.
D) phosphorylation by protein kinase A in the cytoplasm.

Question 33

Which statement correctly describes how protein kinase A can activate genes?

A) Nuclear protein kinase A is activated by cAMP to phosphorylate general transcription factors.
B) Cytosolic protein kinase A is activated by cAMP to release the catalytic subunits, which move into the nucleus and phosphorylate CREB.
C) Cytosolic protein kinase A is activated by cAMP to release the catalytic subunits, which move into the nucleus and phosphorylate general transcription factors.
D) Nuclear protein kinase A is activated by cAMP to phosphorylate CREB.

Question 34

Activated CREB protein

A) phosphorylates protein phosphatase 1, leading to its activation.
B) binds to specific DNA sequences and influences transcription of genes involved in growth and development.
C) binds to ribosomal subunits and influences translation of proteins important in growth and development.
D) phosphorylates protein kinase A in the cytoplasm.

Question 35

The first step in growth factor pathway activation is

A) receptor dimerization.
B) receptor phosphorylation.
C) Ras activation.
D) the binding of SH2-containing proteins.

Question 36

MAP kinase is an abbreviation for _______ protein kinase.

A) microtubule-associated
B) mitogen-activated
C) mitosis-activating
D) mitosis-associated

Question 37

A researcher generated a mutant SH2-containing protein such that it binds tyrosine and phosphotyrosine with equal affinity. As a result, MEK activity would be expected to

A) increase with ligand binding-induced dimerization.
B) remain the same with receptor dimerization and autophosphorylation.
C) decrease due to changes in Raf activation.
D) decrease due to allosteric inhibition of SH2-domain binding.

Question 38

Binding of integrins to the extracellular matrix leads to integrin clustering and activation of the nonreceptor tyrosine kinase

A) CREB.
B) FAK.
C) PKA.
D) Ca²⁺/calmodulin-dependent kinase.

Question 39

Mutated oncogenic Ras proteins usually

A) cleave GTP more rapidly than normal.
B) fail to bind Raf.
C) cleave GTP less rapidly than normal.
D) bind GAP more tightly than normal.

Question 40

Ras is a membrane-bound _______ when activated.

A) small monomeric G protein that binds GTP
B) dimeric G protein that separates into $\alpha$ and $\beta$ subunits
C) heterotrimeric G protein that separates into $\alpha$ and $\beta$$\gamma$ subunits
D) heterotrimeric G protein that separates into $\alpha$$\beta$ and $\gamma$ subunits

Question 41

MAP kinase signal cascades are often organized into functional groups or cassettes by

A) scaffold proteins.
B) binding of SH2 domains to each other.
C) lipid rafts.
D) binding MAP kinase-responsive genes.

Question 42

The RAS guanine nucleotide-binding protein is activated by

A) cAMP binding.
B) serine phosphorylation by protein kinase A.
C) GDP binding.
D) GTP binding.

Question 43

MEK is a protein kinase that phosphorylates _______ residues.

A) threonine and tyrosine
B) tyrosine
C) histidine
D) arginine and lysine

Question 44

Hydrolysis of PIP₂ by phospholipase C is stimulated by

A) G protein-linked receptors.
B) protein-tyrosine kinase receptors.
C) serine-threonine kinase receptors.
D) both G protein-linked receptors and protein-tyrosine kinase receptors.

Question 45

The second messenger, phosphatidylinositol 3,4,5-trisphosphate (PIP₃) is generated by the action of the enzyme _______ on phosphatidylinositol 4,5-bisphosphate (PIP₂).

A) protein kinase A
B) protein kinase C
C) phosphatidylinositide (PI) 3-kinase
D) mTOR kinase

Question 46

The mTOR pathway is a central regulator of cell growth that couples the control of

A) protein synthesis to the availability of growth factors, nutrients,
And energy.
B) DNA replication during mitosis and during meiosis.
C) transcription factors that regulate gene expression in the liver.
D) transcription factors that regulate gene expression in early embryonic development.

Question 47

The TGF- $\beta$ Smad pathway is similar to JAK/STAT signaling in that a protein kinase associated with a receptor directly phosphorylates and activates a transcription factor. However, the receptors for transforming growth factor beta (TGF- $\beta$ ) and related polypeptides are protein kinases that phosphorylate _______, rather than _______, residues on their substrate proteins.

A) serine or threonine; tyrosine
B) tyrosine; serine or threonine
C) proline or aspartate; tyrosine
D) tryptophan; tyrosine

Question 48

NF- $\kappa$ B can activate genes during the immune response by a protein kinase that

A) phosphorylates the transcription factor NF- $\kappa$ B to activate it.
B) phosphorylates the inhibitory factor I $\kappa$ B, causing it to be degraded and to release NF- $\kappa$ B.
C) phosphorylates a MAP kinase to initiate its cascade.
D) activates a phosphorylase that removes an inhibiting phosphate from the NF- $\kappa$ B.

Question 49

Which of the following would lead to a termination of Wnt signaling?

A) Phosphorylation of Disheveled
B) Inactivation of the destruction complex
C) Phosphorylation of $\beta$ -catenin
D) Activation of Tcf

Question 50

Phosphorylation of G protein-coupled receptors by GRK

A) turns off G protein signaling.
B) hypersensitizes G protein signaling.
C) blocks the dissociation of the G protein from the receptor.
D) inhibits the GTPase activity of the alpha subunit of the G protein.

Question 51

How would inhibition of PI 3-kinase affect ERK activity in a growth
Factor-stimulated cell?

A) ERK activity would be inhibited.
B) ERK activity would be unaffected.
C) ERK activity would be upregulated.
D) ERK protein would be targeted for destruction by proteolysis.

Question 52

The region of a gene that binds to a PKA phosphorylated protein is a _______.

Question 53

The ras gene is mutant in about 25% of all human cancers. When ras is mutant, it typically remains active in mitogenic signal transduction because it is unable to _______ GTP.

Question 54

The protein kinase Raf phosphorylates the protein kinase _______, which then phosphorylates (on both threonine and tyrosine residues) _______.

Question 55

Key targets of the JAK kinases are _______ proteins.

Question 56

The phosphorylated ERK kinase moves into the nucleus and phosphorylates the transcription factor _______, which binds to serum response elements in a complex with _______ and turns on a set of genes called the _______ genes.

Question 57

Expression of the immediate early genes triggers the expression of a battery of other downstream genes called _______.

Question 58

In animal cells, the common growth factor, or mitogen-activated protein kinase signaling pathway, starts with phosphorylation of tyrosines on the cytosolic domains of the receptor by a process called _______.

Question 59

The extensive crosstalk between individual signal transduction pathways means that multiple pathways interact with one another to form _______ within the cell.

Question 60

_______ refers to the interaction of one signaling pathway with another and integrates the activities of different pathways within the cell.

Question 61

Signaling molecules that activate cell surface receptors are essentially the same as those that activate intracellular receptors.

Question 62

Intracellular signaling pathways provide multiple opportunities for the amplification of a response to an extracellular signal.

Question 63

Binding of integrins to the extracellular matrix stimulates the FAK protein-tyrosine kinase.

Question 64

Many cancers arise as a result of a breakdown in signaling pathways that control cell proliferation.

Question 65

Ras activation is mediated by guanine nucleotide exchange factors (GEFs) that stimulate the release of bound GDP and its exchange for GTP.

Question 66

TGF- $\beta$ signaling leads to the activation of the Smad family of transcription factors.

Question 67

NF- $\kappa$ B activates the gene for I $\kappa$ B, which feeds back and inhibits NF- $\kappa$ B activity.

Question 68

The binding of Hedgehog to the receptor Patched releases a transcription factor from actin microfilaments that enters the nucleus and turns on genes.

Question 69

Notch is a cell-surface receptor protein that activates transcription when a piece of the Notch molecule is cleaved, enters the nucleus, and activates genes.

Question 70

Wnt is a signal molecule that binds to Frizzled/LRP, activating Dishevelled to inhibit a protein kinase. This results in longer lived $\beta$ -catenin, which enters the nucleus and turns on target genes.

Question 71

In signaling pathways, the duration of a single activated pathway (for example, short versus long periods of time) often leads to completely different cellular responses.

Question 72

$\beta$ -arrestin binds to phosphorylated G protein-coupled receptors, binding Raf, MEK, and ERK into the complex and linking the G protein-coupled signal pathway to the ERK signal pathway. This is an example of inhibitory crosstalk.

Question 73

Why is it important that neurotransmitters receptors be located on the external surface of cells?

Question 74

In glucocorticoid signaling, what would happen if Hsp90 was mutated such that it was always bound to the glucocorticoid receptor (GR)?

Question 75

Caffeine is a phosphodiesterase inhibitor. What affect would caffeine treatment have on cells growing in culture?

Question 76

In the absence of cAMP, what is the status of protein kinase A?

Question 77

How would a mutation in CREB that prevents its phosphorylation affect cAMP signaling?

Question 78

What is the family of receptors for most growth factors?

Question 79

What are the three steps by which receptor tyrosine kinases typically convey an extracellular signal to another intracellular enzyme?

Question 80

Describe three features shared by protein-tyrosine kinase growth factor receptors.