Deck 14: Signal Transduction and G-Protein Coupled Receptors

Question 1

Phosphatidylinositol 4,5-bisphosphate (PIP₂)is cleaved by phospholipase C into:

A)1,2-diacylglycerol (DAG).
B)phosphatidylinositol (PI).
C)inositol 1,4,5-trisphosphate (IP₃).
D)1,2-diacylglycerol (DAG)and inositol 1,4,5-trisphosphate (IP₃).

Answer 1

D

Question 2

Pull-down assays using proteins that ONLY bind to the GTP-bound version of the small G-protein can be used to detect when small G proteins like Rac1 have been activated by various growth factors.You were given two lysates,one having been treated with platelet-derived growth factor (PDGF)and the other not treated with PDGF.This method is similar to performing co-IPs,so based on that knowledge,which of the following steps is erroneous?

A)To assay for levels of active Rac1,PAK1-beads (the protein that only binds GTP-bound Rac1-conjugated to beads similar to Nickel beads)are added to each of the lysates described above and incubated on a rocking platform (on ice).
B)The tubes are vortexed well,loading buffer is added,and the samples are heated to aid in protein denaturation.
C)The samples are loaded and analyzed by SDS-polyacrylamide gel electrophoresis,then the proteins are transferred to a membrane.
D)The membrane (a.k.a.blot)will be probed with the anti-Rac antibody.

Answer 2

B

Question 3

Of the components of a heterotrimeric G protein,which subunit(s)is(are)able to activate downstream responses?

A)only the alpha subunit
B)only the beta/gamma subunits
C)only the delta subunit
D)both the alpha subunit and the beta/gamma subunits

Answer 3

D

Question 4

Cell sensitivity to an external signal is determined by:

A)kₒn.
B)kₒff.
C)Kd.
D)the number of surface receptors.

Question 5

Phospholipase C is activated by:

A)Gαs.
B)Gαᵢ.
C)Gαq.
D)none of the above

Question 6

Which of the following is NOT a common intracellular second messenger?

A)inositol 1,4,5-trisphosphate (IP₃)
B)1,2 diacylglycerol (DAG)
C)adenosine triphosphate (ATP)
D)3´-5´ cyclic guanine monophosphate (cGMP)

Question 7

In trimeric G proteins,GTP binds to:

A)the α subunit.
B)the β subunit.
C)the γ subunit.
D)the activated trimer.

Question 8

In paracrine signaling,the signaling molecule:

A)acts on cells in close proximity to the secreting cell.
B)acts on target cells far away from the secreting cell.
C)acts on the same cells that secreted the signaling molecule.
D)is carried to the target cells via the circulation.

Question 9

A particular antagonist for an epinephrine-receptor protein is under consideration as a new drug.What values would you use to measure how tightly the drug binds to the target protein compared with epinephrine binding? What technique would you use to measure drug binding?

Question 10

Pull-down assays can be used to detect when small G proteins like Rac1 have been activated by various growth factors.If you were given two lysates,one having been treated with platelet-derived growth factor (PDGF)and the other treated with PDGF that had been heat-inactivated,briefly describe the pull-down assay and what you would expect to see following the assay.

Question 11

1,2-diacylglycerol (DAG)and inositol 1,4,5-trisphosphate (IP3)are cleaved from phosphatidylinositol 4,5-bisphosphate (PIP₂)by the enzyme:

A)adenylyl cyclase.
B)phosphodiesterase.
C)phospholipase C.
D)protein kinase C.

Question 12

Which of the following general statement(s)about a G protein-coupled receptor is (are)TRUE?

A)It contains 12 transmembrane domains.
B)It is positioned with the N-terminus on the cytoplasmic face of the membrane.
C)It is positioned with the C-terminus on the cytoplasmic face of the membrane.
D)all of the above

Question 13

Explain the differences between endocrine,paracrine,and autocrine signaling.

Question 14

All the following statement(s)about cholera toxin are TRUE,except:

A)it chemically modifies the Gαs protein.
B)it is a G protein-coupled receptor.
C)it prevents hydrolysis of bound GTP to GDP.
D)it leads to continuous activation of adenylyl cyclase.

Question 15

Summarize the steps in the cycling of GTPase switch proteins from active to inactive states.

Question 16

What experimental approach was used to identify functional domains of G protein-coupled receptors?

Question 17

GTPases serve in many signal transduction pathways and the presence of GTP or GDP dictates whether the pathway is on or off,respectively.Which of the following statements is TRUE regarding guanine nucleotide exchange factors (GEF)and the role in these signaling pathways?

A)They hydrolyze GTP into GDP and Pᵢ.
B)They decrease the GTPase activity of the G-protein.
C)They catalyze the dissociation of GDP on the G-protein and promote the replacement of GTP.
D)none of the above

Question 18

Describe the differences between an agonist and an antagonist.

Question 19

cGMP phosphodiesterase catalyzes the conversion of:

A)cAMP to cGMP.
B)cGMP to 5´-GMP.
C)GTP to cGMP.
D)cGMP to GDP.

Question 20

If [R] = the free receptor concentration and [L] = the free ligand concentration,Kd is:

A)[R]/[L].
B)[L]/[R].
C)[R][L]/[RL].
D)[RL]/[R] [L].

Question 21

β-blockers inhibit an adrenergic receptor found on many cell types in the body,including heart cells.Patients who have arrhythmias (irregular heartbeats)most likely benefit from what downstream action of these drugs?

A)increased frequency of IP3 release
B)activation of PLC
C)increased adenylyl cyclase activity
D)decreasing cAMP-mediated effects on contraction rate

Question 22

The activity of β-adrenergic receptors is regulated by:

A)β-adrenergic receptor kinase (BARK).
B)calmodulin.
C)β-tubulin.
D)all of the above

Question 23

Which of the following is a common step in the opening/closing of ion channels by acetylcholine and rhodopsin binding to their receptors?

A)The Gα·GTP subunit dissociates from the Gβγ complex.
B)The released Gα·GTP subunit interacts with the ion channel.
C)The released Gβγ complex interacts with the ion channel.
D)The released Gα·GTP subunit activates cGMP phosphodiesterase.

Question 24

Which of the following events occur during the epinephrine-stimulated conversion of glycogen to glucose-1-phosphate?

A)activation of PKA by cAMP
B)inhibition of glycogen synthase
C)activation of glycogen phosphorylase
D)all of the above

Question 25

Which enzyme plays a role in regulating rhodopsin-induced closing of cation channels?

A)guanylyl cyclase
B)adenylyl cyclase
C)phosphodiesterase
D guanylyl cyclase and phosphodiesterase

Question 26

Rhodopsin,a light-sensitive GPCR whose role in vision is dependent on its phosphorylation status,is influenced in part by the protein arrestin.Which of the following is TRUE with regard to rhodopsin and vision?

A)Rhodopsin phosphatase increases the degree of rhodopsin phosphorylation.
B)Arrestin binds to the completely phosphorylated opsin to inhibit signaling.
C)Rhodopsin activation promotes the opening of a cGMP-gated ion channel.
D)none of the above

Question 27

The G protein stimulated by light via the Rhodopsin receptor is ____,while the effector is ____.

A)Gαi;sodium channels
B)Gαo;adenylyl cyclase
C)Gαt;PDE
D)Gαq;guanylate cyclase

Question 28

Signal amplification is an important part of GPCR-mediated signaling.Which of the following steps do NOT directly amplify the signal?

A)effector activation
B)binding of second messenger to target protein/ion channel
C)kinase acting on substrates
D)second messenger generation

Question 29

A mutation renders a Gαq subunit constitutively active (also known as dominant active).Which of the following effects might you observe in a cell with this mutation?

A)PIP2 levels in the cell membrane diminish
B)PKC activity decreases
C)IP3 is sequestered at the membrane
D)beta/gamma subunits are less active

Question 30

One form of receptor desensitization can be mediated by negative feedback involving phosphorylation of the receptor itself by a kinase activated downstream of a second messenger.The phosphorylated receptor likely:

A)would be resensitized by a kinase.
B)would activate heterotrimeric G proteins at a faster rate.
C)would be unable to bind ligand.
D)could be resistant to desensitization if Ser/Thr phosphatases were acting on the same receptor,

Question 31

Muscarinic acetylcholine receptors are GPCRs that slow the rate of heart muscle contraction upon ligand binding/activation.Activation of this receptor leads to opening of potassium channels triggered by decreases in cAMP levels.The muscarinic acetylcholine receptor likely couples to:

A)Gαq.
B)Gαs.
C)Gαi.
D)Gαo.

Question 32

Which of the following mechanisms can terminate an intracellular signaling pathway once the concentration of an external signal decreases?

A)degradation of the second messenger
B)desensitization of receptors
C)deactivation of a signal transduction protein
D)all of the above

Question 33

Diacylglycerol (DAG)formation aids in cell signaling by:

A)acting as a substrate for PKC.
B)acting as a soluble second messenger that can directly activate kinases near the nucleus.
C)acting as a specific docking site to activate a downstream kinase.
D)none of the above

Question 34

Which type of experimental evidence shows that the intrinsic GTPase activity of the Gα subunit is important for terminating effector activation?

A)A nonhydrolyzable GTP analog that can bind to the Gα subunit but cannot be hydrolyzed by the intrinsic GTPase,thereby activating the effector protein longer upon ligand-induced activation of the receptor.
B)A nonhydrolyzable GTP analog causes displacement of GDP with the modified GTP resulting in continuous activation of the receptor because the bound GTP analog cannot be hydrolyzed to GDP.
C)A dominant active (constant activity)GEF causes stimulation of the effector protein for longer upon ligand-induced activation of the receptor.
D)A dominant negative (no activity)GEF causes stimulation of the effector protein for longer upon ligand-induced activation of the receptor.

Question 35

How does the body respond to decreases in blood glucose levels below about 5 mM?

Question 36

Cholera toxin can make you sick through overactivation of a Gαs pathway even if your body stops making the ligand associated with activation of the pathway.Knowing this,which of the following CANNOT be true about cholera toxin?

A)It chemically modifies the Gαs protein.
B)Cholera toxin activates a ligand-activated G protein-coupled receptor.
C)It prevents hydrolysis of bound GTP to GDP.
D)It leads to continuous activation of adenylyl cyclase.

Question 37

Describe the proposed mechanism for the opening of K⁺ channels by cardiac muscarinic acetylcholine receptors.

Question 38

Which of the following statements about adenylyl cyclase stimulation/inhibition in adipose cells is TRUE?

A)Prostaglandin E1 stimulates adenylyl cyclase.
B)Glucagon inhibits adenylyl cyclase.
C)Epinephrine stimulates adenylyl cyclase.
D)Glucagon inhibits adenylyl cyclase and epinephrine stimulates adenylyl cyclase.

Question 39

Describe experimental evidence supporting that intrinsic GTPase activity of the Gα subunit is important for terminating effector activation.

Question 40

When the regulatory domain of PKA is bound to cAMP:

A)the released catalytic subunit travels to the nucleus where it can phosphorylate CREB.
B)the catalytic subunit acts on CRE to stimulate gene transcription.
C)the AKAP adaptor protein sequesters the catalytic subunit.
D)PDE is inhibited to cause cAMP levels to rise.

Question 41

DAG activates:

A)PKC.
B)PKA.
C)PLC.
D)calmodulin.

Question 42

After a meal,when blood glucose rises,circulating insulin binds to insulin receptors on various cell types and reduces blood glucose levels by:

A)fusion of intracellular vesicles containing GLUT4 glucose transporters with the plasma membrane.
B)stimulation of the conversion of glucose to glycogen.
C)inhibition of glucose synthesis from smaller molecules.
D)all of the above

Question 43

In muscle,glycogen phosphorylase kinase can be activated by nerve stimulation even in the absence of hormonal signals.Nerve stimulation alone results in activation of glycogen phosphorylase kinase as a result of:

A)elevated cytosolic Ca²⁺.
B)phosphorylation by cAMP dependent PKA.
C)both of the above
D)none of the above

Question 44

Describe the steps in the synthesis of 1,2-diacylglycerol (DAG)and inositol 1,4,5-trisphosphate (IP₃)from phosphatidylinositol (PI).

Question 45

Calmodulin:

A)is a ubiquitous protein in eukaryotic cells.
B)binds Ca²⁺ in a cooperative fashion.
C)is a membrane-bound protein.
D)is a ubiquitous protein in eukaryotic cells that binds Ca²⁺ in a cooperative fashion.