Question 1

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

Accepted Answer

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 
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 D

Question 2

In trimeric G proteins,GTP binds to:

Accepted Answer

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

Question 3

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?

Accepted Answer

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 
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 C

Question 4

DAG activates:

Accepted Answer

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

Question 5

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?

Accepted Answer

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 
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 6

In paracrine signaling,the signaling molecule:

Accepted Answer

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. 
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 7

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

Accepted Answer

The functional domains of G protein-coup

Question 8

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

Accepted Answer

The role of the intrinsic GTPase activit

Question 9

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:

Accepted Answer

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

Question 10

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?

Accepted Answer

The dissociation constant,Kd,is a measur

Question 11

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

Accepted Answer

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. 
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 12

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

Accepted Answer

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

Question 13

The activity of β-adrenergic receptors is regulated by:

Accepted Answer

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

Question 14

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

Accepted Answer

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

Question 15

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

Accepted Answer

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. 
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 16

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

Accepted Answer

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

Question 17

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

Accepted Answer

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 
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 18

Describe the differences between an agonist and an antagonist.

Accepted Answer

Agonists are molecules that mimic the fu

Question 19

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

Accepted Answer

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

Question 20

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:

Accepted Answer

A) Gαq. 
B) Gαs. 
C) Gαi. 
D) Gαo. 
A) Gαq. 
B) Gαs. 
C) Gαi. 
D) Gαo.

Exam 14: Signal Transduction and G-Protein Coupled Receptors

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

In trimeric G proteins,GTP binds to:

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?

DAG activates:

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?

In paracrine signaling,the signaling molecule:

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

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

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 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?

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

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

The activity of β-adrenergic receptors is regulated by:

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

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

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

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

Describe the differences between an agonist and an antagonist.

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

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:

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