Module 10

Question 1

The KD or dissociation constant between a receptor and its ligand is

Answer 1

both a measure of the binding affinity the receptor has for the hormone and the hormone concentration where half the receptors are bound to hormone.

Question 2

Which of the following order of events is most accurate for activation of G-protein coupled receptor (GPCR) signaling pathways?

Answer 2

Hormone binds GPCR, GPCR binds with G protein, G protein loses GDP and gains GTP, G-protein alpha subunit activates intracellular proteins.

Question 3

Following its initial activation, how does a G protein become inactivated?

Answer 3

The G-protein α subunit GTP is hydrolyzed to GDP allowing reassociation of the G-protein α subunit and βγ dimer.

Question 4

Adenylyl cyclase is to cAMP as ________ is to IP3.

Answer 4

phospholipase C

Question 5

Which of the following is likely involved in calcium signaling?

Answer 5

IP3
calmodulin
protein kinase C
phospholipase C

Question 6

A hormone binds a receptor and activates the cAMP signal transduction pathway ultimately leading to the cell response. Which of the following is NOT a likely mechanism for downregulating cAMP transduction?

Answer 6

Activate adenylyl cyclase.

Question 7

A hormone binds a receptor and activates the cAMP signal transduction pathway ultimately leading to the cell response. Which of the following is a likely mechanism for downregulating cAMP transduction?

Answer 7

The hormone dissociating from the receptor.
The GTP on the alpha subunit of the G protein is hydrolyzed to GDP.
Activate phosphodiesterase.
Protein phosphatases remove phosphates from proteins initially activated by protein kinase A

Question 8

Protein kinase A (PKA) is:

Answer 8

allosterically activated by cyclic AMP.

Question 9

Diacylglycerol (DAG) activates :

Answer 9

protein kinase C

Question 10

Which of the following events occur(s) during the hormone-stimulated conversion of glycogen to glucose-1-phosphate?

Answer 10

activation of beta-adrenergic receptor upon binding to epinephrine.
Activation of PKA upon binding to cAMP
inhibition of glycogen synthase
activation of glycogen phosphorylase

Question 11

The activity of β-adrenergic receptors may be regulated by

Answer 11

Phosphorylation by β-adrenergic receptor kinase (BARK).
Homologous desensitization
Heterologous desensitization
Intracellular sequestration of the receptor

Question 12

The cholera toxin causes profuse diarrhea because it

Answer 12

modifies a G protein involved in regulating salt and water secretion.

Question 13

Which of the following is the best explanation for the fact that most transduction pathways have multiple steps?

Answer 13

Multiple steps provide for greater possible amplification of a signal.

Question 14

Phosphodiesterase activity is involved in the regulation of signal transduction because it

Answer 14

converts cGMP to GMP.

Question 15

A major group of G protein-coupled receptors contains seven transmembrane α helices. The amino end of the protein lies at the exterior of the plasma membrane. Loops of amino acids connect the helices either at the exterior face or on the cytosol face of the membrane. The loop on the cytosol side between helices 5 and 6 is usually substantially longer than the others. The coupled G protein most likely interacts with this receptor

Answer 15

at the carboxyl terminal end, the loop between H5 and H6 and other cytosol-facing loops.

Question 16

Lipid-soluble signaling molecules, such as testosterone, can cross the membranes of all cells but they affect and produce a response only in certain target cells. This may be because

Answer 16

intracellular receptors that recognize and bind to testosterone are present only in target cells.

Question 17

What type of receptor does IP3 bind?

Answer 17

ligand-gated Ca2+ channel

Question 18

In paracrine signaling:

Answer 18

Cells release a signal that affects neighboring cells.

Question 19

The G-protein involved in visual signal transduction is:

Answer 19

transducin``

Question 20

Elevated epinephrine levels do normally stimulate:

Answer 20

fatty acid mobilization in adipose tissue.
glycogen breakdown in liver.
glycogen breakdown in muscle.
glycolysis in muscle.