The correct sequence of events involved in phototransduction in rods and cones in response to light is:

#Question id: 1227

#Unit 4. Cell Communication and Cell Signaling

Which of the following is a mechanism for down regulation of signaling from G protein-coupled receptors?

a. a change in the Kd of the receptor-hormone complex

b. proteolysis of the Gα subunit                     

c. hydrolysis of cAMP to 5´-AMP

d. dephosphorylation of adenylyl cyclase

#Question id: 1228

#Unit 4. Cell Communication and Cell Signaling

Place the events that follow the binding of a ligand to a G protein-coupled receptor that acts on adenylyl cyclase in the correct order:

a. GTP is hydrolyzed to GDP.           

b. GDP is displaced from Gα.           

c. the Gα-GTP complex dissociates from the Gβγcomplex.  

d. GTP is bound to Gα. 

#Question id: 1229

#Unit 4. Cell Communication and Cell Signaling

Which of the following events occur(s) during light activation of the rhodopsin receptor?

a. 11-cis-retinal is converted to all-trans-retinal

b. activation of the trimeric G protein, transducin

c. activation of cGMP phosphodiesterase

d. opening of the cGMP-gated ion channel

#Question id: 1230

#Unit 4. Cell Communication and Cell Signaling

Which of the following events occur(s) following the binding of a ligand to a G protein–coupled receptor that triggers release of Ca2+?

a. activation of protein kinase A by IP3

b. phospholipase cleavage of PIP2 to IP3 and DAG

c. release of DAG into the cytosol

d. IP3-mediated opening of Ca2+ channels in the ER membrane

#Question id: 1231

#Unit 4. Cell Communication and Cell Signaling

Arrange the following events in the proper order in which they occur during transduction of the TGFβ signal:

a. association of Smad3 and Smad4  

b. phosphorylation of TGFβ receptor I by TGFβ receptor II            

c. phosphorylation of Smad3 by TGFβ receptor I     

d. nuclear import of Smad3   

e. binding of TGFβ to TGFβ receptor II  

#Question id: 1232

#Unit 4. Cell Communication and Cell Signaling

Which of the following mutations might confer a competitive advantage to an athlete by raising his or her hematocrit?

a. excess production of erythropoietin                       

b. decreased production of erythropoietin

c. EpoR that cannot bind STAT5                  

d. EpoR that cannot bind SHP1

e. EpoR that cannot bind JAK2