Tadpoles must undergo a major metamorphosis to become frogs. This change includes reabsorption of the tail, growth of limbs, calcification of the skeleton, increase in rhodopsin in the eye, development of lungs, change in hemoglobin structure, and reformation of the gut from the long gut of an herbivore to the short gut of a carnivore. Amazingly, all of these changes are induced by thyroxine. What is the most likely explanation for such a wide array of effects of thyroxine?

#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 1. Molecules and their Interaction Relevant to Biology

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

#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

#Question id: 1233

#Unit 4. Cell Communication and Cell Signaling

Transphosphorylation (cross-phosphorylation) of receptor tyrosine kinases

a. inhibits catalytic activity.

b. promotes transphosphorylation of additional tyrosine residues.

c. triggers release of the ligand.

d. generates binding sites for signaling molecules.