The upper forelimbs of humans and bats have fairly similar skeletal structures, whereas the corresponding bones in whales have very different shapes and proportions. However, genetic data suggest that all three kinds of organisms diverged from a common ancestor at about the same time. Which of the following is the most likely explanation for these data?

#Question id: 1126

#Unit 4. Cell Communication and Cell Signaling

Which of the following statement(s) is (are) true of the α subunit of a G protein?

a. It physically associates with the receptor.              

b. It binds GDP.

c. It binds GTP.                     

d. It is a transmembrane protein.

#Question id: 1127

#Unit 4. Cell Communication and Cell Signaling

Which of the following steps does not occur after acetylcholine binds to the muscarinic acetylcholine receptor in heart muscle cells?

#Question id: 1128

#Unit 4. Cell Communication and Cell Signaling

During the epinephrine stimulated conversion of glycogen to glucose 1-phosphate, which of the following steps involves protein phosphorylation?

a. inactivation of glycogen synthase               b. activation of protein kinase A

c. activation of adenylyl cyclise                      d. activation of glycogen phosphorylase

#Question id: 1129

#Unit 4. Cell Communication and Cell Signaling

Which of the following plays a role in the relaxation of smooth muscle cells by nitric oxide?

a. cGMP          b. protein kinase A      c. protein kinase G      d. guanylyl cyclise

#Question id: 1130

#Unit 4. Cell Communication and Cell Signaling

In muscle cells, glycogen phosphorylase kinase is activated by

a. Ca2+.           b. diacylglycerol.   c. nitric oxide.       d. protein kinase A.    

#Question id: 1131

#Unit 4. Cell Communication and Cell Signaling

Which of the following function(s) as an inhibitor of TGFβ signal transduction?

a. R-Smad       b. I-Smad        c. Co-Smad     d. Ski   e. SnoN