A newly discovered signaling molecule that binds to a G protein-coupled receptor is being studied by using cells maintained in cell culture. Preliminary results show that the binding of this new ligand causes the activation of adenylyl cyclase. In the next part of this study, a non-hydrolyzable version of GTP (a form of GTP that cannot be converted to GDP) is added to the cell culture dishes and is taken up by the cells. Which of the following would you expect to observe?
A)increased cAMP, decreased protein kinase A activity
B)decreased cAMP, decreased protein kinase A activity
C)decreased cAMP, increased protein kinase A activity
D)increased cAMP, increased protein kinase A activity

Question

Quizplus · Accepted Answer

A non-hydrolyzable version of GTP would lock the G protein in its active state, thus continuously stimulating adenylyl cyclase to produce more cAMP. This results in increased cAMP levels, which in turn activates protein kinase A. Therefore, addition of non-hydrolyzable GTP would result in increased cAMP and increased protein kinase A activity.

A Newly Discovered Signaling Molecule That Binds to a G