In the beta-adrenergic receptor system: the adenylyl cyclase is activated by the

Question

In the beta-adrenergic receptor system: the adenylyl cyclase is activated by the heterotrimeric G proteins the heterotrimeric G proteins are integral membrane proteins O cAMP-dependent protein kinase is an integral membrane protein the heterotrimeric G proteins are anchored and travel in the plane of the membrane D Question 3 1 pts Mechanisms that terminate the b-adrenergic response include: binding of adenlyl cyclase to GDP O covalent modification of the receptor to increase its Kd for epiniphrine the presence of cyclic nucleotide phosphodiesterase in the cytoplasm of the ce ll

Explanation / Answer

The beta-adrenergic receptors belong to the family of G-protein coupled receptors. Their activity is regulated by factors that control their ability to bind to and hydrolyze guanosine triphosphate (GTP) to guanosine diphosphate (GDP). When they are bound to GTP, they are 'on', and, when they are bound to GDP, they are 'off'. G proteins belong to the larger group of enzymes called GTPases. There are two classes of G proteins. The first function as monomeric small GTPases, while the second function as heterotrimeric G protein complexes. The latter class of complexes is made up of alpha (), beta () and gamma () subunits.

The receptor-channel complex is coupled to the Gs G protein, which activates adenylyl cyclase, catalysing the formation of cyclic adenosine monophosphate (cAMP) which then activates protein kinase A, and counterbalancing phosphatase PP2A.

Therefore, option A is correct.

The Gs alpha subunit slowly catalyzes the hydrolysis of GTP to GDP, which in turn deactivates the Gs protein, shutting off the cAMP pathway. therefore option A is correct

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