This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General physiology, Subject name: Physiology
Adenylyl cyclase is associated with 
Select and explain. 
A. GABA-a, B. Seven transmembrane domain receptors or GPCR, C. Cholinergic receptor, D. Glycine receptor
B: Seven transmembrane domain receptors or GPCR
Answer: B: Seven transmembrane domain receptors or GPCR 
Explanation: Adenylyl cyclase is a transmembrane protein, and it crosses the membrane 12 times. Ten isoforms of this enzyme have been described and each can have distinct regulatory propeies, permitting the cAMP pathway to be customized to specific tissue needs. Notably, stimulatory heterotrimeric G proteins (Gs) activate, while inhibitory heterotrimeric G proteins (Gi) inactivate adenylyl cyclase (Figure 2-28). When the appropriate ligand binds to a stimulatory receptor, a Gs a subunit activates one of the adenylyl cyclases.(Ref: Ganong&;s review of medical physiology 23rd edition Page no: 56)