Final answer:
When indirect signaling is used, the target cell responds when a chemical binds to a receptor on the cell surface. In the case of adenylyl cyclase inhibition, the synthesis of cAMP would be blocked in the G-protein signaling pathway. Lipid-soluble molecules like thyroid hormone can bind to internal receptors and directly impact gene expression.
Step-by-step explanation:
When indirect signaling is used, the target cell responds to the signal when that chemical binds to a receptor. The receptors are specific proteins that recognize and bind to signaling molecules, known as ligands. Once the ligand binds to the receptor, it triggers a cellular response which can involve a variety of mechanisms including the activation of enzymes, opening of ion channels, or changes in gene transcription.
Accordingly, if a chemical is an inhibitor of the enzyme adenylyl cyclase, the following step in the G-protein signaling pathway would be blocked: d. synthesis of CAMP. This is because adenylyl cyclase is responsible for converting ATP to cyclic AMP (cAMP), which acts as a second messenger in various signaling pathways.
It's important to note that thyroid hormone is a lipid-soluble signal molecule that can cross the membrane of all cells. It would not require a membrane receptor to exert its effects; instead, it can bind to internal receptors and directly influence gene expression in the target cell.