Final answer:
Receptors respond to polar regulatory molecules by opening or closing ion channels or activating enzymes. The binding of a ligand to a receptor triggers a cascade of events inside the cell, leading to various cellular responses including gene activation and enzyme activity modifications. Cyclic AMP, as a second messenger, plays a critical role in these signaling processes.
Step-by-step explanation:
Receptors are molecules that initially respond to polar regulatory molecules by opening/closing membrane ion channels or by activating enzymes, such as those that produce cyclic AMP (CAMP). Cell signaling pathways start with the binding of a ligand to a receptor, which can be a membrane receptor protein or an internal receptor. Polar ligands typically interact with membrane receptors, leading to the opening or closing of ion channels or activating a G-protein that then triggers a series of reactions inside the cell, often involving the production of second messengers such as CAMP or IP3.
The activation of enzymes like adenylate cyclase by G-proteins results in the production of CAMP, which activates protein kinases through a phosphorylation cascade. These events cause various cellular responses, including changes in metabolic processes, gene activation, and protein synthesis. These mechanisms are crucial for cellular communication and can lead to long-term changes in the cell, such as those involved in learning and memory.