Final answer:
At metabotropic receptors, a neurotransmitter binding to a receptor stimulates a G-protein, which then activates a second messenger through enzymatic actions. Neurotransmitter binding to a receptor at metabotropic receptors does not directly open or close channels that are part of the same or separate protein as the receptor. Instead, it triggers intracellular signaling pathways.
Step-by-step explanation:
Neurotransmitters bind to one of two classes of receptors at the cell surface: ionotropic or metabotropic. Ionotropic receptors are ligand-gated ion channels, while metabotropic receptors involve a complex of proteins that result in metabolic changes within the cell. At metabotropic receptors, a neurotransmitter binding to a receptor stimulates a G-protein, which then activates a second messenger through enzymatic actions.
The receptor complex at metabotropic receptors includes the transmembrane receptor protein, a G protein, and an effector protein. The neurotransmitter, referred to as the first messenger, binds to the receptor protein on the extracellular surface of the cell, and the intracellular side of the protein initiates activity of the G protein. The G protein physically moves from the receptor protein to the effector protein to activate the latter. The effector protein, an enzyme, catalyzes the generation of a second messenger that acts as the intracellular mediator of the signal that binds to the receptor.
Neurotransmitter binding to a receptor at metabotropic receptors does not directly open or close channels that are part of the same or separate protein as the receptor. Instead, it triggers intracellular signaling pathways that lead to various cellular responses.