Final answer:
Drug-receptor binding is a specific interaction where a drug molecule physically interacts with a cell's receptor, which can activate ion channels or signal transduction pathways. Dopamine binding to a G-protein-linked receptor increases cAMP concentration. An agonist drug mimics a neurotransmitter by binding to its receptor and eliciting a response.
Step-by-step explanation:
Drug-receptor binding occurs through a highly specific interaction where a drug molecule binds to a receptor, which is a protein on the surface of a cell. This process is akin to a key entering a lock - the drug acts as the key and the receptor is the lock. The unique molecular structure of the drug complements the receptor's shape, allowing for a physical interaction. This interaction can lead to various cellular responses, including the activation of ion channels or signal transduction pathways that can involve second messengers like cyclic AMP (cAMP).
Neurotransmitters, such as dopamine, are natural substances that also bind to receptors. When dopamine binds to its G-protein-linked receptor, we expect an increase in the concentration of cAMP, as this is a common second messenger involved in the signaling pathway activated by dopamine.
Similarly, a drug can act as an agonist if it mimics the action of a neurotransmitter by binding to the same receptor and eliciting a response. Drugs can affect the neurotransmitter system by interacting with their receptors, either to block them, activate them, or alter the reuptake of neurotransmitters like in the case of some antidepressants. This profoundly affects neurotransmission and can modify the synaptic transmission which plays a critical role in communication between neurons.