Final answer:
Nicotine binds to specific sites on the heteromeric nicotinic receptor, a ligand-gated ion channel, resulting in increased neuron activity and dopamine release.
Step-by-step explanation:
Nicotine specifically binds to the nicotinic receptor, a type of acetylcholine receptor protein. This receptor is heteromeric, meaning it consists of multiple subunits that form a ligand-gated ion channel. When nicotine binds to these receptors, it causes the channel to open, allowing cations, such as Na+ and Ca2+, to flow into the neuron. This action can excite the neuron, resulting in the increased firing of action potentials and enhanced neurotransmitter release, such as dopamine. For example, in the presynaptic neuron, nicotine stimulates the neuron to release more dopamine, impacting functions like attention, reward mechanisms, and motor control.
In relation to binding sites, the nicotine molecule interacts with the receptor at specific binding interfaces between the subunits of the heteromeric receptor complex. Within these interfaces, the complementary shapes and charge distributions of the nicotine and the receptor's binding site allow for this specific interaction, analogous to a lock and key mechanism.