Final answer:
A ligand binds to an ion channel to open its gate, allowing specific ions to pass through and alter the cell's charge. This process typically involves ligand-gated channels, also known as ionotropic receptors, like those activated by neurotransmitters in the nervous system.
Step-by-step explanation:
Typically, the gate of an ion channel remains closed until a ligand binds to the receptor. Ion channels, particularly ligand-gated channels, open when a signaling molecule, or ligand, attaches to the extracellular region of the channel. This interaction is a key feature of ionotropic receptors, such as the neurotransmitter receptors in nerve cells. When the ligand binds to these receptors, it results in a conformational change that opens the channel and allows specific ions to pass through the cell membrane, altering the cell's charge.
For example, when the neurotransmitter acetylcholine binds to its receptor, it triggers the pore within the ligand-gated channel to open, permitting cations like sodium, calcium, and potassium to flow into or out of the cell. These ion channel-linked receptors have unique membrane-spanning regions lined with hydrophobic amino acids to interact with the membrane's center, and hydrophilic amino acids lining the inside of the channel to permit ion passage. As a result, a variety of ions can pass through once the gate is open, significantly impacting cellular activity.