Question

question 21 (1 point) typically, the gate of an ion channel remains closed until a(n) ____ binds to the receptor. ligand target cell g protein first messenger enzyme

Explanation:

Ion - channel gating can be ligand - gated. When a ligand binds to the receptor associated with the ion channel, it can cause a conformational change that opens the channel. Target cells are not directly involved in this gating mechanism by binding to the receptor. G - proteins are involved in some signaling pathways but not the direct binding to open ion - channel gates. First messengers can initiate signaling but do not directly bind to open ion - channel gates in the way a ligand does. Enzymes are not the molecules that bind to open ion - channel gates.

Answer:

A. ligand