Our biological processes rely on a system of communications -- cellular signals -- that set off chain reactions in and between target cells to produce a response. The first step in these often complex communications is the moment a molecule binds to a receptor on or in a cell, prompting changes that can trigger further signals that propagate across systems. From food tasting and blood oxygenation during breathing to drug therapy, receptor binding is the fundamental mechanism that unlocks a multitude of biological functions and responses.