A signaling cell releases a small molecule that binds a specific protein on a target cell and delivers a signal. What is this released molecule called?

1. A ligand is defined as a molecule that binds another specific molecule and can deliver a signal in the process. 2. Ligands are released by signaling cells and interact with proteins called receptors on target cells. 3. A receptor is the protein that the ligand binds, not the signal itself, so it does not fit the description. 4. Kinases and phosphatases are enzymes that act later in a signaling pathway, not the initial released signal. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 9 "Cell Communication", section 9.1 Signaling Molecules and Cellular Receptors_