Answer:
on the extracellular side of the cell membrane
Explanation:
Ligands can be defined as signaling molecules that interact with receptors localized on target cells. Protein ligands are generally polar and soluble in water. In consequence, they tend to bind with extracellular domain receptors localized on the cell surface, on the outside surface of the cell. Some examples of protein ligands include, among others, hormones (e.g., insulin), growth factors, neurotransmitters, etc.
