Receptor proteins are specialized molecules located on the surface of cells or within them. They play a crucial role in cell communication by binding to specific signaling molecules, such as hormones or neurotransmitters. This binding triggers a series of cellular responses, allowing the cell to react to changes in its environment. These proteins are essential for various biological processes, including immune response, nervous system function, and cell growth. Different types of receptor proteins exist, such as G-protein coupled receptors and ion channel receptors, each with unique functions and mechanisms of action.