Receptor proteins are specialized molecules located on the surface of cells that play a crucial role in communication between cells and their environment. They bind to specific substances, such as hormones or neurotransmitters, triggering a response within the cell. This process is essential for various biological functions, including growth, immune responses, and metabolism. When a receptor protein binds to its target molecule, it undergoes a change in shape, which activates a series of cellular processes. This interaction is vital for maintaining homeostasis and allowing cells to respond to changes in their surroundings, ensuring proper functioning of the body as a whole.