What type of protein allows a cell to recognize specific substances?

Receptor proteins play a crucial role in cell communication by allowing cells to recognize and respond to specific substances, such as hormones and neurotransmitters. These proteins are typically embedded in the cell membrane and have specific binding sites that are complementary in shape to the signaling molecules they recognize. When a signaling molecule binds to a receptor protein, it can trigger a series of cellular responses, influencing processes such as gene expression, metabolism, and cell growth.

Structural proteins, while important for maintaining the shape and integrity of cells and tissues, do not have the specific binding properties that allow for recognition of substances. Transport proteins are responsible for moving substances across cell membranes but do not typically engage in the recognition processes that receptor proteins do. Enzymes facilitate biochemical reactions but do not function in recognition; their role is largely related to catalyzing reactions rather than identifying and binding to specific molecules. Thus, receptor proteins are distinctly recognized for their ability to enable cells to detect and react to particular substances in their environment.