Enzyme-linked receptors are a type of cell surface receptor that, upon binding to a specific ligand, activate an intrinsic enzymatic activity. These receptors typically have a single transmembrane domain and can function as enzymes themselves or associate with other proteins that have enzymatic activity. A common example is the receptor tyrosine kinase, which phosphorylates tyrosine residues on target proteins, leading to various cellular responses. When a ligand, such as a growth factor, binds to the enzyme-linked receptor, it triggers a conformational change that activates the receptor's enzymatic function. This activation initiates a cascade of signaling events within the cell, influencing processes like cell growth, differentiation, and metabolism. The precise regulation of these pathways is crucial for maintaining normal cellular functions and responding to external signals.