Final answer:
Enzyme-linked receptors are cell-surface receptors associated with an enzyme. When a ligand binds to the extracellular domain, it activates the enzyme, leading to a cascade of cellular events.
Step-by-step explanation:
Enzyme-linked receptors are cell-surface receptors with intracellular domains that are associated with an enzyme. When a ligand binds to the extracellular domain, a signal is transferred through the membrane, activating the enzyme. One example of this type of enzyme-linked receptor is the tyrosine kinase receptor. First, signaling molecules bind to the extracellular domain of two nearby tyrosine kinase receptors. The two neighboring receptors then bond together, or dimerize. Phosphates are then added to tyrosine residues on the intracellular domain of the receptors (phosphorylation). The phosphorylated residues can then transmit the signal to the next messenger within the cytoplasm.