Final answer:
Receptors are crucial for cell communication, acting as protein molecules that bind with ligands to initiate a series of intracellular events.
Step-by-step explanation:
Receptors are protein molecules in the target cell or on its surface that bind to ligands, initiating a cascade of events within the cell. There are two types of receptors:
- Internal receptors, also known as intracellular or cytoplasmic receptors, are located in the cytoplasm and respond to hydrophobic ligand molecules that cross the plasma membrane.
- Cell-surface receptors span the plasma membrane and convert extracellular signals into intracellular signals via signal transduction.
Once a ligand binds to the receptor, it initiates signal transduction throughout the cell, often involving the phosphorylation or generation of second messengers.