AP BIOLOGY

Detailed explanation-1: -A molecule that binds to a receptor is called a ligand and can be a protein, peptide (short protein), or another small molecule, such as a neurotransmitter, hormone, pharmaceutical drug, toxin, calcium ion or parts of the outside of a virus or microbe.

Detailed explanation-2: -Cell-surface receptors come in three main types: ion channel receptors, GPCRs, and enzyme-linked receptors. When a ligand binds an ion channel receptor, a channel through the plasma membrane opens that allows specific ions to pass through.

Detailed explanation-3: -There are three general categories of cell-surface receptors: ion channel-linked receptors, G-protein-linked receptors, and enzyme-linked receptors.

Detailed explanation-4: -A ligand is a molecule that binds another specific molecule, in some cases, delivering a signal in the process. Ligands can thus be thought of as signaling molecules. Ligands interact with proteins in target cells, which are cells that are affected by chemical signals; these proteins are also called receptors.