AP BIOLOGY

Detailed explanation-1: -When a signaling molecule binds to its receptor, it alters the shape or activity of the receptor, triggering a change inside of the cell. Signaling molecules are often called ligands, a general term for molecules that bind specifically to other molecules (such as receptors).

Detailed explanation-2: -When a ligand binds an ion channel receptor, a channel through the plasma membrane opens that allows specific ions to pass through. This process requires a specialized membrane-spanning region of the receptor.

Detailed explanation-3: -When a ligand binds to a protein, it undergoes a conformational change which in turn leads to a physiological response. The time a ligand spends attached to a receptor or specific protein is a function of the affinity between the ligand and the protein.

Detailed explanation-4: -Upon activation by a ligand, the receptor binds to a partner heterotrimeric G protein and promotes exchange of GTP for GDP, leading to dissociation of the G protein into and subunits that mediate downstream signals. GPCRs can also activate distinct signaling pathways through arrestins.