Advanced Placement (AP) Biology 2025 – 400 Free Practice Questions to Pass the Exam

The tyrosine kinase receptor pathway is characterized by the presence of membrane-spanning proteins that have enzymatic activity. In this pathway, the receptors function as protein kinases, which means they are capable of adding phosphate groups to tyrosine residues on specific target proteins within the cell.

When a signaling molecule, such as a growth factor, binds to the extracellular domain of a tyrosine kinase receptor, this triggers the receptor's dimerization (pairing with another identical receptor) and subsequent autophosphorylation. This phosphorylation leads to a conformational change that activates the receptor's intracellular kinase domain. The phosphorylated tyrosine residues serve as docking sites for downstream signaling molecules that can then initiate various cellular responses, such as cell growth, division, or differentiation.

This mechanism is distinct from the other pathways mentioned, such as G-protein linked receptors or gated ion channels, which do not function directly as enzymes that mediate phosphorylation. Instead, G-protein linked receptors activate G-proteins that then initiate a cascade of effects, while gated ion channels primarily facilitate the passage of ions across the membrane without enzymatic activity. The intracellular receptor pathway involves receptors that reside in the cytoplasm or nucleus, binding to signaling molecules and acting as