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Tyrosine kinase receptors are a class of cell surface receptors that play a crucial role in cell signaling. They are a type of transmembrane protein that possesses intrinsic enzymatic activity. Specifically, they can phosphorylate tyrosine residues on other proteins, a process known as tyrosine phosphorylation. This phosphorylation acts as a molecular switch, initiating a cascade of downstream signaling events that regulate a wide array of cellular functions. These functions include cell growth, differentiation, metabolism, and survival.

The activation of tyrosine kinase receptors typically occurs when an extracellular ligand, such as a growth factor or hormone, binds to the receptor's extracellular domain. This binding induces a conformational change in the receptor, leading to dimerization or oligomerization of receptor subunits. This close proximity allows the intracellular tyrosine kinase domains to phosphorylate each other on specific tyrosine residues, a process called autophosphorylation. These phosphorylated tyrosine residues then serve as docking sites for various intracellular signaling molecules, including adaptor proteins, enzymes, and transcription factors.

These recruited signaling molecules are then activated, initiating complex signaling pathways like the Ras/MAPK pathway, the PI3K/Akt pathway, and the JAK/STAT pathway. These pathways ultimately transmit the signal to the nucleus, influencing gene expression and altering cellular behavior. Dysregulation of tyrosine kinase receptor signaling is implicated in numerous diseases, most notably cancer, where uncontrolled cell proliferation and survival are often driven by aberrant receptor activation. Consequently, tyrosine kinase inhibitors have become a significant class of targeted therapies in oncology.