Which of the following events contributes to the termination of a signal generated by the binding of a ligand to a receptor tyrosine kinase? Only one answer is correct 1. Phosphatases hydrolyze key phosphorylated residues.
2. Kinases hydrolyze key phosphorylated residues.
3. Kinases phosphorylate key residues.
4. The receptor tyrosine kinase dimerizes.
5. GTPase removes a phosphoryl group from GTP.
6. Phosphatases phosphorylate key residues.

1. Phosphatases hydrolyze key phosphorylated residues.

Explanation:

Receptor Tyrosine Kinases (RTKs) are high-affinity transmembrane protein receptors that bind to a wide variety of ligands (e.g., growth factors, cytokines, hormones). These receptors (RTKs) have a transmembrane domain and therefore these proteins act as membrane receptors, as well as exhibit catalytic activity. The intracellular C terminal region of RTKs contains catalytic domains responsible for both autophosphorylation and tyrosine phosphorylation of their protein substrates. Moreover, Protein Tyrosine Phosphatase (PTPs) are critical enzymes that remove phosphate groups from tyrosine residues in different substrates (including RTKs), thereby regulating key signaling pathways such as cell proliferation, cell differentiation, and cell-cell adhesion.

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