Final answer:
The statement about receptor tyrosine kinases (RTKs) dimerizing and cross-phosphorylating the opposite dimer through autophosphorylation upon ligand binding is true. This initiates a downstream cellular response, which is eventually terminated by a phosphatase.
So option (A) is correct.
Step-by-step explanation:
The statement that on recognizing a signal, RTKs dimerize and cross-phosphorylate the opposite dimer via autophosphorylation is true. Receptor tyrosine kinases (RTKs) are critical components in cellular signaling pathways. Upon binding with a signaling molecule, such as a growth factor or hormone, the extracellular domain of the RTKs binds to the signaling molecule which then triggers the dimerization of the receptors. This dimerization facilitates the cross-phosphorylation of tyrosine residues within the intracellular domain of the opposite dimer. As a result, these phosphorylated tyrosine residues become active docking sites for other signaling proteins, thus initiating a cascade of events that leads to a downstream cellular response. The phosphorylation signal is eventually terminated by phosphatase activity, which dephosphorylates the phosphotyrosine residues. This interaction exemplifies the mechanism by which RTKs transduce extracellular signals into specific cellular responses.