Which term best describes the two essential stages of receptor signaling after ligand binding?

• A. Recognition and transduction
• B. Translation and replication
• C. Hydrolysis and oxidation
• D. Diffusion and osmosis

Answer: (A)

The two stages described are recognition and transduction. Recognition is the specific binding of the ligand to its receptor, forming a receptor-ligand complex due to complementary shapes and chemical interactions. Transduction follows as this binding event is converted into an intracellular signal—often through conformational changes, activation of secondary messengers, and a signaling cascade that leads to a cellular response. In contrast, translation and replication are genetic processes, not parts of receptor signaling; hydrolysis and oxidation are general chemical reactions not specific signaling steps; and diffusion and osmosis describe physical transport across membranes rather than how a signal is translated into cellular action.