## Phospholipase C and IP₃/DAG Signaling **Key Point:** Phospholipase C (PLC) is the enzyme responsible for cleaving phosphatidylinositol 4,5-bisphosphate (PIP₂) into two critical second messengers: inositol 1,4,5-trisphosphate (IP₃) and diacylglycerol (DAG). ### Mechanism 1. G-protein coupled receptors or receptor tyrosine kinases activate PLC 2. PLC hydrolyzes the phosphodiester bond in PIP₂ 3. Products: IP₃ (soluble, diffuses to ER) and DAG (membrane-bound) ### Downstream Effects | Second Messenger | Location | Action | |---|---|---| | IP₃ | Cytosol | Binds IP₃ receptor on ER; triggers Ca²⁺ release | | DAG | Membrane | Activates protein kinase C (PKC) | **High-Yield:** The IP₃/DAG pathway is distinct from the cAMP pathway—it does NOT involve adenylyl cyclase or phosphodiesterase. **Mnemonic:** **PLC = PIP₂ Lipase Cleaver** — remember PLC cuts PIP₂ into IP₃ and DAG. ### Why This Matters This is one of the two major intracellular signaling cascades tested in NEET PG. Defects in PLC signaling are implicated in cancer, metabolic disorders, and neurological disease.
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