Norepinephrine acting on alpha-1 adrenergic receptors causes vascular smooth muscle contraction. Within this pathway, the membrane lipid fragment that remains anchored to the plasma membrane and directly activates protein kinase C is:
- A Inositol 1,4,5-trisphosphate
- B Diacylglycerol ✓
- C Phosphatidylinositol 4,5-bisphosphate
- D Cyclic AMP
Correct answer: B. Diacylglycerol
Explanation
Alpha-1 receptors are Gq coupled. Activated phospholipase C cleaves PIP2 into IP3, which releases calcium from the endoplasmic reticulum, and diacylglycerol, which stays embedded in the inner leaflet of the plasma membrane. Membrane-bound DAG plus rising cytosolic calcium activate protein kinase C, which phosphorylates targets leading to contraction. IP3 is water soluble and mobilizes calcium rather than activating PKC, so option A fails. Intact PIP2 is the substrate, not an activator.
Reference: Lippincott's Illustrated Reviews: Biochemistry, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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