Final answer:
In the calmodulin activation pathway, the inositol phospholipid is phosphatidylinositol (PI), which is phosphorylated to form PIP and PIP₂. PIP₂ is cleaved by phospholipase C to produce DAG and IP3.
Step-by-step explanation:
In the calmodulin activation pathway, the inositol phospholipid that plays a key role is known as phosphatidylinositol (PI).
Enzymes called kinases phosphorylate PI to form PI-phosphate (PIP) and PI-bisphosphate (PIP₂), which are involved in cellular signaling. PIP₂ is then cleaved by the enzyme phospholipase C to produce two second messengers: diacylglycerol (DAG) and inositol triphosphate (IP3).
DAG remains in the plasma membrane and activates protein kinase C, while IP3 diffuses into the cytoplasm and binds to ligand-gated calcium channels in the endoplasmic reticulum to release Ca²+ and continue the signal cascade.