Final answer:
Phosphatidylinositol bisphosphate (IP3) is derived from a phospholipid, resulting from the action of phospholipase C on PIP2. IP3 acts as a second messenger in the cell, participating in a signaling cascade by releasing Ca²⁺ from the endoplasmic reticulum.
Step-by-step explanation:
Phosphatidylinositol bisphosphate (IP3) is a second messenger molecule derived from a phospholipid. The enzyme phospholipase C cleaves a specific phospholipid, phosphatidylinositol 4,5-bisphosphate (PIP2), to form two molecules that serve as second messengers: diacylglycerol (DAG) and inositol triphosphate (IP3).
Diacylglycerol (DAG) remains in the plasma membrane and activates protein kinase C (PKC), which phosphorylates target proteins. Conversely, IP3 diffuses into the cytoplasm and binds to ligand-gated calcium channels on the endoplasmic reticulum, triggering the release of Ca²⁺ ions that further propagate the signal cascade. This pathway can be activated by various stimuli, including hormone binding to cell surface receptors, which then interacts with G-proteins leading to phospholipase C activation.