Practice question

At sea urchin fertilization, sperm-egg fusion activates Src family tyrosine kinases that phosphorylate and activate phospholipase C-gamma. PLC-gamma hydrolyzes phosphatidylinositol bisphosphate PIP2 in plasma membrane into diacylglycerol DAG and inositol trisphosphate IP3. IP3 diffuses to endoplasmic reticulum binding IP3 receptors, opening calcium channels and initiating calcium wave from internal stores propagating across egg. This IP3-triggered calcium release drives cortical granule exocytosis, elevation of fertilization envelope, and resumption of meiosis. Zona glycoproteins and protamines do not directly trigger intracellular calcium release.