Practice question

Fertilization triggers awakening termed egg activation converting quiescent oocyte into metabolically active totipotent zygote preparing for mitosis. Central event is massive rise of intracellular free Ca2+ from endoplasmic reticulum after IP3 production by phospholipase C. Propagating calcium wave stimulates cortical granule exocytosis, cytoplasmic alkalinization via Na+/H+ antiporter, increased oxygen consumption, enhanced protein synthesis from maternal mRNAs, and cell cycle resumption through cyclin activation. Without Ca2+ elevation, shown by BAPTA chelation, none of these events occur, proving rise in intracellular Ca2+ drives activation and initiates embryogenesis.