Practice question

Egg activation involves resumption of meiosis, elevation of metabolism, and preparation for embryonic cleavage. Central event is single propagated calcium wave sweeping from sperm entry point throughout cytoplasm, raising cytosolic calcium over tenfold. Calcium activates calmodulin-dependent kinase II leading to cyclin B degradation and release from M-phase arrest, stimulates NAD kinase increasing NADPH, triggers cortical granule fusion, and opens Na+/H+ exchangers raising pH to promote protein synthesis. ATP increase, pH rise, and sperm nuclear incorporation are downstream consequences of calcium signaling. Without calcium transient, eggs remain arrested even if sperm fuses, proving calcium rise as primary activator.