Practice question

Acrosomal reaction is exocytotic fusion of sperm plasma membrane with outer acrosomal membrane releasing enzymatic cargo after binding zona pellucida. Key event is secretion of serine protease acrosin, hyaluronidase and esterases that locally hydrolyze ZP glycoprotein filaments, particularly ZP2 and ZP3, creating penetration tract. Calcium influx mediated via ZP3-triggered signaling and CatSper amplifies fusion. Repulsive interaction or simple plasma membrane fusion does not describe enzymatic step; fusion of gamete membranes occurs later in perivitelline space after zona traversal. Thus reaction functionally corresponds to zona digestion enabling sperm transit to egg surface for subsequent Izumo-Juno mediated fusion.