Practice question

Acrosomal reaction is calcium-dependent exocytosis of acrosomal vesicle at anterior sperm head occurring after zona pellucida binding. Fusion of outer acrosomal membrane with plasma membrane releases soluble enzymes including acrosin, hyaluronidase and other proteases. These lysins locally digest zona pellucida glycoprotein matrix, creating penetration slit allowing sperm to reach perivitelline space. Reaction also exposes inner acrosomal membrane proteins like Izumo1 essential for egg fusion. Without zona digestion sperm cannot traverse thick extracellular coat, making this enzymatic breaching crucial for successful fertilization in mammals.