Practice question

Slow block to polyspermy involves biochemical modification of zona pellucida called zona reaction. Cortical granules release ovastacin, an astacin-family metalloendoprotease that specifically cleaves ZP2 near its N-terminus, destroying N-terminal sperm-binding domain. Cleaved ZP2 no longer supports sperm adhesion, zona loses elasticity and hardens, preventing secondary sperm from penetrating or binding. This irreversible proteolysis, combined with glycosidase release and zinc crosslinking, provides durable post-fertilization barrier ensuring monospermic fertilization essential for diploid development, viability, normal embryogenesis, preventing triploid abortive conceptus formation and maintaining genomic integrity.