Practice question

Fertilization envelope does not arise de novo but represents transformed vitelline envelope. Before fertilization vitelline envelope tightly apposes egg plasma membrane and bears sperm receptors. Upon calcium-triggered cortical granule exocytosis, glycosaminoglycans released become highly hydrated osmotically drawing seawater into perivitelline space lifting envelope. Serine protease removes bound sperm and cleaves EBR1, hyalin creates inner supporting layer, ovoperoxidase catalyzes dityrosine crosslinks hardening envelope against mechanical penetration. This elevated modified structure is fertilization envelope, mechanically strong and biochemically non-adhesive, protecting embryo. Hyalin, glycosaminoglycans, or acrosomal proteins alone cannot form envelope without vitelline precursor.