Practice question

Cortical granules are dense membrane-bound vesicles arranged in monolayer underlying egg plasma membrane, stockpiled with proteases, peroxidase, glycosaminoglycans and structural proteins destined for rapid Ca2+-triggered exocytosis at fertilization. Detailed ultrastructural and biochemical comparison demonstrates striking homology with acrosomal vesicles of spermatozoa – both derive from Golgi apparatus in their respective gametes, contain hydrolytic enzymes, and undergo regulated SNARE-mediated exocytosis releasing contents to modify extracellular coats. Functionally, cortical reaction transforms vitelline layer similarly to how acrosomal reaction exposes bindin. They are not ribosomes, nuclei or lysosomes although enzymatically similar. Homology reflects shared evolutionary origin of secretory vesicles.