Practice question

Fertilization calcium signaling requires phospholipase C-gamma to generate second messenger IP3 that opens ER calcium channels. Upon Src tyrosine kinase activation at sperm entry site, PLC-gamma hydrolyzes PIP2 producing IP3 binding ER receptors releasing calcium globally as wave. If PLC-gamma inhibited pharmacologically with U73122 inhibitor, calcium wave fails and cortical granule exocytosis and activation do not occur. Direct microinjection of IP3 downstream restores calcium release even when PLC blocked, because IP3 directly opens ER channels bypassing lipid hydrolysis step. Calcium injection also triggers release but less faithfully. ATP and Bindin cannot substitute.