Practice question

Inositol 1,4,5-trisphosphate generated by phospholipase C diffuses through the cytosol and binds IP3-gated calcium channels on the endoplasmic reticulum. Channel opening releases stored Ca2+ into the cytosol, producing a rapid rise in free calcium that activates calmodulin-dependent enzymes and other calcium-sensitive effectors. The endoplasmic reticulum is therefore the primary source of IP3-mobilized calcium.