Final answer:
DAG and IP3 originate from the cell membrane, through the action of phospholipase C on PIP2, with IP3 affecting the endoplasmic reticulum.
Step-by-step explanation:
DAG (Diacylglycerol) and IP3 (Inositol trisphosphate) are both molecules that play a role in the signaling pathways inside cells. These molecules originate from the cell membrane. Specifically, they are the result of the hydrolysis of PIP2 (phosphatidylinositol 4,5-bisphosphate) by the enzyme phospholipase C into DAG and IP3. DAG remains in the membrane and acts there, while IP3 is released into the cytoplasm, where it binds to receptors on the endoplasmic reticulum, leading to the release of calcium ions into the cytosol and further propagation of the signal.