What is the first step in the IP3 and DAG second-messenger system?

In the IP3 and DAG second-messenger system, the initial event involves the binding of the first messenger, which is typically a neurotransmitter or hormone, to a Gq protein-coupled receptor on the cell surface. This binding initiates a cascade of intracellular signaling events. Specifically, when the first messenger interacts with the Gq receptor, it causes a conformational change in the receptor that enables it to activate the associated Gq protein.

This activation is crucial because it leads to the subsequent activation of phospholipase C, the enzyme responsible for generating inositol trisphosphate (IP3) and diacylglycerol (DAG) from phosphatidylinositol 4,5-bisphosphate (PIP2) in the cell membrane. Therefore, identifying the first messenger binding event as the foundational step in the process lays the groundwork for all subsequent signaling that occurs within this second messenger pathway. This clear sequential understanding is essential for grasping how cellular signaling is mediated through G protein-coupled receptors.