Final answer:
1,2-diacylglycerol (DAG) activates protein kinase C and facilitates the release of calcium from the endoplasmic reticulum, playing a critical role in cell signaling by modifying protein activities and participating in signal transduction cascades.
Step-by-step explanation:
1,2-diacylglycerol (DAG) is a molecule that plays an essential role in cell signaling pathways. It is a product of phosphatidylinositol bisphosphate (PIP₂) cleavage by the enzyme phospholipase C. Upon formation, DAG remains within the plasma membrane, where it performs two main functions. Firstly, it binds to and activates protein kinase C (PKC), which is involved in the phosphorylation of serine and threonine residues on numerous proteins, thereby altering their activities. Secondly, DAG cooperates with inositol triphosphate (IP3) to enhance calcium release from the endoplasmic reticulum, contributing to the signal transduction cascades initiated by various hormones and other stimuli.