Final answer:
Peptide hormones initiate signaling cascades through cell-surface receptors. They activate a G-protein, which in turn activates an enzyme called phospholipase C-y (PLC-y). PLC-y hydrolyzes a molecule called phosphatidylinositol bisphosphate into second messengers: inositol trisphosphate (IP3) and diacylglycerol (DAG). These second messengers trigger specific cellular responses.
Step-by-step explanation:
Peptide hormones initiate signaling cascades through cell-surface receptors. When a peptide hormone binds to its receptor, it activates a G-protein, which in turn activates an enzyme called phospholipase C-y (PLC-y). PLC-y hydrolyzes a molecule called phosphatidylinositol bisphosphate into two second messengers: inositol trisphosphate (IP3) and diacylglycerol (DAG). IP3 is soluble in the cytosol and triggers the release of calcium ions, while DAG remains in the membrane and activates protein kinase C (PKC). These second messengers and the activated PKC then continue the signaling cascade, leading to specific cellular responses.