Which component is ultimately responsible for calcium release from the endoplasmic reticulum in the phosphatidylinositol pathway?

Which component is ultimately responsible for calcium release from the endoplasmic reticulum in the phosphatidylinositol pathway?

• A. DAG
• B. IP3
• C. GTP
• D. Phospholipase C

Answer: (B)

In the phosphatidylinositol pathway, inositol trisphosphate (IP3) plays a critical role in mediating the release of calcium from the endoplasmic reticulum (ER). When a receptor on the cell surface is activated, it typically triggers the activation of phospholipase C, an enzyme that catalyzes the breakdown of a membrane lipid called phosphatidylinositol 4,5-bisphosphate (PIP2) into two secondary messengers: diacylglycerol (DAG) and IP3. Once formed, IP3 diffuses through the cytosol and binds to specific receptors on the membrane of the endoplasmic reticulum. This binding induces a conformational change in the IP3 receptor, leading to the opening of calcium channels. As a result, calcium ions stored in the ER are released into the cytosol, raising intracellular calcium levels and initiating various intracellular signaling pathways. DAG, while important in activating protein kinase C and facilitating various cellular responses, does not directly mediate calcium release from the ER. GTP is involved in G protein signaling, but it is not responsible for calcium release specifically in this pathway. Lastly, although phospholipase C is crucial

In the phosphatidylinositol pathway, inositol trisphosphate (IP3) plays a critical role in mediating the release of calcium from the endoplasmic reticulum (ER). When a receptor on the cell surface is activated, it typically triggers the activation of phospholipase C, an enzyme that catalyzes the breakdown of a membrane lipid called phosphatidylinositol 4,5-bisphosphate (PIP2) into two secondary messengers: diacylglycerol (DAG) and IP3.

Once formed, IP3 diffuses through the cytosol and binds to specific receptors on the membrane of the endoplasmic reticulum. This binding induces a conformational change in the IP3 receptor, leading to the opening of calcium channels. As a result, calcium ions stored in the ER are released into the cytosol, raising intracellular calcium levels and initiating various intracellular signaling pathways.

DAG, while important in activating protein kinase C and facilitating various cellular responses, does not directly mediate calcium release from the ER. GTP is involved in G protein signaling, but it is not responsible for calcium release specifically in this pathway. Lastly, although phospholipase C is crucial