The second messenger DAG directly _.
Multiple Choice:
activates PLC
causes a rise in cytosolic Ca2+ concentration
activates IP3
activates PKC
activates a plasma membrane Ca2+ ATPase
The Correct Answer and Explanation is :
The correct answer is: activates PKC.
Explanation:
DAG (diacylglycerol) is a second messenger that plays a crucial role in signal transduction pathways, especially in the activation of protein kinase C (PKC). This process begins when a receptor on the cell surface is activated by a ligand (such as a hormone or neurotransmitter). This activation triggers a signaling cascade involving the enzyme phospholipase C (PLC).
Here’s how it works:
- Activation of PLC: Upon ligand binding, PLC is activated and hydrolyzes a phospholipid called phosphatidylinositol 4,5-bisphosphate (PIP2) found in the plasma membrane. This cleavage results in the formation of two important second messengers: inositol trisphosphate (IP3) and diacylglycerol (DAG).
- Role of DAG: DAG remains embedded in the plasma membrane. It does not directly activate PLC but rather has an important role in activating protein kinase C (PKC). When DAG is produced, it binds to and activates PKC, a family of enzymes that regulate various cellular processes like cell growth, differentiation, and apoptosis.
- PKC Activation: PKC is a serine/threonine kinase, and its activation by DAG leads to its translocation from the cytosol to the plasma membrane. Once there, PKC is activated by DAG and can phosphorylate specific target proteins involved in cellular responses.
- Ca2+ and IP3: IP3, another product of PIP2 hydrolysis, is involved in releasing calcium ions (Ca2+) from intracellular stores, which increases the cytosolic concentration of Ca2+. However, DAG itself does not directly cause this rise in Ca2+; rather, it primarily works through PKC activation.
Thus, DAG plays a pivotal role in activating PKC, which then initiates downstream signaling cascades that mediate cellular responses to the original signal.