Question

What are the two intracellular messengers that are obtained by hydrolysis of phosphatidylinositol bisphosphate?
A. Monoacylglycerol
B Diacylglycerol
C. Triacylglycerol
D. Inositol 1,4,5 trisphosphate
Choose the correct answer from the options given below:

• A. A and D only
• B. B and D only
• C. C and D only
• D. A and B only

Hint:

To remember this pathway: \(\text{PIP}_2 \xrightarrow{\text{PLC}} \text{IP}_3 \text{ (cytosolic, releases } \text{Ca}^{2+}\text{)} + \text{DAG (membrane-bound, activates PKC)}\).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Signal transduction pathways utilize cell membrane phospholipids to amplify extracellular signals.
A key pathway involves the hydrolysis of the membrane lipid phosphatidylinositol 4,5-bisphosphate (\(\text{PIP}_2\)) to generate secondary messengers.

Step 2: Detailed Explanation:
When an extracellular agonist binds to G-protein-coupled receptors associated with the \(\text{G}_q\) protein, it activates the enzyme Phospholipase C (PLC).
PLC catalyzes the cleavage of the ester bond in the phospholipid \(\text{PIP}_2\), yielding two secondary messengers:
Inositol 1,4,5-trisphosphate (\(\text{IP}_3\) Statement D): A soluble, polar molecule that diffuses through the cytosol to bind to \(\text{IP}_3\)-gated calcium channels on the membrane of the endoplasmic reticulum. This triggers the release of stored calcium ions (\(\text{Ca}^{2+}\)) into the cytosol.
Diacylglycerol (DAG Statement B): A hydrophobic molecule that remains embedded in the plasma membrane. It recruits and, in concert with calcium ions, activates Protein Kinase C (PKC), which phosphorylates target proteins to regulate cellular responses.
Thus, the correct messengers are Diacylglycerol (B) and Inositol 1,4,5-trisphosphate (D).

Step 3: Final Answer:
The two intracellular messengers obtained by the hydrolysis of \(\text{PIP}_2\) are Diacylglycerol and Inositol 1,4,5-trisphosphate (B and D only).