Question

Which of the following molecules is/are second messenger(s) produced by the phosphoinositide signaling cascade?

• A. Phosphatidylinositol 4,5-bisphosphate (PIP\(_2\))
• B. Diacylglycerol (DAG)
• C. Phosphatidylinositol 3,4,5-trisphosphate (PIP\(_3\))
• D. Inositol 1,4,5-trisphosphate (IP\(_3\))

Hint:

“PLC cuts PIP\(_2\) into two messengers”: \(\text{PIP}_2 \xrightarrow{\text{PLC}} \text{IP}_3 + \text{DAG}\). Think “IP\(_3\) = Ca\(^{2+}\) release; DAG = PKC activation.”

Answer 1

The Correct Option is B, D

Step 1: Core event. Activated PLC\(_\beta\) hydrolyzes membrane PIP\(_2\) to yield two second messengers: IP\(_3\) (cytosolic) and DAG (membrane-bound).
Step 2: Roles. IP\(_3\) triggers Ca\(^{2+}\) release from ER; DAG, together with Ca\(^{2+}\), activates PKC. PIP\(_2\) is the substrate/precursor, not itself a second messenger in this cascade. PIP\(_3\) belongs to the PI3K–Akt pathway, not the PLC–PIP\(_2\) cascade.