The lipid composition of the two monolayers of the plasma membrane is quite different. This lipid asymmetry is functionally relevant, especially in converting extracellular signals into intracellular ones. Given below are a few membrane lipids:

A. Phosphatidylserine
B. Phosphatidylinositol 4-phosphate
C. Phosphatidylcholine
D. Sphingomyelin

Choose the option that correctly defines all the lipids involved in signaling and are restricted to the cytosolic face of the plasma membrane.

Correct option is B

The correct option is (b)

EXPLANATION-

​The plasma membrane consists of two layers (monolayers) of lipids, each having a distinct composition. This asymmetry is crucial for various functions, including cell signaling, membrane curvature, and recognition.
     The outer leaflet (facing the extracellular space) mainly contains phosphatidylcholine (PC) and sphingomyelin (SM).
     The inner leaflet (facing the cytosol) mainly contains phosphatidylserine (PS), phosphatidylinositol phosphates (like phosphatidylinositol 4-phosphate, PIP), and other signaling lipids.

A   Phosphatidylserine (PS):
PS is negatively charged and localized primarily in the inner leaflet. It plays key roles in signaling pathways and membrane dynamics.

B   Phosphatidylinositol 4-phosphate (PIP):
PIPs are phosphorylated derivatives of phosphatidylinositol, essential for cell signaling. They are found on the cytosolic side where they serve as precursors for other signaling molecules.

C   Phosphatidylcholine (PC):
PC is mostly in the outer leaflet and generally not directly involved in intracellular signaling.

D   Sphingomyelin (SM):
SM is mainly found on the outer leaflet and is more structural than signaling-focused.

Lipids restricted to the cytosolic face and involved in signaling are:
        A    Phosphatidylserine (A)
        B    Phosphatidylinositol 4-phosphate (B)
Hence, Option 2: A and B is the correct choice.