During signal transduction, one molecule of phosphatidylinositol 4,5-bisphosphate (PIP2) is
cleaved into one molecule each of inositol triphosphate (IP3) and diacylglycerol (DAG) by the
enzyme:
A. Lipolyase C,
B. Phosphatase C,
C. Phosphodiesterase C,
D. Phospholipase C,

Signal Transduction and the Role of Phospholipase C

Introduction

Cell signaling is an intricate process that allows cells to respond to external stimuli. One of the critical steps in this process is the cleavage of phosphatidylinositol 4,5-bisphosphate (PIP2), a membrane phospholipid, into two powerful second messengers—inositol triphosphate (IP3) and diacylglycerol (DAG). But which enzyme is responsible for this cleavage? Let’s explore the mechanism and identify the key player.

The Key Enzyme: Phospholipase C

The correct answer to this biochemical puzzle is:

Option D: Phospholipase C

Phospholipase C (PLC) is an enzyme that specifically hydrolyzes PIP2 into IP3 and DAG.

How the Reaction Works

1. Activation: When a signaling molecule (like a hormone or neurotransmitter) binds to a G protein-coupled receptor (GPCR) or receptor tyrosine kinase (RTK), it activates phospholipase C.
2. Cleavage of PIP2: PLC then cleaves PIP2, a phospholipid located on the inner leaflet of the plasma membrane.
3. Formation of Second Messengers:
   • IP3 is released into the cytosol where it binds to receptors on the endoplasmic reticulum, triggering the release of Ca2+ ions.
   • DAG remains in the membrane and activates protein kinase C (PKC), a key player in various signaling cascades.

Importance in Cellular Function

The IP3-DAG pathway regulates many vital functions such as:

• Cell growth and differentiation
• Metabolism
• Immune responses
• Neural signaling

Any disruption in this pathway can lead to diseases, including cancers and neurological disorders.

Conclusion

Phospholipase C plays a central role in the signal transduction pathway by cleaving PIP2 into IP3 and DAG. This event initiates a cascade of intracellular reactions that control numerous physiological processes.

So, if you’re prepping for an exam or simply expanding your cell biology knowledge, remember:

Phospholipase C is the enzyme that cleaves PIP2 into IP3 and DAG.

Key Phrase:

Phospholipase C cleaves PIP2 into IP3 and DAG