Drawing the Production of IP and DAG, and Their Role in Protein Phosphorylation
The correct answer and explanation is:
Correct Answer:
Diagram: Production of IP₃ and DAG and Their Role in Protein Phosphorylation
Signal (e.g., hormone, neurotransmitter)
↓
G Protein-Coupled Receptor (GPCR)
↓
Activation of Gq protein
↓
Activation of Phospholipase C-β (PLC-β)
↓
PIP₂ (Phosphatidylinositol 4,5-bisphosphate)
↓
Cleavage by PLC-β
/ \
IP₃ DAG
(Inositol (Diacylglycerol)
1,4,5-trisphosphate)
↓IP₃ ↓DAG
Binds to IP₃ Receptor Activates Protein Kinase C (PKC)
on Endoplasmic Reticulum
↓
Ca²⁺ Release into Cytosol
↓
Ca²⁺ + DAG together activate PKC
↓
**Protein Phosphorylation**
Explanation (300 words):
The production of inositol trisphosphate (IP₃) and diacylglycerol (DAG) is a critical pathway in cellular signal transduction that leads to protein phosphorylation. This signaling cascade typically begins when an extracellular signal, such as a hormone or neurotransmitter, binds to a G protein-coupled receptor (GPCR) on the cell membrane. This activates a specific subtype of G protein, known as Gq, which in turn activates the enzyme phospholipase C-β (PLC-β).
PLC-β acts on a membrane phospholipid called phosphatidylinositol 4,5-bisphosphate (PIP₂). It cleaves PIP₂ into two secondary messengers: inositol 1,4,5-trisphosphate (IP₃) and diacylglycerol (DAG).
IP₃ is water-soluble and diffuses through the cytoplasm to bind to IP₃ receptors on the endoplasmic reticulum (ER). This binding opens calcium channels, causing a release of Ca²⁺ ions into the cytosol. Elevated intracellular calcium concentration is vital for the activation of various proteins, including protein kinase C (PKC).
DAG, on the other hand, remains embedded in the plasma membrane and directly helps to activate PKC, but this activation is enhanced by the presence of calcium ions. Once activated, PKC phosphorylates specific target proteins, altering their activity, location, or interaction with other molecules.
This phosphorylation plays essential roles in numerous physiological processes, such as cell growth, metabolism, and gene expression. Thus, the IP₃-DAG pathway is a crucial link between external signals and internal cellular responses, especially via protein phosphorylation.