Which statement correctly describes DAG and IP3?

• A. DAG is hydrophobic and IP3 is hydrophilic
• B. IP3 is hydrophobic and DAG is hydrophilic
• C. Both are hydrophobic
• D. Both are hydrophilic

Answer: (A)

Understanding how the chemical nature of second messengers determines where they act helps explain this. Diacylglycerol (DAG) is a lipid with two fatty acid tails, which makes it hydrophobic and anchors it in the lipid bilayer of membranes. Inositol trisphosphate (IP3) is a highly polar molecule with three phosphate groups, making it hydrophilic and soluble in the cytosol, allowing it to diffuse to receptors such as the IP3 receptor on the endoplasmic reticulum. Therefore, DAG is hydrophobic and IP3 is hydrophilic. The other options conflict with their chemical structures, which explain why this statement is the correct description.