Not every second messenger acts like cAMP
- The idea
- Predict
- See it
- Why
- Check
The idea
“Every second messenger is like cAMP. An enzyme makes it, it floats in the cytosol, and it turns on a kinase.”
cAMP is usually the first second messenger you learn, so it becomes the model for the rest. The others break some of its rules.
The short version
The mistake: Every second messenger is like cAMP. An enzyme makes it, it floats in the cytosol, and it turns on a kinase.
What's actually true: DAG stays in the membrane, IP3 opens Ca2+ channels, and Ca2+ is moved into the cytosol, never made.
- A messenger that dissolves in water, like IP3, can move through the cytosol. DAG is a lipid, so it stays in the membrane.
- IP3 opens Ca2+ channels in the ER instead of binding a kinase. Cells can't make Ca2+, so they store it and release it on signal.
- Protein kinase C needs both DAG and Ca2+ to switch on. So the two pieces of the cut lipid work together.
On the exam: Ask of each messenger whether it is made or released, where it can go, and what it binds.