Thinking GTP and phosphates power the next step
- The idea
- Predict
- See it
- Why
- Check
The idea
“Adding a phosphate or GTP gives a protein energy, and that energy powers the next step.”
You learned ATP as the cell's energy molecule. Phosphates come from ATP, and GTP and cAMP look a lot like it, so they seem like fuel too.
The short version
The mistake: Adding a phosphate or GTP gives a protein energy, and that energy powers the next step.
What's actually true: A phosphate, GTP or cAMP changes a protein's shape, which turns it on or off. None of them is spent as fuel.
- A phosphate adds negative charge to a protein, which changes its shape and turns it on or off. Kinases add phosphates, taking each one from ATP. Phosphatases remove them.
- GTP and cAMP are switches too. A G protein is on while it holds GTP and turns off when it breaks GTP to GDP. cAMP binds protein kinase A to turn it on.
On the exam: In signaling, a phosphate, GTP or cAMP is a switch. Ask what turns it on and what turns it off.