A phosphate switches the next kinase on
- The idea
- Predict
- See it
- Why
- Check
The idea
“When a kinase adds a phosphate to a protein, it shuts that protein off.”
Kinases and phosphatases come as a matched pair, so it's easy to swap which one is the on switch.
The short version
The mistake: When a kinase adds a phosphate to a protein, it shuts that protein off.
What's actually true: In a kinase cascade, a phosphate switches each relay protein on. A phosphatase switches it off by taking the phosphate away.
- A kinase moves a phosphate from ATP onto another protein. That's phosphorylation.
- The phosphate's negative charge changes the protein's shape. In a cascade, that new shape is the active one.
- A phosphatase removes the phosphate, and the protein goes back to its inactive shape. That's how the cascade shuts down.
On the exam: A kinase's phosphate turns a relay protein on. A phosphatase turns it off by taking the phosphate away.