Kinases add phosphates. Phosphatases remove them.
- The idea
- Predict
- See it
- Why
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The idea
“A phosphatase adds the phosphate, so blocking it switches a pathway off.”
Only the phosphatase has "phosphate" in its name, so it's easy to assume it adds one. It actually takes it off.
The short version
The mistake: A phosphatase adds the phosphate, so blocking it switches a pathway off.
What's actually true: A kinase uses ATP to add a phosphate to a protein. A phosphatase removes it. Blocking a phosphatase keeps the phosphate on.
- A kinase moves a phosphate group from ATP onto a protein. That's phosphorylation. The phosphate changes the protein's shape, often switching it on and sometimes off.
- A phosphatase removes the phosphate and returns the protein to its starting shape. That's dephosphorylation, and it uses no ATP.
- In a signaling cascade, each kinase phosphorylates the next protein. Block one and the signal stops. Phosphatases undo this, so the response fades when the signal ends.
On the exam: Kinase puts the phosphate on. Phosphatase takes it off. Block the phosphatase and the response stays on.