Resetting a pathway doesn't take new proteins
- The idea
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The idea
“To switch a pathway off and ready it for the next signal, the cell has to destroy and remake its proteins.”
A switched-on protein can seem spent, like a struck match. Cells do remake proteins, just far too slowly to run a switch.
The short version
The mistake: To switch a pathway off and ready it for the next signal, the cell has to destroy and remake its proteins.
What's actually true: A pathway resets by undoing a change to the same proteins, like removing a phosphate. It's off in seconds and can fire again.
- A kinase adds a phosphate group to a protein, which changes its shape and activity. A phosphatase removes it, and the shape changes back.
- Phosphatases work the whole time. Activity stays high only while the signal keeps the kinases ahead. Once it's gone, activity falls, often within seconds.
- G proteins reset the same way. A G protein is on while it holds GTP and turns itself off by hydrolyzing it to GDP.
On the exam: A pathway turns off by undoing a change, so the same proteins can fire again.