More signal can't get past a broken step
- The idea
- Predict
- See it
- Why
- Check
The idea
“If one step in a pathway is broken, a strong enough signal will still get the message through.”
Turning a signal up sounds like it should push through anything. But a pathway is a relay, and a dropped handoff stops it however fast the first runner goes.
The short version
The mistake: If one step in a pathway is broken, a strong enough signal will still get the message through.
What's actually true: In a signaling chain, a broken step stops every step after it, so more signal can't restore the response.
- In a linear pathway, each protein switches on only the next one. A kinase does it by phosphorylation, adding a phosphate group to that protein.
- Steps upstream of a broken link, the ones before it, still run. Steps downstream, the ones after it, stay off.
- To restore the response, act at the broken step or after it. Supply what that step would have made, or an always-active later protein.
On the exam: Find the broken step. Only a fix at that step or after it can restore the response.