A signal is only as fast as its steps
- The idea
- Predict
- See it
- Why
- Check
The idea
“Once a signal binds, the cell responds right away, whatever the pathway.”
Diagrams draw every signaling pathway as a few quick arrows. Some of those arrows take hours.
The short version
The mistake: Once a signal binds, the cell responds right away, whatever the pathway.
What's actually true: Each step after binding takes time. Channels act in milliseconds, cAMP in seconds to minutes, gene expression in minutes to hours.
- A ligand-gated ion channel is the receptor and the channel. Binding opens it, and ions change the membrane potential in milliseconds.
- A cAMP relay goes through a G protein, cAMP and kinases. It takes seconds to minutes, since it only switches on existing proteins.
- Changing gene expression means waiting for transcription and translation. That's minutes in bacteria and often hours in human cells.
On the exam: Count the steps after binding. A channel is fastest and new protein is slowest.