A signal's range comes from how fast it is removed
- The idea
- Predict
- See it
- Why
- Check
The idea
“How far a signal reaches depends on how much the cell releases, how big it is, or how it binds its receptor.”
A louder voice carries farther, so it seems more signal should reach much farther too. Signal molecules just drift until something catches or cuts them.
The short version
The mistake: How far a signal reaches depends on how much the cell releases, how big it is, or how it binds its receptor.
What's actually true: How far a local signal reaches depends on how fast it is trapped or broken down on the way.
- In paracrine signaling, a cell releases a signal into the fluid between cells. The signal diffuses outward until something removes it.
- Enzymes can break it down. The extracellular matrix, the mesh of proteins around cells, can trap it. Cells can take it in. Faster removal means a shorter range.
- Releasing more raises the level everywhere, but the signal still fades at the same rate. Removal is what makes it fade, so removal is what keeps it local.
- Receptors decide which cells respond. They shorten the range only when they capture the signal and pull it out of the fluid.
On the exam: Ask what removes the signal on the way. Faster removal means a shorter reach.