How much signal arrives changes the response
- The idea
- Predict
- See it
- Why
- Check
The idea
“If a signal reaches a cell, the cell gives its full response. If it doesn't, nothing happens.”
A single receptor is either bound or empty, so the whole cell seems to flip on or off. A cell has thousands of receptors, and how many are bound matters.
The short version
The mistake: If a signal reaches a cell, the cell gives its full response. If it doesn't, nothing happens.
What's actually true: Many responses depend on how much signal arrives. More signal can mean a stronger response, or a different one.
- A signal molecule, or ligand, binds its receptors. More ligand fills more receptors and sends a stronger message into the cell.
- So many responses are graded. A little signal gives a small response, and more gives a bigger one, until the cell reaches its maximum.
- Gene B needs more signal to switch on than gene A. Cells near the source turn on both, and cells farther out turn on only A. One signal can give cells different fates.
On the exam: Ask how much signal reaches the cell. The amount can set how strong the response is, or which one.