Many signals work without entering the cell
- The idea
- Predict
- See it
- Why
- Check
The idea
“A signal has to get inside the cell to change anything.”
A signal changes what happens inside a cell, so it's easy to picture it getting in. Many never do.
The short version
The mistake: A signal has to get inside the cell to change anything.
What's actually true: Polar or large signals stay outside and bind surface receptors, while small nonpolar ones like steroids cross the membrane.
- The lipid bilayer decides which signals can get in. Small nonpolar ones like steroid hormones pass through. Polar or large ones like insulin can't.
- Those bind a receptor protein that spans the membrane. Binding changes the receptor's shape, which starts signal transduction, a relay inside the cell.
- The relay can reach the nucleus and turn genes on. A signal that stays outside can still change gene expression.
On the exam: Ask if it can cross the bilayer. Small and nonpolar goes in. Polar or large binds a surface receptor.