Some receptors are inside the cell
- The idea
- Predict
- See it
- Why
- Check
The idea
“Receptors sit in the plasma membrane, so every signal binds the outside of the cell.”
Most diagrams show receptors sticking out of the membrane. That's true for polar signals, but steroids pass straight through.
The short version
The mistake: Receptors sit in the plasma membrane, so every signal binds the outside of the cell.
What's actually true: Polar signals bind receptors on the surface. Small nonpolar signals, like steroids, cross the membrane and bind receptors inside.
- Small nonpolar steroids like cortisol, estrogen and testosterone dissolve through the membrane's nonpolar core. Charged or large polar signals, like insulin, can't.
- So polar signals, like insulin and epinephrine, bind receptors in the plasma membrane. Nonpolar ones can bind intracellular receptors in the cytosol or nucleus.
- There, the hormone and its receptor often act as a transcription factor. They bind DNA and change which genes are expressed.
On the exam: Ask if the signal can cross the membrane. If it can, like a steroid, its receptor can be inside.