4.2 Introduction to Signal Transduction

Three stages of signaling

A signal is handled in three steps: reception (the signal molecule, or ligand, binds a receptor), transduction (the signal is relayed and converted through the cell), and response (the cell changes its activity).

Where receptors are

Membrane receptors sit in the plasma membrane and detect large or polar ligands that can't enter the cell. Intracellular receptors are inside the cell and detect small, nonpolar ligands like steroid hormones, which can cross the membrane.

Key terms

Reception

Stage 1: the signal molecule (ligand) binds its receptor.

Transduction

Stage 2: the signal is relayed and converted through the cell.

Response

Stage 3: the cell changes its activity in reaction to the signal.

Ligand

The signaling molecule that binds and activates a receptor.

Membrane vs. intracellular receptor

Membrane receptors detect large/polar ligands; intracellular receptors detect small nonpolar ones.

Try an AP-style question

What are the three stages of cell signaling, in order?

1. Reception, transduction, response
2. Response, reception, transduction
3. Transduction, reception, response
4. Reception, response, transduction