Biology / Unit 4 Bio 0777 short lesson, about 20 seconds
Cell-Surface Receptors: Three Domains
Captions available
The idea
A cell-surface receptor spans the membrane with an extracellular domain that binds ligand, a transmembrane domain, and an intracellular domain that passes the signal onward.
In practice
The extracellular domain binds ligand outside the cell, so the ligand never has to cross the membrane.
Where people slip
The receptor converts a signal at the membrane — the ligand's job ends at binding, not delivery inward.
Your place on the trail
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