Transmembrane proteins. Illustration of five transmembrane proteins with their ligands (left to right): a potassium channel, a delta-opioid receptor, an LDL (low-density lipoprotein) receptor, an acetylcholine receptor, and a histamine receptor. Each channel or receptor is shown with its associated ligands: a potassium ion (purple sphere), an endorphin molecule , an LDL droplet (spherical lipid particle), an acetylcholine molecule, and a histamine molecule. They are all shown embedded in the lipid bilayer of the cell membrane (orange and blue). |