# Cell Receptors Cell receptors contain a *ligand binding domain (ED)* and an *effector domain (ED)*. ![[Pasted image 20250312035323.png|332]] --- > [!summary]+ Mechanistic Depiction of Ligand x Recepter Binding > > Inactive ($R$) and active ($R*$) conformations of the receptor are in equilbrium, which is described by the equilibrium constant $J$. > > ![[Pasted image 20250311010114.png|208]] > > Ligand ($L$) binding drives the receptor towards the active conformation ## Types of Ligands | Type | Description | | -------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | **Agonist** | Ligands which binds to a receptor and activates it. | | **Partial Agonist** | Ligands which bind to the receptor and activates it, but produces a smaller response.<br><br>(compared to a full agonist, even at full receptor occupancy) | | **Antagonists** | Ligands which bind to the receptor, but does NOT activate it.<br><br>It’s presence prevents agonists from binding and activating the receptor. | | **Inverse Agonists** | Ligands which bind to a receptor and reduces its basal (default) activity.<br><br>This is only relevant for receptors that have intrinsic activity even without a ligand. | ## Studying Cell Receptors Receptors can be isolated or expressed for experimentation - Purification of receptors can be performed using radiolabeled ligand. - Expression of receptor - Receptor types aren’t very abundant - Affinity purification - Expression of tagged receptor - Expression of receptor from a cloned gene - Functional expression assays - Western Blots