Cell Receptors and Signaling Quiz

Internal and Intracellular Receptors

• Found in the cytoplasm and respond to hydrophobic ligand molecules.
• Hydrophobic signaling molecules typically diffuse across the plasma membrane.
• Interact with intracellular receptors located in the cytoplasm.

Cell-Surface/Transmembrane Receptors

• Involved in signal transduction, converting extracellular signals to intracellular responses.
• Composed of three main components:
  • External ligand-binding domain (extracellular).
  • Hydrophobic membrane-spanning region.
  • Intracellular domain.

Types of Cell-Surface Receptors

• Three general categories:
  • Ion channel-linked receptors.
  • G-protein-linked receptors.
  • Enzyme-linked receptors.

Ion Channel-Linked Receptors

• Bind with ligands (e.g., Nicotinic receptor).
• Open channels to allow specific ions (Na, Ca, Mg, H2) to pass through due to conformational changes.

Enzyme-Linked Receptors

• Cell surface receptors associated with enzymes; feature large extracellular and intracellular domains.
• Ligand binding activates the enzyme and triggers cellular responses (e.g., Tyrosine Kinase receptor).

G-Protein Linked Receptors

• Activate a membrane protein called G-protein upon ligand binding.
• Specific to each receptor with dedicated extracellular domains and G-protein binding sites.
• Example: Beta-adrenergic receptor.

Types of G-Protein Receptors

• Gs receptor: Activates adenylyl cyclase to produce cAMP.
• Gi receptor: Inhibits adenylyl cyclase, reducing cAMP levels.
• Gq receptor: Activates phospholipase C (PLC), producing secondary messengers DAG and IP3.

Secondary Messengers

• cAMP: A cyclic nucleotide involved in signaling pathways.
• DAG (Diacylglycerol): Activates protein kinases and elicits diverse responses.
• IP3 (Inositol triphosphate): Triggers intracellular calcium release and various cellular effects.

Forces Affecting Ligand-Receptor Binding

• Three major types of chemical bonds:
  • Covalent bonds: Strong and stable, often irreversible (e.g., Phenoxybenzamine with alpha-adrenergic receptor).
  • Electrostatic bonds: Weaker, with variable interaction strength (e.g., Van-der Waals forces).
  • Hydrophobic interactions: Generally weak but crucial for biological membrane interactions.

Ligand-Receptor Interactions

• Two primary types: agonism and antagonism.

Agonists

• Three types:
  • Full agonist: Fully activates the effector system with high receptor affinity.
  • Partial agonist: Produces less than full effect; can act as an antagonist in the presence of a full agonist (e.g., Morphine + Naloxone).
  • Inverse agonist: Stabilizes inactive receptor conformation, producing effects opposite to full agonists (e.g., GABA receptors).

Antagonists

• Five types:
  • Competitive antagonist: Binds reversibly without activating the receptor, shifting response curve to the right (e.g., Propranolol and Isoproterenol).
  • Non-competitive antagonist: Causes downward shift in response curve, not overcome by more agonist (e.g., Phenoxybenzamine).
  • Physiological antagonist: Binds to different receptors, producing opposite effects (e.g., Histamine and Epinephrine).
  • Chemical antagonist: Directly interacts with the drug being antagonized, preventing it from reaching the target (e.g., Dimercaprol for lead poisoning).
  • Allosteric antagonist: Binds to a site other than the active site and modifies receptor function.

Conclusion

• Understanding receptor types, signaling mechanisms, and interactions is critical for pharmacology and therapeutic applications.

Test your knowledge on the various types of cell receptors and their functions in signaling processes. The quiz covers internal and intracellular receptors, as well as cell-surface receptors, including their components and types. Dive deep into the mechanisms of how these receptors interact with ligands and transduce signals.