Explore the system
Three ways a receptor changes a cell
Compare a ligand-gated channel, a G protein-coupled receptor, and a growth-factor receptor.
Sources and model limits
Original schematic. Positions show relationships; structures and concentrations are not to scale.
- Julien's Primer of Drug Action · 15 · 3 · Three ways a receptor changes a cell · PDF 34, 35 · 3.2, 3.4, 3.5, 3.6
- Professor deck 3 · Trk / BDNF · PDF 15
Course notes and existing practice
What you will understand
Operate ionotropic and GPCR routes; classify mechanism without confusing it with location or effect.
Ionotropic receptors
In the nicotinic ACh example, ligand binding changes the receptor’s own channel gating. The ligand stays outside the pore and ions are distinct particles. NMDA’s extra activation conditions are not modeled by this simple channel.
G-protein-coupled receptors
The example GPCR binds ligand outside, activates a G protein inside and acts through an effector / second messenger on a separate channel. The intracellular signal is not the ligand. A missing connection blocks the downstream result. This is an illustrative route, not a claim that all GPCRs use the same messenger or open channels.
Classify the mechanism
Nicotinic ACh, AMPA, NMDA, kainate, GABA-A and 5-HT3 are ionotropic examples. Muscarinic ACh, dopamine receptors, adrenergic receptors, GABA-B and mGlu are GPCR examples. The 5-HT3 exception prevents a blanket classification of all serotonin receptors as metabotropic.
Trk receptors
The course includes Trk as a non-GPCR metabotropic category, including BDNF / TrkB. Do not force Trk into a G-protein chain.
Compare the dimensions
Location, mechanism, transmitter compatibility and auto/heteroreceptor role are separate dimensions. Presynaptic location alone does not identify an autoreceptor; the host neuron’s transmitter context matters. Excitatory/inhibitory effect is not a shortcut for mechanism.
Ionotropic receptor contains its channel. GPCR signals through G protein and effector to a separate channel. Boxes group related structures; positions are illustrative, not anatomical scale. Read the accompanying lesson for causal and alternative routes.
Adapted from the architecture digest and selected professor-deck pages inspected for this slice. Transcript wording remains digest-attributed. Diagrams are original and do not reproduce source images.
Adapted from the architecture digest and selected professor-deck pages inspected for this slice. Transcript wording remains digest-attributed. Diagrams are original and do not reproduce source images.
Julien connection: a distinction to explain on your own
Julien’s Chapter 3 examples should be read alongside the professor’s broader metabotropic classification: TrkB is a receptor tyrosine kinase, not a GPCR. Also keep affinity (binding), potency (concentration needed) and efficacy (attainable response) separate; a partial agonist need not be less potent.
Book connection: see the Julien Chapters 1–4 · Midterm study section in the Library for worked examples and recall practice. The cited source uses consolidated PDF page numbers.