Summary
Seven-transmembrane receptors that activate G proteins to generate second messengers such as cAMP.
In depth
A ligand changes the receptor shape so it exchanges GDP for GTP on the associated G protein, which splits into alpha and beta-gamma subunits that act on effectors such as adenylyl cyclase or phospholipase C. GTP hydrolysis switches the signal off.
GPCRs are the largest receptor family and the target of about a third of drugs. They detect light, odours, hormones and neurotransmitters.
GPCRs have seven transmembrane helices and respond to hormones, neurotransmitters, light, odours and tastes; humans have around 800 of them. Rhodopsin in the retina is a GPCR, where light isomerises retinal and the G protein transducin activates phosphodiesterase, lowering cGMP and closing channels.
Desensitisation occurs when kinases phosphorylate the active receptor and arrestin binds, stopping G protein coupling and promoting internalisation, which explains why repeated drug doses often lose effect. Cholera toxin locks Gs in the active state, causing huge cAMP rises and loss of fluid, while pertussis toxin blocks Gi.
Example: beta-blockers block adrenaline binding to beta-adrenergic receptors, lowering heart rate and blood pressure.
Frequently asked questions
What is G Protein-Coupled Receptors?
Seven-transmembrane receptors that activate G proteins to generate second messengers such as cAMP.
Which area of biology covers G Protein-Coupled Receptors, and how advanced is it?
G Protein-Coupled Receptors is one of the 52 topics in Cell Biology. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Receptor Tyrosine Kinases, Second Messengers, Cell Signalling.
Can you give an example of G Protein-Coupled Receptors?
Rhodopsin in the retina is a GPCR; cholera toxin keeps a G protein permanently active, causing severe diarrhoea.
What should I learn before G Protein-Coupled Receptors?
Work through the Beginner topics in Cell Biology first, such as Cell Theory, Prokaryotic Cell, Eukaryotic Cell, then return to G Protein-Coupled Receptors. Advanced topics assume the Intermediate vocabulary.
What topics are related to G Protein-Coupled Receptors?
The closest topics to G Protein-Coupled Receptors are Receptor Tyrosine Kinases, Second Messengers, Cell Signalling, Cyclin-Dependent Kinases. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand G Protein-Coupled Receptors?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for G Protein-Coupled Receptors. To practise the whole of Cell Biology, use the Cell Biology quiz.
How is G Protein-Coupled Receptors different from Receptor Tyrosine Kinases?
G Protein-Coupled Receptors: Seven-transmembrane receptors that activate G proteins to generate second messengers such as cAMP. Receptor Tyrosine Kinases: Surface receptors that dimerise on ligand binding and autophosphorylate, triggering cascades like the Ras-MAPK pathway. Read both side by side and note what each one explains.
How should I study G Protein-Coupled Receptors step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Receptor Tyrosine Kinases and explain the difference aloud. Finally, take the Cell Biology quiz and come back to this page for any question you miss.