The document discusses five classes of G protein-coupled receptors: A) Rhodopsin Family, the largest group which responds to neurotransmitters and neuropeptides; B) Secretin/glucagon receptor family which responds to peptide hormones; C) Glutamate receptor/calcium sensor family, a small group including GABAB and calcium sensing receptors; D) Frizzled G protein receptors; and E) Adhesion GPCRs. It also lists the main subtypes of G proteins - Gs, Gi, Go, and Gq - and their main effectors and clinical significance like stimulating or inhibiting adenylyl cyclase.

16. CLASS(sequence homology) RECEPTORS
A: Rhodopsin Family The largest group. Receptors for most amine
neurotransmitters, many neuropeptides,
purines etc.
B: Secretin/glucagon receptor family Receptor for Peptide hormones including
secretin, glucagon, calcitonin.
C: Glutamate receptor/calcium sensor family. Small group. GABAB receptor, Ca2+ sensing
receptors.
D:Frizzled G protein
E:Adhesion GPCR

20. Subtype Main effector Clinical significance
G ∞s Stimulates adenylyl
cyclase, causing increased
cAMP formation
Activated by cholera toxin
G ∞i Inhibits adenylyl cyclase,
decreasing cAMP
formation
Blocked by pertussis toxin
G ∞o Ca2+ inhibitor
G q Phospholipase C activation.