CBGA, cannabigerolic acid, is the branch point of cannabinoid biosynthesis. A prenyltransferase enzyme attaches a ten-carbon geranyl group (from geranyl pyrophosphate) to olivetolic acid, producing CBGA in the trichome head. Three oxidocyclase enzymes then compete for it: THCA synthase makes THCA, CBDA synthase makes CBDA and CBCA synthase makes CBCA. Whatever isn't converted stays as CBGA.
In practice
That competition is why the THC:CBD ratio is mostly a genetic trait. A plant's synthase alleles decide where the CBGA goes. Growers sometimes call CBGA the "mother cannabinoid", a convenient image but chemically it is simply the shared precursor. Decarboxylation turns any remaining CBGA into CBG.
Don't confuse with
- CBG: the neutral form, after decarboxylation.
- Olivetolic acid: one of CBGA's two building blocks, not a cannabinoid itself.
- CBGVA: the propyl (C3) analogue, made from divarinic acid, which leads to THCVA and CBDVA.
A cannabinoid is any compound that binds the body's cannabinoid receptors or shares the typical cannabis terpenophenolic structure; the plant-made ones are phytocannabinoids such as THCA and CBDA.Trichome heads are the bulbous resin-filled tops of capitate glandular trichomes, where cannabis makes and stores nearly all its cannabinoids and terpenes; they are the raw material of hash.THCA synthase is the trichome enzyme that converts CBGA into THCA; which alleles of its gene a plant carries largely decides whether it is THC-dominant.THCA (tetrahydrocannabinolic acid) is the acid cannabinoid that drug-type cannabis makes in its trichomes; heat or time decarboxylates it into THC, losing about 12% of its mass.CBDA synthase is the trichome enzyme that converts CBGA into CBDA; it competes with THCA synthase, and its alleles largely decide whether a plant is CBD-dominant.The chemotype ratio is the balance of a plant's main cannabinoids, usually THC to CBD, classing plants as type I (THC-dominant), II (mixed), III (CBD-dominant), IV (CBG) or V (near-zero).Decarboxylation is the loss of a carboxyl group as CO2 that turns acid cannabinoids such as THCA and CBDA into neutral THC and CBD, quickly with heat, slowly with time.CBG (cannabigerol) is the neutral, decarboxylated form of CBGA, the cannabinoid precursor; most plants convert nearly all of it onward, but some cultivars are bred to accumulate it.Olivetolic acid is the phenolic building block of cannabinoids; joined to geranyl pyrophosphate it forms CBGA, and its five-carbon chain becomes the pentyl tail of THC and CBD.Geranyl pyrophosphate (GPP) is a ten-carbon terpene precursor that cannabis uses both to build monoterpenes and, joined to olivetolic acid, to make the cannabinoid precursor CBGA.
