Cannabis trichomes: How terpenes, cannabinoids and flavonoids are made

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Cannabis trichomes: How terpenes, cannabinoids and flavonoids are made

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Responsible for producing the protective, psychoactive, therapeutic and intoxicating properties of a cannabis plant, trichomes are the hairs found on the surface. Certain trichomes contain resin glands that create the terpenes, THCA, flavonoids, CBDA and other phytocannabinoids for which cannabis is known.

High accumulations of trichomes create the crystal-like sheen and stick feeling of cannabis buds. Trichomes are also found on the leaves and stems of the cannabis plant, although not all of these trichomes will be glandular, they’re most visible to the naked eye on the flowers. Non-glandular trichomes do help in maintaining the plant’s surface balance and add a layer of protection against adverse environmental conditions and pests, they do not produce the same psychoactive compounds as glandular trichomes.

Glandular trichomes produce terpenes, flavonoids and cannabinoids. There are three main types of glandular trichomes: bulbous, capitate-stalked and capitate-sessile. Cystoliths are what non-glandular trichomes are called.

Trichomes Picture
The glandular type of trichome produces cannabinoids, terpenes, and flavonoids.

The tiny bulbs that dot the surface of the cannabis plant are called bulbous trichomes. They require a microscope to be seen. They add a crystal-like sheen to the cannabis plant and add to the stickiness of the flower, although their production of cannabinoids is still in question. Bulbous trichomes are evenly distributed throughout the surface of the plant; they aren’t restricted to particular areas of cannabis.

Typically only visible with the aid of a microscope, capitate sessile trichomes are more abundant than bulbous trichomes. Capitate sessile trichomes have large bulbs like bulbous trichomes but with more of a classic mushroom-shaped structure. They’re primariliy found on the underside of the fan and sugar leaves.

Shaped like mushrooms containing a large bulb at the head of the stalk, capitate-stalked trichomes are the largest and most abundant trichomes in cannabis and can be seen with the naked eye. These are rarely seen on fan leaves, sugar leaves or stems but are primarily found on the surface of the cannabis flowers.

Types of Trichomes
Capitate-stalked trichomes are shaped like mushrooms and contain a large bulb at the head of the stalk.

How compounds are created in the cannabis trichome

In a process called biosynthesis, enzymes catalyze a series of chemical reactions to produce complex molecules from simple (smaller) ones, creating terpenes, flavonoids and cannabinoids within the trichome cells. Producing numerous psychotropic and therapeutic effects, phytocannabinoids, or cannabinoids produced by the cannabis plant interact with our body’s receptors. Supporting cannabinoids in producing desired effects are terpenes which are responsible for the aroma and flavours of cannabis. Offering their own unique therapeutic effects are flavonoids with are similar to terpenes in that they contribute to a cannabis plant’s aroma and flavour profile.

Binding, prenylation and cyclization are the three basic steps for cannabinoid biosynthesis. On a molecular level, the activity is as follows: Nanoscale macromolecules called enzymes bind to one or two small molecules (substrates), attach the substrates to each other (prenylation, catalytic chemical conversion of the substrates), then pass the small molecule (transformed substrate) down to another enzyme that processes it, making sequential changes to the small molecule (cyclization). Rather than using mechanical energy to build structures, enzymes are biological nanomachines that use chemical energy.

Some of the molecular structures involved in cannabinoid biosynthesis are depicted in the following figures. Each line is a bond between atoms in these figures. The atom is carbon by default when two lines meet at a point and no letter is written. Explicitly indicated are phosphorus and oxygen atoms. Hydrogen atoms are not drawn on the alkyl chains – only when bonded to oxygen or on the aromatic ring. There are some bonds that break and by-products that are formed which are not displayed, since not all steps are shown.

Produced themselves by a complex series of biosynthetic reactions, geranyl pyrophosphate and olivetolic acid are the precursors to all natural cannabinoids. With the assistance of an enzyme in the prenyltransferase category known as GOT, geranyl pyrophosphate and olivetolic acid bond to each other thus creating the first cannabinoid, CBGA (see Figure 1). Due to the presence of a carboxylic acid group in, CBGA, or cannabigerolic acid, an “A” is placed at the end of CBGA. It’s the same for the rest of the cannabinoids whose acronyms end with the letter A (THCA, CBDA, etc.). When heated, the carboxylic acid groups spontaneously break off the cannabinoid structures as carbon dioxide (CO2) gas, in a process called decarboxylation, after which the “A” designation is lost. Decarboxylated CBGA becomes CBG, as an example. Since it does not require enzymes and occurs after the plant is harvested, this is considered a degradation process.

Biosynthesis of CBGA
Figure 1: Biosynthesis of CBGA and decarboxylation to CBG. Note: All reaction steps are not shown and reactions are not balanced.

CBGA is the precursor to all other natural phytocannabinoids – It is also the first cannabinoid formed from a biosynthetic reaction that joined two smaller pieces together. Then, via the enzymes known as THCA synthase, CBDA synthase and CBCA synthase, CBGA is cyclized into THCA, CBDA or CBCA. Which cannabinoid is the major product from each particular strain and each particular cell is determined by the presence and relative quantities of the specific enzymes. The CBG type cannabinoids have only one ring in their structure. The THCA, CBDA and CBCA cannabinoids have more rings in their structures after the cyclization reactions (see Figure 2).

The creation of two new covalent bonds, a carbon-oxygen (C-O) bond and a carbon-carbon (C-C) bond, forms two new rings for THCA. One new C-C bond is created at the same position that the C-C bond formed in THCA, but without the new C-O bond by a reaction catalyzed in the CBDA synthase enzyme, thus forming CBDA. The formation of one (C-O) bond at a different position of the molecule than the (C-O) bond formed in THCA forms CBCA. Compounds with two rings fused to one another, such as in CBCA and CBC, are said to be bicyclic. That’s how THCA, CBDA, and CBCA are made through biosynthesis.

Cyclization of CBGA
Figure 2: Cyclization of CBGA into the three cannabinoids THCA, CBDA, and CBCA, followed by decarboxylation to produce THC, CBD, and CBC.

The most prominent cannabinoids will be the acidic forms of the cannabinoids (THCA, CBDA, CBCA, CBGA) when cannabis flower is dried and cured properly. These molecules decarboxylate when baked into edibles or smoked. The decarboxylation products are delta-9-THC, cannabidiol (CBD), and cannabichromene (CBC) (see Figure 2).

Cannabis’ effects are the result of complex developments of cannabinoids, terpenes and flavonoids that take place in the plant’s glandular trichomes.

This post is also available in: Français (French)

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