WAXES (BIOLOGICAL): STRUCTURE, PROPERTIES, FUNCTION, TYPES - BIOLOGY - 2025

A wax is a hydrophobic material made up of long-chain fatty acids and alcohols (esters of long-chain fatty acids and alcohols). They have multiple functions in nature, as they are produced naturally by many plant and animal species.

The word “wax” (from English wax) derives from the Latin word “wax”, which refers to the substance produced by bees and used to build their combs. The term in English is used with the same connotation, as it derives from the Anglo-Saxon word “weax” also used to describe beeswax (in English beeswax).

A honeycomb (Image by Pexels at www.pixabay.com)

Taking into account the above, then it is understood that the definition of "wax" encompasses a set of substances that share some characteristics but do not necessarily have the same chemical and / or physical properties.

However, regardless of their chemical identity, waxes are highly hydrophobic substances that serve different purposes depending on the organism that produces them. A large number of living beings use them as the main energy reserve substance, while others use them as protective substances on their surface.

Although they are just as common in plants and animals, plant waxes are the ones that have been described with the greatest intensity (and some of certain animals), since they have biological importance for these organisms and also industrial from the anthropological point of view.

Structure of waxes

Waxes have been classically defined as alcoholic esters of long chain fatty acids, characterized by lengths of 24-30 carbon atoms, which associate with primary alcohols of 16-36 carbon atoms (likewise, they can associate with alcohols from steroid group).

They are formed by reactions that involve the "union" of an alcohol and a fatty acid, more or less as follows:

CH3 (CH2) nCH2OH (alcohol) + CH3 (CH2) nCOOH (fatty acid) → CH3 (CH2) nCH2COOHCH2 (CH2) CH3 (wax ester) + H2O (water)

The nature of the aliphatic components of waxes can be enormously variable, and can be found in these fatty acids, primary and secondary alcohols, hydrocarbons, sterol esters, aliphatic aldehydes, ketones, diketones, triacylglycerols, triterpenes and sterols, among others.

In the same way, both the chain length and the degree of saturation and branching of the fatty acids and the other aliphatic components of the waxes depend on their origin.

Knowing this, it has been shown that those waxes produced in plants are different and those that are produced by marine animals and by terrestrial animals, for example.

Wax properties

Waxes have different physicochemical properties that can be summarized in a small list:

- Its texture can vary from soft and manageable to hard (plastic) or "breakable" at 20 ° C

- They are generally very low viscosity

- They are highly insoluble in water, but they are in organic solvents, although this process depends a lot on temperature

Function

Waxes fulfill multiple functions both in the animal kingdom and in the vegetable kingdom, as they are extremely common substances in nature.

In animals

Waxes represent the main energy storage compound for the floating microorganisms that make up plankton.

Thus, waxes are at the same time one of the main metabolic sources at the base of the food chain of marine animals.

Animals have special dermal glands that secrete wax in order to protect their skin and hair, making them more flexible, lubricated and water-repellent structures.

Birds have a gland known as the “uropygeal” gland, which constantly secretes waxes, which is why it is responsible for keeping the feathers “waterproof”.

In plants

A primary function of waxes in plant organisms is the protection of tissues.

A good example of this is the waxy coating on the leaf blades of many plants, which reduces heat dehydration induced by sunlight.

Another example that can be mentioned is the waxy coating that many seeds have in their coat, which helps them avoid water loss during storage.

These waxes are usually embedded between cutin and suberin polymers, constituting an amorphous layer on the outer surface of the plant. Many plants have an epicuticular layer of waxy crystals that overlap the cuticle and give them a grayish or glaucous appearance.

Waxes not only prevent water loss, but can also help the plant to prevent some fungal or bacterial pathogens, and play a fundamental role in plant-insect interactions, in addition to preventing damage caused by ultraviolet radiation.

In the industry

Waxes of biological origin are also very useful from an industrial point of view, as they are used in the production of drugs, cosmetics, etc.

The lotions typically used to hydrate the skin, as well as polishes and some ointments, are made up of fat mixtures with beeswax, Brazilian palm wax, lambswool wax, sperm whale wax, etc.

Waxes are also widely used in industrial coatings that allow water repellency, as well as in the manufacture of substances used to polish automobiles.

They are used in the plasticizing of hot melts, in the lubrication of work equipment in the metallurgical industry and to allow the delayed release of compounds used in agriculture and pharmacology.

Types of waxes

Waxes can be natural or synthetic. "Natural" waxes can also have organic or mineral origin, the latter being the product of lignite (coal) processing, which is why they are generally non-renewable (such as petrolatum or petrolatum).

Waxes of animal and / or vegetable origin are considered renewable and modifiable natural waxes, since they can be modified by chemical methods such as hydrogenation and reesterification, for example.

Thus, in the biological context, waxes are classified according to the source from which they are obtained.

- Vegetable waxes

Plants produce different types of waxes in different parts of their bodies: in the leaves, in the flowers, in the fruits or in the seeds.

What is the biosynthetic pathway like?

The aliphatic components of vegetable waxes are synthesized in epidermal cells from fatty acids with very long chains (20 to 34 carbon atoms).

The synthesis begins with the production of fatty acids of 16 and 18 carbons, which are initially originated in the stroma of the plastids thanks to the activity of the soluble enzymes that make up the fatty acid synthase complex.

Subsequently, these fatty acids are elongated thanks to multi-enzyme complexes associated with the membrane known as fatty acid elongases. In each extension of two carbon atoms there are four reactions:

- Condensation between a fatty acyl esterified to an acetyl Co-A molecule (substrate) and a malonyl-CoA molecule

- B-keto reduction

- dehydration

- Enoil reduction

Two main routes for the production of the components of vegetable waxes have been described, one of them is the acyl reduction route and the other is the decarbonylation route. The former results in the synthesis of alcohols and wax esters, while the latter produces aldehydes, alkanes, secondary alcohols and ketones.

Acyl reduction pathway

The acyl-CoA esters produced by chain elongation are reduced in a two-step reaction involving a transient aldehyde-type intermediate and which are catalyzed by the enzyme acyl-CoA reductase. The fatty alcohol produced can be esterified to form a wax ester thanks to the enzyme acyl-CoA alcohol transacylase.

Decarbonylation pathway

The first step in this pathway is the reduction of an acyl-CoA ester to an aldehyde mediated by an acyl-CoA reductase enzyme. When an aldehyde decarbonylase enzyme removes the carbonyl group from said molecule, an alkane is produced, which has one less carbon atom than its precursor fatty acid.

This hydrocarbon can be further metabolized by the insertion of a hydroxyl group in the chain via a hydroxylase or an oxidase, forming a secondary alcohol.

The final step for the production of wax esters from long chain alcohols and fatty acids is catalyzed by an acyl-CoA enzyme: alcohol transacylase, which is also required for the synthesis of triacylglycerols.

- Animal waxes

Animals also produce large amounts of waxes, especially insects, whales, sheep and birds, from which they can be obtained for biotechnological purposes.

Their biological utility has been studied in some detail and, depending on the animal in question, they can serve protection and communication purposes, among others.

Examples of biological waxes

- Animal waxes

Bee wax

As its name implies, this type of wax is produced by bees, the most popular being that of Apis mellifera. These animals have specialized glands in their abdomen that secrete the wax that they use to build the combs where they lay their eggs and organize the hive.

This wax is commonly obtained as a by-product of honey and is used for different purposes, both in cosmetology and in industry (manufacture of candles, polishes, food, textiles, varnishes, etc.). It is made up of hydrocarbons, esters, free acids, and others, and more specialized studies indicate that it is rich in cerotic acid and myricin.

Spermaceti

Sperm whale is another well-known type of animal wax, obtained from a cavity in the head of the Physeter macrocephalus whale, which can produce up to 3 tons of this substance that it uses as sonar.

It is rich in fatty esters, triglycerides, free alcohols and acids; fatty esters include mainly cetyl palmitate (32 carbons) and cetyl myristate (30 carbons).

This animal wax has been widely used in medicine, cosmetology and pharmaceuticals, as well as in the production of candles.

However, some international regulations currently exist, as the whales were killed for the sole purpose of obtaining this product, meaning great losses for the marine fauna.

- Vegetable waxes

Palm wax

The wax palm Copernicia cerifera Martius is a Brazilian palm species that produces one of the most important vegetable waxes from a commercial point of view.

This wax is obtained from the upper and lower surface of the palm leaves and has multiple applications both in food preparation and in cosmetology, furniture and car waxing, the production of waxed dental floss, etc.

Wax palm cultivation (Image by Fernando Arteaga at www.pixabay.com)

Jojoba oil

Jojoba wax is obtained from Simmondsia chinensis, a typical shrub from the arid zones of Mexico and the United States. Its seeds are rich in a wax or oil that is obtained by cold press and that has many medicinal applications, being one of the main replacements for sperm whale.

Seeds of a jojoba plant (Source: Kenneth Bosma / CC BY (https://creativecommons.org/licenses/by/2.0) via Wikimedia Commons)

References

1. Domínguez, E., & Heredia, A. (1998). Waxes: a forgotten topic in lipid teaching. Biochemical Education, 26 (4), 315-316.
2. Firestone, D. (2006). Physical and chemical characteristics of oils, fats and waxes (No. L-0671). Aocs Press.
3. Kolattukudy, PE (1970). Plant waxes. Lipids, 5 (2), 259-275.
4. Lusas, EW, Riaz, MN, Alam, MS, & Clough, R. (2017). Animal and vegetable fats, oils, and waxes. In Handbook of Industrial Chemistry and Biotechnology (pp. 823-932). Springer, Cham.
5. Post-Beittenmiller, D. (1996). Biochemistry and molecular biology of wax production in plants. Annual review of plant biology, 47 (1), 405-430.
6. Tinto, WF, Elufioye, TO, & Roach, J. (2017). Waxes. In Pharmacognosy (pp. 443-455). Academic Press.