Waxes

Waxes belong to the second group of neutral lipids. They have more physiological importance even though they are a minor component of biological systems. The wax structure contains a long-chain fatty acid, which is linked through as ester oxygen to long-chain alcohol. The molecules of waxes lipids are completely insoluble in water. They remain solid at biological temperatures. As the structure and function of waxes are hydrophobic in nature. Some plants, feathers, cuticles of certain insects are utilizing waxes as repellents of water. 

Many microscopic aquatic plants and animals are using waxes as energy storage substances. Some marine plankton apparently uses the biosynthesis of waxes to adjust their buoyant density in the depth of the ocean. Many researchers are found that the major source of petroleum present in the deep -sea is originated from the dead and decomposed materials of wax-rich planktons over a vast period. Many fishes and whales are also storing large quantities of waxes in it. 

Plant Waxes 

In the epidermal cells of the plant leaves, the cutin layer, which looks like a cell wall structure, covers the plasma membrane of the cells. Then the cutin layer was finally coated with the thin layer of hydrophobic waxy material. The waxes lipids look like microcrystalline form the outermost boundary of the cuticular membrane. These waxes act as interfaces between the atmosphere and plants. The example of waxes are, that present in the upper layers of eyes have many functions like it limits the diffusion of water and solutes, controls gas exchange, attracts insects for pollination..etc. The waxes around the plants provide protection from diseases, ultraviolet light, and insects. The structure and function of waxes also resist drought and protect plants from environmental stresses. As plants cover the wide space of the earth, the plant waxes are generally considered an abundant source of natural lipids. The waxes in the cutin layer have a complex polyester with linear and branched chains. Which consists of mono or di or trihydroxy fatty acids with α,ω-dicarboxylic fatty acids.

The Below Table Shows the Common Wax Constituents in Some Plant Species.

Animal Waxes 

The main wax production source in mammals is the sebaceous glands on the skin. Most of the sebaceous glands contain hair follicles. Likewise, meibomian glands, which have a similar structure to sebaceous glands are present in the eyelids. Sebaceous glands present on the surface of the skin secrete non-polar lipids namely sebum, where they can easily clear during analysis.  In human beings, the sebaceous glands are distributed throughout the body, except the palm and sole of the foot.  The sebaceous glands are of three types.  The peripheral undifferentiated cells usually produced lipid bodies and lysing cells load their lipids and empty into the lumen. Many research studies have shown that a wide range of lipid classes are present and they will vary depending on nature and species type. The human sebum’s chemical composition is completely different from other species. Particularly, they contain a high amount of triacylglycerols and natural fatty acids. 

The above table shows the relative composition of non-polar lipids secreted from the skin of various species. 

The waxy substance that coats the skin of the human fetus and newborns are produced during the third trimester of gestation.  This waxy substance is known as vernix caseosa. Inside the uterus, it acts as a waterproof, protective agent and controls the flux of water across the skin. Further, it facilitates the final stage of skin development.  After birth, it acts as a skin protector to fight against bacterial attack and helps the baby to exposure to the air. 

The grease substance obtained on the wool of sheep during the refining process is termed wool wax or lanolin. Lanolin is the only animal wax, which has its commercial value. They are mainly derived from the sebaceous glands and/or stratum corneum of the skin. These waxes are rich of wax esters. I.e 1- and 2-alkanols and of 1,2-diols

Other Animal Waxes 

Meibomian glands are the holocrine glands, which are located in the upper and lower eyelids of human beings and many other animals. They secrete oily, lipid-rich substances known as meibum. The chemical composition of lipids will vary depends on the species. They protect the eyes from bacterial infections and dryness of eyes. 

Harderian glands located deep in the orbit of the eyeballs, which can be identified from most of the terrestrial vertebrates. They possess protective translucent third eyelids, which is known as the nictitating membrane. Harderian glands are the exocrine glands.

Marine Waxes: Most of the marine animals from whales to invertebrates contain a specific amount of waxes. They are formed mainly composed of hydrocarbons and wax esters. Some species will contains glycerol ethers and sterols in their waxes. The waxes in the fishes are serving energy sources for insulation, buoyancy, and even echolocation. Zooplanktons will have a large number of wax esters and it acts as a major contribution to the marine food chain. 

Insect Surface Waxes: Insect’s external surfaces are covered by the layer of wax, which are used to restrict the movement of water and helps to provide a physical barrier to protect against abiotic stresses like insecticides, chemicals, and toxins. Biotic stress like an attack of microorganisms, parasites, and other predators. Some lipids help with sexual signaling. 

Bird waxes: The preen glands or the uropygial gland present in the birds have a similar structure as sebaceous glands. They secrete waxes, which are largely composed of wax esters. The waxes in the birds mainly help to produce a water-proof layer to the feathers and protection against microbes. 

Microbial Waxes

Some waxes are found around the microorganisms like bacteria, viruses, fungus..etc. Microbial waxes often accompanied by triacylglycerols. This is known to store foods for many prokaryotic species.  Gram-positive and Gram-negative bacteria are the best examples of waxes in microbes. Gram-negative bacteria will synthesize the biosynthetic wax esters when the corban is plentiful with the lack of other essential nutrients such as nitrogen..etc.