Lipid

We explain what a lipid is and its different functions. Also, how they are classified and some examples of these molecules.

What is a lipid?

Lipids are sets of organic molecules made up primarily of carbon, hydrogen, and oxygen atoms (to a lesser extent), and other elements such as nitrogen, phosphorus and sulfur. Lipids are hydrophobic molecules (insoluble in water), but they are soluble in nonpolar organic solvents, such as benzine, benzene, and chloroform.

They can be formed by aliphatic chains (saturated or unsaturated) or aromatic rings. They are very diverse compounds due to their molecular structure: some are rigid, others are flexible and generally have linked chains linked by hydrogen bonds.

Some lipids, such as those that make up the cell membrane, have a hydrophobic and a hydrophilic layer, so that only on one side can they interact with water molecules or similar. This gives them great versatility and importance when it comes to forming a structural part of organisms.

The lipids are a vital part of the diet of living beings since many vitamins cannot be assimilated unless they are in the presence of certain lipids. Furthermore, many fatty acids are essential for animal metabolism.

At the same time, certain lipids form adipose tissue (commonly known as fat), which plays a role of support, protection and energy storage of utmost importance for the animal organism, although produced in excess can also constitute a threat to the balance of life.

Function of lipids

Lipids fulfill the following functions in the body:

• Energy reserve of the animal organism. Certain lipids known as triglycerides (three sugar molecules) constitute the energy reserve par excellence in the body of animals (including humans). When there is excess carbohydrates, fat is generated to store and consume said glucose in the future since one gram of fat can provide 9.4 kilocalories to the body.
• Structural support of the body Lipids serve as raw materials in the construction of numerous biological structures (such as cell membranes). They also serve as a material for fixing and physically protecting internal organs and different parts of the body.
• Regulation and cellular communication Various vitamins, hormones and glycolipids are nothing more than fats secreted by various organs and ganglia of the body, which uses them as a mechanism to regulate various responses of the body.
• Transport Together with bile acids and lipoproteins, lipids go from the intestines to their different destinations and serve as transport for other nutrients.
• Thermal protection. Body fat defends the interior of the body from the action of cold since the more fat there is, the less thermal radiation to the outside and, therefore, less heat loss.

Classification of lipids

Lipids or fats are classified, in principle, into two categories:

• Saponifiable Lipids similar to waxes and fats, which can be hydrolyzed because they have ester bonds. For example: fatty acids, acylglycerides, cerides and phospholipids. In turn, they can be classified into:
  • Simple Its structure mainly comprises oxygen, carbon and hydrogen atoms. For example: acylglycerides (which when solidified are known as fat and when liquid are known as oils).
  • Complexes They have (in addition to the aforementioned atoms) abundant particles of nitrogen, sulfur, phosphorus, or other molecules such as carbohydrates. They are also known as membrane lipids.
• Not saponifiable Lipids that cannot be hydrolyzed because they do not have ester bonds.

Examples of lipids

saponifiable lipids:

• fatty acids They are long molecules in the form of a hydrocarbon chain (-CH₂-), with a terminal carboxyl group (-COOH) and several carbon atoms (2-24) in the middle. They can be of two types:
  • Saturated fatty acids Composed of simple links only. For example: lauric acid, palmitic acid, margaric acid, arachidic acid, etc.
  • Unsaturated fatty acids With the presence of double bonds that are more difficult to dissolve. For example: oleic acid, linoleic acid, palmitoleic acid, etc.
• Acylglycerides. They are esters of fatty acids with glycerin (glycerol), the product of a condensation reaction that can store one to three fatty acids: monoglycerides, diglycerides and triglycerides, respectively. The latter are the most important of all and are what form adipose tissue.
• Phospholipids Phosphatidic acid contains a glycerol molecule to which up to two fatty acids can be attached (one saturated and one unsaturated) and a phosphate group, which gives a marked polarity to this type of compounds. These types of lipids are the basic “brick” for cell membranes: choline, ethanolamine, serine, etc.

Unsaponifiable lipids:

• Terpenes Lipids derived from isoprene, of which they have at least two molecules. For example: some essential oils such as menthol, limonene, geraniol or chlorophyll phytol.
• Steroids Lipids composed of four fused carbon rings, which make up a molecule with hydrophilic and hydrophobic parts, and fulfill regulatory or activating functions in the body. For example: bile acids, sex hormones, vitamin D and corticosteroids.
• Prostaglandins Lipids derived from complex essential fatty acids, such as omega-3 and omega-6. They are made up of molecules with 20 carbon atoms that fulfill mediating functions of the central nervous system, the immune system and inflammatory processes.