We explain what a lipid is and its different functions. In addition, how they are classified and some examples of these molecules.
What is a lipid?
Lipids or fats are sets of molecules formed organic primarily by atoms of carbon, hydrogen and oxygen (to a lesser extent), as well as elements such as nitrogen, phosphorus and sulfur which have the characteristic of being hydrophobic molecules (water insoluble), which they fulfill energetic, regulatory and structural functions in the organisms of living beings.
As a whole, lipids are really diverse, as can be their origins, mostly biochemical, however. They have in common their solvency in non-polar organic solvents (benzine, benzene, chloroform, etc.) and be formed by aliphatic chains (saturated or unsaturated), which sometimes have the form of an aromatic ring.
Its flexibility or stiffness will depend on its molecular structure , but usually these are hydrocarbon 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 accept the interaction with water atoms, or the like. This gives them versatility and importance when it comes to being a structural part of organisms.
Lipids, finally, are a vital part of the diet of living beings , since many vitamins cannot be assimilated except in the presence of certain lipids, and in addition many fatty acids are indispensable for animal metabolism .
At the same time, certain lipids form adipose tissue , commonly known as fat, which plays an important role of support, protection and energy storage for the animal organism, although produced in excess can also constitute a threat to the balance of the lifetime.
Lipids fulfill the following functions in the body:
- Biochemical energy reserve . Certain lipids known as triglycerides (three sugar molecules) constitute in the body of animals (including humans) the energy reserve par excellence. When there is excess carbohydrate, fat is generated to store and consume this glucose in the future, since a gram of fat can provide 9.4 kilocalories to the body.
- Structural support of the body . Lipids serve as a raw material in the construction of numerous biological structures (such as cell membranes), but also as a matter of fixation and physical protection of 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 for regulating various body responses.
- Transportation . Together with bile acids and lipoproteins, lipids go from the intestines to their different destinations, serving as well as transport to other nutrients.
- Protection thermal . Body fat defends the inside of the organism from the action of cold, since the greater the fat, the less thermal radiation out, and therefore less heat loss.
Lipids or fats are classified, in principle, into two categories:
Saponifiable . Lipids similar to waxes and fats are thus known, which can be hydrolyzed as they have ester bonds. Examples are fatty acids, acylglycerides, cerids and phospholipids. In turn, they can be classified as:
- Simple . Its structure mostly comprises oxygen, carbon and hydrogen atoms. Acylglycerides stand out in this group: those that when solidified are known as fat and when they become liquids as oils.
- Complex . Those that possess besides the mentioned atoms, abundant particles of nitrogen, sulfur, phosphorus, or other molecules like carbohydrates. They are also known as membrane lipids.
Not saponifiable . Those that, of course, cannot be hydrolyzed by not having ester bonds.
Some examples of lipids are:
Saponifiable lipids :
- Fatty acids . Long molecules in the form of a hydrocarbon chain (CH2), with a terminal hydroxyl molecule and several carbon atoms (2-4) in the middle. They can be of two types: saturated fatty acids (composed of single bonds only) such as lauric acid, palmitic acid, margaric acid, arachidic acid, etc. or unsaturated fatty acids (with the presence of double bonds more difficult to dissolve) such as oleic acid, linoleic acid, palmitoleic acid, etc.
- Acylglycerides . These are fatty acid esters with glycerin (glycerol), the product of a condensation reaction that can store one to three fatty acids in this way: monoglycerides, diglycerides and triglycerides, respectively. The latter are the most important of all and those that form adipose tissue.
- Phospholipids . Phosphatidic acid contains a glycerol molecule to which up to two fatty acids (one saturated and one unsaturated) and a phosphate group can be attached, which gives a marked polarity to these types of compounds. These types of lipids are the “brick” base for cell membranes: choline, ethanolamine, serine, etc.
Lipids in saponifiable :
- Terpenes . Lipids derived from isoprene, of which they have at least two molecules. Some essential oils such as menthol, limonene, geraniol or chlorophyll phytol are terpenes.
- Steroid . Lipids composed of four fused carbon rings, forming a molecule with hydrophilic and other hydrophobic parts, such as bile acids, sex hormones, vitamin D and corticosteroids. They fulfill regulatory or activating functions in the organism.
- Prostaglandins . Lipids derived from complex essential fatty acids, such as omega-3 and omega-6, forming molecules of 20 atoms that fulfill mediating functions of the central nervous system , the immune system and inflammatory processes.