Cérides, also known as waxes, arise from the union of a long chain fatty acid (14 to 36 carbon atoms) with a monoalcohol, also long chain (16 to 30 carbon atoms), through a ester bond. The result is a completely apolar molecule, very hydrophobic, since no charge appears and its structure is of considerable size.
This characteristic allows the typical function of waxes to be waterproofing. The layer of young leaves, fruits, flowers or petals, and the integuments of many animals, hair or feathers, are covered with a waxy coating to prevent the loss or entry (in small animals) of water.
The phospholipids are a large group of molecules having C, H, O, N and P in common. They are formed by an alcohol, to which they are attached, by ester bond, fatty acids and phosphoric acid, which gives them their name. On this basic molecular skeleton we can consider some variations that give rise to the phospholipid groups of greatest biological interest: phosphoacylglycerides and phosphoesphingolipids.
Phosphoacylglycerides are composed of glycerol, two of whose -OH (hydroxyl) groups are attached to two fatty acids via individual ester bonds. The third is related to the phosphate group, also via an ester bond, which in this case is commonly referred to as the "phosphoester bond". This molecular nucleus constitutes phosphatidic acid. In turn, another molecule can bind to phosphate (we can represent it by X), which determines the different groups of phosphoacylglycerides. Among the most important are:
- Lecithins, if X is the choline amino alcohol. They are very abundant in egg yolk, where they are obtained for cosmetic and dietary purposes.
- Encephalins, if X is the amino alcohol ethanolamine or the amino acid serine. They abound in the brain, from where they were first obtained, but also exist in other organs such as the liver.
- Cardiolipins, if X is the alcohol glycerol, in turn, linked to another phosphoric acid and a diglyceride. The molecule is therefore symmetric. They abound in the heart muscle.
Within each group, in turn, there are different types depending on what the specific fatty acids are (generally one saturated and the other unsaturated), which further expands the variety of molecules.
Phosphoesphingolipids are made up of the alcohol sphingosine instead of glycerol. Sphingosine is a long-chain amino alcohol, to which a fatty acid binds, forming a compound called ceramide, which is the central nucleus of this and other groups of lipids. Therefore, it can be said that they are made up of ceramide and phosphoric acid. The most important are sphingomyelins, made up of ceramide, phosphoric and choline. They form the myelin sheaths of neurons.
