Also known as fats, they perform multiple functions in the body.
Fats are broken down in the digestive tract to form individual fatty acids and cholesterol molecules.
Fatty acids and cholesterol are key components of the membranes that surround all cells. The cholesterol may also be used to create many other compounds in the body, such as steroid hormones.
Finally, fatty acids represent an important source of energy, particularly for long-term storage purposes.
Classification of lipids
They can be classified based on their physical properties at room temperature (solid or liquid, respectively fats and oils), based on polarity or their essentiality for humans, but the preferable classification is based on their structure.
According to the structure, they can be classified into three main groups.
They consist of two types of structural remains. They include:
- Glyceryl esters which are esters of glycerol and fatty acids: eg triacylglycerols, mono and diacylglycerols.
- Cholesteryl esters which are esters of cholesterol and fatty acids.
- Waxes that are esters of long-chain alcohols and fatty acids, so they include esters of vitamins A and D.
- Ceramides which are fatty acid amides with long chain di or trihydroxy bases containing 12-22 carbon atoms in the carbon chain: e.g. sphingosine.
They consist of more than two types of structural remains. They include:
- Phospholipids which are glycerol esters of fatty acids.
- Phosphoric acid and other nitrogen-containing groups.
- Phosphatidic acid which is diacylglycerol esterified to phosphoric acid; phosphatidylcholine which is phosphatidic acid bound to choline, also called lecithin.
- Phosphatidylethanolamine; phosphatidylserine.
- Phosphatidyl acylglycerol in which more than one glycerol molecule is esterified to phosphoric acid, cardiolipin, and diphosphatidyl acylglycerol.
- Glycoglycerolipid which is 1,2-diacylglycerol linked by a glycosidic bond through the sn-3 position with a carbohydrate residue.
- Gangliosides which are glycolipids that are structurally similar to polyhexoside ceramide and also contain 1-3 sialic acid residues.
- Most contain an amino sugar in addition to the other sugars.
- Sphingolipids, derived from ceramides.
- Sphingomyelin which is phosphorylcholine ceramide.
- Cerebroside, are monohexoside ceramides that are linked by ceramide to a single sugar residue at the terminal hydroxyl group of the base).
- Ceramide di- and polyhexoside which is bound respectively to a disaccharide or a tri- or oligosaccharide.
- Cerebroside sulfate which is ceramide monohexoside esterified to a sulfate group.
Derived lipids are produced as such or are released from the other two main groups due to hydrolysis which are the building blocks of simple and complex lipids include:
- Fatty acids and alcohols.
- Fat-soluble vitamins A, D, E and K.
- Fats serve as a food reserve, in plants and animals. Hibernating animals store extra fat before the onset of winter. Migratory birds also do it before migration.
- They work like concentrated foods because, compared to carbohydrates, they yield more than twice the energy per unit of weight (9.3 kcal / gm: 4.5 kcal / gm).
- Fats can be turned into carbohydrates. Therefore, the fats stored in oilseeds (for example, peanuts, mustard, castor, sunflower, cotton and coconut) provide not only energy but also raw materials for the growth of the embryo.
- In seeds and spores, lipids help in thermal insulation, protection against ultraviolet radiation and loss of water.
- Vitamins A, D, E, and K are fat soluble. The latter not only act as their carriers but also protect them from oxidation.
- In animals, fat occurs as droplets inside cells called adipocytes. The adipocytes of cold-blooded or poikilothermic animals have a higher amount of unsaturated fatty acids compared to warm-blooded or homoerothermic animals.
- Fatty or fatty tissue forms an insulating layer under the skin of animals to protect it from the low temperature. The whale has a very thick layer of subcutaneous blubber called blubber. Animals from colder regions also have a thick fat layer for insulation, for example, polar bear.
- Subcutaneous fat rounds the contours of the body of animals and humans. In animals, fats produce a cushion around the eyeballs, gonads, kidneys, and other vital organs.
- Edible oils extracted from many seeds are used in cooking. The animal fats present in the production of milk, butter and ghee.
- Vegetable oils are used as a low-cholesterol fat. They are also hydrogenated to form vegetable ghee.
- The soap was previously made from animal fat. Today, vegetable fats are used for this purpose.
- Drying oils that have unsaturated fatty acids are used in the paint industry.
- The waxes form a protective layer on the fur of the animal. They protect the floating leaves of aquatic plants against moisture. In land plants, they reduce the rate of transpiration.
- The myelin sheath around nerve fibers participates in insulation.
- Phospholipids, glycolipids, and sterols are components of cell membranes.
- The fragrance of many plant products is due to fat-like substances called terpenes.
- In birds, oil from the gland is used to lubricate the feathers and protect them from moisture. Hair is similarly lubricated in mammalian skin. Prevents your felt. The skin is also protected from dryness.
- Desert animals use fat as a source of metabolic water, eg Kangaroo Rat, Camel. Kangaroo or Desert Rat does not drink water. Camel uses the fat stored in its hump to obtain metabolic water during extreme drying conditions.