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Fats and oils predominantly are tri esters of glycerol and aliphatic fatty acids containing up to 22 carbon atoms. Waxes are esters of long chain fatty acids usually containing 24-28 carbon atoms, with long chain primary alcohols or with alcohols of the steroid group.

The general classes of lipids are neutral lipids, glycolipids and phospholipids occur in most species. Glycolipids are notably absent from many Mycoplasma species. Generally, the percentage by weight of phospholipids equals the combined percentages of neutral and glycolipids. 

Lipids are defined as those biological molecules readily soluble in organic solvents such as chloroform, ether or toulene. However, some very hydrophobic proteins such as the ATP synthase are soluble in chloroform and lipids with large hydrophilic domains such as lipopolysaccharide are notsoluble in these solvents.


What are Lipids?

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The lipids are a large and diverse group of naturally occurring organic compounds. They are soluble in non polar organic solvents like ether, chloroform, acetone & benzene, and generally insoluble in water. Though there is great structural variety among the lipids, the property of their solubilities put them in one group of compounds. Lipids are one of the very important groups of compounds that are involved in the life of an organism. The lipids are divided into sub groups depending on their functional characteristics. 

They are Fatty acids, Fats and oils ( saturated or unsaturated), Soaps and detergents, waxes, Phospholipids, eicosonoids, terpenes, steroids, lipid soluble vitamins and bio synthetic pathways. Each lipid has a different structure. All the lipids have a large number of Carbon hydrogen bonds which will make them highly energy rich.

Structure of Lipids

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Every Lipid has a different structure. But they all have a large number of carbon hydrogen bonds. The length of the chain which is generally linear is less than the chain length of proteins. In other words, the molecular mass of lipids is in between amino acids and proteins.

Fatty acids are straight chains with carbon chains having 12-20 carbon atoms. They have a terminal carboxylic group and may be saturated or unsaturated. Fats and oils are also both saturated as well as unsaturated. They are the triglycerides (ester) formed out of the combination of glycerol ( 1,2,3- tri carboxy propane.) with fatty acids. Hence their molecular formula is roughly thrice that of concerned fatty acid.

Soaps and detergents are with 30-35 carbon atoms in a chain and are metallic esters. Terpenes are multiples of isoprene units. Steroids are cyclic compounds. Phospholipids which are part of the cell membrane are having the phospate ester end to a large fat chain. This is also called sandwich membrane since the phospho end keeps the fat in between their layers.

Metallic Esters

Steroids Cyclic Compounds


Natural rubber is another lipid with a number of isoprene units.

Natural Rubber Lipid

Vitamins are having both fatty acid and steroid type of structures. Some of the structures are shown below.

Lipid Soluble Vitamins

Function of Lipids

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Triglycerides provide the energy during aerobic metabolism. These triglycerides are stored in the adipose (fat) tissues of the body beneath the skin, within skeletal muscles and around organs. In plants like algae, the hydrophobic triglycerides act as media to keep water away from the surface to enable the activity of chlorophyll. The hydrophilic lipids help the clusters to grow together. Cholesterol is the basic lipid that provides structure for steroid hormones, such as estrogen and androgen, cell membranes, and bile acids. The fluid balance within the cell and its outside fluid environment is regulated by these. Fats in the body helps to cushion the organs from shock and also act as energy store.

Recent studies show that the lipids help in sending vital signals to the other metabolic activities sensing the deficiencies. The metabolic activities like calcium mobilization, growth, reproduction, and controls like blood pressure, enzymatic actions etc.are monitored by the lipid signalling. Fat soluble vitamins like Vitamin A, Vitamin K and Vitamin E are carried in the body by the fat which is also a lipid.
Lipids are most important part of the biological activity.

There are variety of types of lipids. They can be classified as follows.
Fat producing Lipids: These are called Fatty acyls which are formed by the chain elongation with the catalytic acetyl co enzyme and malonyl co enzyme. These fatty acyls give rise to various important fatty acids like eicosonoides, thromboxanes and prostaglandins.

Glycerolipids or triglycerides: These are the type of lipids which act as storage lipids because they store the energy in the form of fats in the body.

Glycero phospholipids: These are also called phospholipids and these are main components of the bi layered cell membrane. These lipids also involve in signaling for other activities and even the nerve impulses.

Sterol lipids: These are the hormone class of lipids. Hormones like Cholesterol and Estrogen and testosteron are the compounds belonging to this class. Fat soluble vitamins like vitamin K and Vitamin A are belonging to these lipid class.
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Examples of Lipids

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Lipids are one of the most predominant components of life. Though it cannot be synthesized by body it is present in various sources and can be stored in the body. Some of the sources of lipids are listed below.
  1. Edible Oils: Oils extracted from peanuts, rice bran, corn, olive, sunflower kernels, cottonseed, and vegetable oils etc., are high on lipids. Oils from most of the sources contain mono unsaturated fats that are difficult to digest and are bad for health. Cod liver oil and whale oil are also lipid examples which are not good for health and should not be consumed. Cheese, cottage cheese, margarine, butter, cream like milk products are high on fats.
  2. Nuts: Peanuts, cashew nuts, almonds, walnuts etc. contain lipids which are not harmful and they help in cell growth. They contain saturated fats that are easy to digest.
Many vegetables, grains, and fruits also contain lipids.

In the body, the bilayered cell membrane is phospholipid. Steroids such as cholesterol and cholic acid. Prostaglandins, thromboxanes and leukotrienes are also lipids. Fat soluble vitamins like vit.A and Vitamin K are lipids.

Soaps and detergents that contain sodium stearate, sodium dodecyl benzene sulphonate etc are the lipids. Waxes like bee wax are examples of lipids. Gutta percha, natural rubber, terpenes like camphor alpha terpene, geraneol are some examples of lipids.

Functions in Biosystem

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Lipids perform several important functions in biosystems.
  1. Phospholipids are the constituents of cell mebrane and regulate membrane permeability.
  2. Phospholipids are also used as detergents to emulsify fat for transport within the body.
  3. They act as cellular metabolic regulators.
  4. They protect internal organs, serve as insulating materials and give shape and smoothness to the body.
  5. They serve as a source of fat soluble vitamins.
  6. Essential fatty acids are useful for transport of cholesterol, formation of lipoproteins, etc.
  7. Triacyl glycerols are the concentrated fuel reserves of the body.
  8. Phospholipids in mitochondria are responsible for confirmation of electron transport chain components.
  9. Accumulation of fat in the liver is prevented by phospholipids.
  10. Phospholipids help in removal of cholesterol from the body by participating in reverse cholesterol transport.
  11. Cholesterol is a constituent of membrane structure and it synthesizes bile acids, hormones and vitamin D. It is the principal sterol of higher animals, abundant in nerve tissues and gallstones.
More topics in Lipids
Types of Lipids Cholesterol Structure
Phospholipids Omega 3 Fatty Acids
Trans Fatty Acids Micelle
Monomer of Lipids
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