Classification of lipids | Functions of lipids

What is lipids?


Lipids include

  • fats,
  • oils,
  • waxes,
  • cholesterol
  • and related compounds.

They are the organic compounds that are insoluble in water, but soluble in organic solvents like ether, alcohol, chloroform and benzene.

Lipids have relatively less oxygen in proportion to carbon and hydrogen than do carbohydrates, therefore they are less soluble in water as compared to carbohydrates.

Classification of lipids

Classification of lipids

Lipids is arranged as

  • acyl glycerol,
  • waxes,
  • phospholipids,
  • sphingolipids,
  • glycolipids
  • and terpenoid lipids including carotenoids and steroids.


Acylglycerol are composed of Glycerol and fatty acids.

Glycerol Is a;

  • 3 carbon alcohol


  • 3 OH groups.
  • A fatty acid is a long straight chain of carbon atoms with the carboxyl group at one end.
  • Glycerol combined with one fatty acid form a monoglyceride.
  • A glycerol combined with 2 fatty acids forms a diglyceride.
  • The most widely spread acyl glycerol is triacyl glycerol, also called triglycerides or neutral lipids which are composed of 1 glycerol and 3 fatty acids linked through ester bonds. Chemically they are esters of fatty acids and alcohol.

Features of fatty acids present in acylglycerol

Fatty acids present in acylglycerol contain even number of carbon atoms, for example acetic acid has 2 carbon, butyric acid has 4 carbon, palmitic acid has 16 carbons and oleic acid has 18 carbons.

They may contain no double bonds (saturated fatty acids) for example acetic acid, butyric acid and palmitic acid or they may contain upto six double bonds (unsaturated fatty acids) for example oleic acid.

In animals the fatty acids are straight chains, while in plants these may be branched or ringed Animal fats contain more calories than vegetable fats.

Solubility of fatty acids in organic solvents and their melting points increase with increasing number of carbon atoms in the chain. Palmitic acid is much more soluble in organic solvents than butyric acid. The melting point of palmitic acid is 63.1C° while that orbit attic acid is -8C°.

Fats containing unsaturated fatty acids are usually liquid at room temperature and are said to be oils. for example oleic acid. Fats having saturated fatty acids are solids.

Animal fats are

  • solid at room temperature


  • plant fats are liquids.

They are not crystalline, but some can be crystallized under specific conditions.


  • Waxes are esters of fatty acids and alcohols with both fatty acids and alcohols having long chains.
  • They are lipids with odd number of carbons ranging from C25 to C35.
  • They are widespread as protective coatings on fruits and leaves , protecting plants from water loss and physical damage.
  • Some insects also secrete wax. Wax also provides protective barrier for insects, birds and animals such as sheep.


Phospholipid are derivatives of phosphatidic acid.

Phosphatidic acid Themselves are composed of glycerol, fatty acids and phosphoric acid. A nitrogenous base bonded to phosphatidic acid forms a phospholipid. Nitrogenous bases such as choline, ethanol amine and serine are important components of phospholipid. They are present in

  • bacteria,
  • animal
  • plant cells
  • and are frequently associated with membranes.

Each phospholipid molecule has a polar hydrophilic region that contain phosphate And non polar hydrophobic region that contains fatty acids.

Phospholipids form the lipid bilayer of membranes. In the formation of lipid bilayer, phospholipid molecules orients itself in such a way that its polar head faces water and its non polar tails face each other in the centre such that tails are never in contact with water. The lipid bilayer formed by phospholipid is a fluid.


Terpenoids are made-up of simple repeating units called isoprenoid units. This unit by condensation (polymerizationl in different ways give rise to compound such as rubber, carotenoids, steroids, terpenes etc.


  • Steroids are lipid that do not contain fatty acids. These are complex molecules with four interlocking carbon rings, three are six sided rings and the 4th one is  a 5 sided ring.
  • Steroids are important to our bodies in many ways.
  • The male and female sex hormones and adrenal gland hormones are steroids.
  • Vitamin D that helps to regulate calcium metabolism is a steroid.
  • Cholesterol that is an important component of membranes and nervous tissue is a steroid.

  • Bile acids that help in digestion and absorption of fats are also steroids.


Vitamin A is made up of carotenoid pigments of plants. The major source of vitamin A are egg yolk, green and yellow vegetables, fruits, liver and butter. The function of vitamin A is formation of visual pigments, maintenance of normal epithelial structures. Deficiency of vitamin a causes night blindness and skin legends.


Terpens (from turpentine) includes

  • essential oils
  • such as
  • citral,
  • comphor,
  • menthane,
  • the resin acids and rubber.

Functions of lipids

Functions of lipids

Lipids are used to store energy. Because of higher proportion of carbon hydrogen bonds and very low proportion of oxygen, lipid store double the amount of energy as compared to the same amount of any carbohydrate.

Some lipids give insulation against

  • atmosphere,
  • heat
  • cold
  • and also act as waterproof material.

Learn more

What is lipid for mdcat preparations

Classification of lipids for MDCAT preparation

What is lipids?

Classification of lipids

What is acylglycerol?

Features of fatty acids present in a acylglycerol

What is waxes?

What is phospholipids?

What is terpenoids?

What is steroids?

What is carotenoids?

What is terpenes?

Functions of lipids

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