• Lipids are a heterogeneous group of organic compounds made of carbon, hydrogen and a few atoms of oxygen.
  • The term lipid is derived from greek word lipos, meaning fat.
  • These substances are not soluble in water but dissolve in non-polar solvents such as benzene, ether, chloroform. This is because they contain long hydrocarbon chains that are non-polar and thus hydrophobic.
  • The main groups of compounds classified as lipids are triglycerides, phospholipids, steroids and waxes.

(i) Oils

  • They are esters of fatty acids with glycerol and are liquids at room temperature.
  • They are rich in unsaturated fatty acids.
  • They have a low melting point.
  • They are more reactive and easily digestible than fats, hence doctors advise intake of oils more than fats.

e.g. Mustard oil, sunflower oil, rape seed oil, sesame oil.

(ii) Fats

  • They are esters of fatty acids with glycerol and are solids at room temperature
  • They are rich in saturated fatty acids.
  • They have a high melting point.
  • They are less reactive and gets deposited in the blood vessels, hence doctors advice not to include more of these in our diet

e.g., Butter, Ghee, Vanaspati.

(iii) Waxes

  • They are esters of fatty acids with a long chain alcohol, but not glycerol.
  • They form water insoluble coatings on hair and skin of animals and on leaves, stems and fruits of plants and provide protection.

(iv) Phospholipids

  • They are compound lipids and have a phosphate group along with fatty acids and alcohol (glycerol).
  • It serves as major structural component of cell membrane
  • These lipids have both hydrophobic and hydrophilic regions.

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(v) Glycolipids

  • They have one or more sugars (carbohydrates) along with the fatty acids and alcohol (glycerol).

e.g., Cerebrosides (white matter) and Gangliosides (grey matter).

(vi) Sphingolipids

  • They have amino-alcohols in their molecules instead of glycerol e.g., sphingomyelin in brain cells.