Biomolecules: Classification and Structure of Lipids, Biological Importance of Lipids (For CBSE, ICSE, IAS, NET, NRA 2022)

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Classification of Lipids

Lipids are classified into three broad categories on the basis of their molecular structure and the hydrolysis products.

  • Simple Lipids: Those lipids which are esters and yield fatty acids and alcohols upon hydrolysis are called simple lipids. They include oils, fats and waxes.
  • Compound Lipids: Compound lipids are esters of fatty acids and alcohol with additional compounds like phosphoric acid, sugars, proteins etc.
  • Derived Lipids: Compounds which are formed from oils, fats etc. during metabolism. They include steroids and some fat-soluble vitamins.

Structure of Lipids

Simple Lipids

The simple lipids are esters. They are subdivided into two groups, depending on the nature of the alcohol component. Fats and oils are triglycerides, i.e.. they are the esters of glycerol with three molecules of long chain fatty acids.

Simple Lipids
  • Compound Lipids: Compound lipids on hydrolysis yield some other substances in addition to an alcohol and fatty acids. The first type of such lipids are called phospholipids, because they are the triglycerides in which two molecules of fatty acids and one molecule of phosphoric acid are present.
  • Derived Lipids: Steroids are another class of lipids which are formed in our body during metabolism. These are the compounds with a distinctive ring system that provides the structural backbone for many of our hormones. Steroids do not contain ester groups and hence cannot be hydrolyzed.
Simple Lipids

Biological Importance of Lipids

  • Fats are main food storage compounds and serve as reservoir of energy.
  • Presence of oils or fats is essential for the efficient absorption of fat-soluble vitamins A, D, E and K.
  • Subcutaneous fats serve as biological insulator against excessive heat loss.
  • Phospholipids are the essential component of cell membrane.
  • Steroids control many biological activities in living organisms.
  • Some enzymes require lipid molecules for maximum action.

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