Lipids are esters of long chain fatty acids. These are a diverse group of naturally-occurring organic compounds, such as fat, waxes, sterols, glycerides and phospholipids (Figure 27).

Figure 27. Types of lipids
Figure 27. Types of lipids

These compounds are similar to each other as they are soluble in non-polar organic solvents (e.g. ether, chloroform, acetone & benzene) and insoluble in water.

Characteriscs of Lipids

Lipids are broadly defined as hydrophobic or amphiphilic molecules. Due to their amphiphilic nature, they form structures, such as, vesicles or liposomes.

The main biological functions of lipids is energy storage. They also act as signaling molecules and form structural components of the cell membrane.

Most of lipid found in food is in the form of triacylglycerols, cholesterol, and phospholipids.

Eicosanoids, such as prostaglandins (Figure 23), leukotrienes, and thromboxanes are biologically important fatty acids.


These are a group of naturally occurring, chemically-related fatty acids derived from arachidonic acid (Figure 28).

Figure 28. Structure of prostaglandin
Figure 28. Structure of prostaglandin

They participate in a wide range of body functions, such as, contraction and relaxation of smooth muscle, constriction and dilation of blood vessels, control of blood pressure, and modulation of inflammation.


These (Figure 29) are lipids that are important constituents of inner mitochondrial membrane. They form 20% of the total lipid content.

Cardiolipins play important role in apoptosis and cholesterol translocation. It also has an anticoagulant properties.

Figure 29. Structure of cardiolipin
Figure 29. Structure of cardiolipin

Applications of Lipids

Lipids play three major roles in cells.

  • These provide an important form of energy storage.
  • Lipids are the major components of cell membranes.
  • They play important roles in cell signaling —  as steroid hormones as well as messenger molecules that convey signals from cell surface receptors to the targets within the cell.
  • Glycerophospholipids, phospholipids, and sterol lipids form key components of the biological membrane.
  • Waxes are esters of fatty acids with long chain monohydric alcohols found in leaves, fruits, feather of birds, and fur of animals providing protection from dehydration.