Question

How can lipids be distinguished from sugars?

Answer 1

Hint: Lipids and sugars are the basic building blocks of biomolecules for a living cell or organism. Lipids are nonpolar organic fatty acids or their derivatives, like fat, waxes, oils. Where sugars or carbohydrates are naturally occurring carbonyl compounds also referred to as saccharides. The water-soluble and sweet-tasting carbohydrates are generally called sugars.

Complete answer:
Distinguishing lipids from sugar can be done by a simple property test, that is hydrophobicity test or in simple terms, water solubility test. Generally, there are two types of molecules present: one is hydrophobic, which means the molecule is not attracted towards the water and is insoluble in water. And the second one is hydrophilic molecules that are water-soluble in nature.

As we know that the sugar is a form of carbohydrates and these are basically hydrates of carbon, polyhydric compounds. If you observe the structural configuration of sugar, you can notice the presence of hydroxyl groups (OH). This hydroxyl group is capable of making a hydrogen bond with a water molecule, which results in the water affinity of sugar and makes it water-soluble.

Whereas, the lipid is mostly long-chain free fatty acids which are attached to glycerol by the means of the ester linkage. The free fatty acid group which is present in the lipid contributes to its hydrophobicity. That’s why lipid is insoluble in water.

By this simple solubility test, we can distinguish between lipid and sugar. If the substance is soluble in water, then it can be sugar, or else it is a lipid.

Note: Some lipids like glycolipids, where sugar moiety is present, and phospholipids, where a phosphate group is present, are sparingly soluble or insoluble in water. The ester bond present in lipids is of polar nature and capable of making a hydrogen bond with a water molecule. But the hydrophobicity of the fatty acyl group overcomes this polar nature and makes lipids insoluble in water.