Carbohydrate Structure

Carbohydrates are one of the most important food groups in the diet of all animals, including humans. They provide essential elements that the body needs for instant energy production and various vital functions.


Carbohydrates are macromolecules composed of carbon (C), hydrogen (H) and oxygen (O) and have the general formula of Cx(H2O)y.

Carbohydrates are classified based on the following:

  • The number of carbons
  • The number of sugar units
  • Location of the carbonyl (C=O) group
  • The molecules’ stereochemistry or chiral handedness – This refers to the configuration of the molecule, which may exist in different structural forms or isomers.

Classification by sugar number

When classified according to the number of sugars, carbohydrates are described as follows:

Monosaccharides - These consist of a single sugar unit. Examples include glucose, fructose, and glyceraldehyde. Depending on the number of carbon atoms, the molecule may be a triose, tetrose, pentose or hexose.

Disaccharides - These contain two sugar units.

Oligosaccharides - These are made up of 3 to 10 sugar units.

Polysaccharides - These contain more than 10 sugar units and may be storage polysaccharides such as starch or glycogen or structural polysaccharides such as the cellulose found in plant cell walls. Structural peptidoglycans are polysaccharides that found in the bacterial cell wall.

Monosaccharides and disaccharides are considered simple sugars as they break down easily, readily providing the body with energy. Oligosaccharides and polysaccharides are more complex molecules and are referred to as complex carbohydrates.

Further Reading

Last Updated: Aug 23, 2018

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


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