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Carbohydrates play an important role in many biological processes as energy-storage compounds and also in many recognition functions.

• Simple sugars of five (pentoses) and six (hexoses) carbon centers are termed monosaccharides and they are chiral molecules in which the D-form predominates in mammalian carbohydrates.

• Aldose are monosaccharides having and aldehid group whereas Ketoses have a ketone group. Examples:
  Aldohexose: D-glucose, D-galactose, D-mannose
  Ketohexose: D-fructose

  Aldopentose: D-Ribose

  Ketopentose: D-Xylulose
• Anomers are pairs of sugar molecules differing only in one specific center, for instance alpha- and beta-glucose.

• The open-chain form aids to understanding the mutarotational process, in which two anomers interconvert spontaneously. They can exist as an equilibrium between the open-chain form and as six-membered (pyranose) and/or five-membered (furanose) ring.

• Epimers are isomers that differ in the configuration of one center, for instance, alpha-glucose vs alpha-galactose (C-4 carbon) or alpha-glucose vs alpha-mannose (C-2 carbon).

• Modified monosaccharides:
  Deoxysugars as fucose, deoxyribose or rhamnose
  Glycosides: Result of a reaction between an hydroxyl group and an alcohol. For instance, methyl alpha-D-glucoside results of the reaction of methanol in the position 1 on alpha-glucose:

  Aminosugars that have a nitrogen in the C-2 position, often acetylated, for instance N-acetyl-alpha-D-glucosamine.
  Derivatives formed by oxidation of C-1 or C-6 position to carboxylic acid are termed aldonic or uronic acids, respectively. For instance, gluconic and glucuronic acids results after oxidation of glucose.