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Aldose Vs Ketose: Definition, Differences, Examples

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Definition of Aldoses

A monosaccharide with a carbon backbone as well as a carbonyl group at carbon-1 is known as an aldose.

  • Aldoses have the same general formula as other carbohydrates, Cn(H2O)n. Each hydroxyl group is linked to a carbon atom in the carbon backbone.
  • Since aldoses have an asymmetrical carbon core, they all display stereoisomerism. Depending on the chirality of the asymmetric carbon, these molecules can exist in either L-form or D-form.
  • D-aldoses are aldoses with alcohol groups on the right, whereas Laldoses are aldoses with alcohol groups on the left.
  • Aldoses are polyhydroxy aldehydes that can also take the form of hemiacetals, that have a cyclic ring structure. Carbohydrates containing more than four carbon atoms have a cyclic structure.
  • Since many biological systems can only employ one enantiomer of a carbohydrate, aldoses are often given names that reflect their stereoisomerism.
  • Aldoses can also tautomerize into ketoses via a dynamic process involving the production of an enol intermediate. Tautomerization can be reversed, as well as the aldo-form is typically more stable than the enol-form.

Definition of Ketosis

A ketose is a monosaccharide that contains a carbon backbone as well as a carbonyl group inside it.

  • The general formula for ketoses is RCOR’, where R is an alkyl group that may or may not be the same as the other R’.
  • Since monosaccharide ketoses may be tautomerized into aldehyde, that is subsequently oxidised, they are all reducing sugars. Ketones attached to glycosides, on the other hand, are nonreducing sugars.
  • Ketones lack a carbonyl group at the end of the chain, resulting in a hemiketal cyclic ring structure, as opposed to the hemiacetal ring structure found in aldehydes.
  • In ketoses, the carbon atoms are asymmetrical, resulting in various sugar forms due to the chirality of the asymmetrical carbon. The position of the hydroxyl group on the carbon backbone distinguishes the L- as well as D- types of ketoses.
  • Seliwanoff’s test can distinguish ketoses from aldoses. The test is predicated on a faster dehydration reaction in ketosis, that results in a faster test result.

Aldose Vs Ketose: Definition, Differences, Examples

Key Differences between Aldose and Ketose

(Aldose Vs Ketose)

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Aldose examples


  • Glucose is an aldose monosaccharide sugar with the chemical formula C6H12O6 that is produced largely by photosynthesis in plants as well as algae.
  • Since glucose can be used by a wide range of organisms, it is the most significant source of energy for many of them.
  • It can also be stored as a polymer in plants, such as starch, as well as in animals, such as glycogen. During metabolism, the polymers are broken down into glucose units.
  • D-glucose is the naturally occurring type of glucose, whereas L-glucose can be synthesised for specialised use.
  • D-glucose is more significant than L-glucose since biological systems have D-glucose use pathways.
  • Glucose has six carbon atoms as well as an aldehyde group, making it an aldohexose. The glucose molecule can be found in two forms: open-chain (acyclic) as well as ring (cyclic).

Ketose examples


  • Fructose, along with glucose as well as galactose, is a simple hexose sugar present in plants as well as is one of the three dietary monosaccharides.
  • Fructose has a ketone functional group, as well as fructose’s ring structure forms at the second carbon position. Fructose has a 5-carbon ring structure with an intramolecular hemiacetal structure.
  • It’s the most water-soluble of all the sugars, as well as it forms a sucrose-like disaccharide structure with glucose.
  • High-fructose corn syrup is made with glucose monosaccharides taken from plant sources such as sugar cane, maize, as well as beets.
  • Internal hydrogen-bonding stabilises the hemiketal structure of fructose, resulting in the crystalline form. D-fructopyranose is the crystalline form.



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