What are Sugars (concept and chemical classification)

The sugars They are the simplest way to carbohydrates. They are made up of oxygen atoms (EITHER)carbon (C) and hydrogen (H) and comply with the chemical formula CnH2nOn. They are also called simple monosaccharides.

In nature, there are different types of sugars depending on their chemical structure. The best known are the glucose and the fructosebut the variety is wide and includes the lactose (found in milk), among others.

He table sugarcall saccharosecontains glucose and fructose.

On the left, we see table sugar, which contains glucose and fructose; On the right, we find milk, which contains lactose.

The sugars are important because they are the base or the skeleton of the carbohydrates more complex.

Chemical classification of sugars

The chemical classification of sugars depends on three factors:

According to location of the oxygen atom in the molecule. According to the amount of carbon which has the central structure. According to the orientation of the molecules of hydroxyl (-OH) of the penultimate carbon with respect to the central chain.

Example of the factors considered when classifying a sugar.

The three factors used to classify sugars using D-lyxose as an example.

Before explaining the classification according to these three factors in more detail, let’s look at an example with glucose.

The enantiomers of glucose.

The glucose is a aldose because it has an aldehyde group in it C1.The glucose is a hexose because it has 6 carbons.The D-glucose have the C5 oriented to the rightthe L-glucose have the C5 oriented toward the left.

Now we will explain in more detail how this classification is arrived at.

Depending on the location of the oxygen atom in the molecule

Considering the location of the atom oxygen With respect to carbon number 1 (C1) in the molecule, we find:

Pads: contain a group aldehyde in carbon C1. That is, a carbon associated with a double bond oxygen (=O)a single-bonded hydrogen (-H) and another single bond carbon (-C).
Ketoses: contain a group ketone in carbon C2. That is, a carbon associated with a double bond oxygen (=O)and two other single-bonded carbons (-C).

Let’s look at the example with glucose and fructose:

Classification of sugars according to the functional group from which they are derived. On the left, an aldose (derived from the aldehyde), on the right, a ketose (derived from the ketone).

The glucose has the double bond oxygen on carbon #1 (C1)while the fructose has the double bond oxygen on carbon #2 (C2).

Depending on the amount of carbon in the central structure

In function of the amount of carbon that it contains in the central structure, we can identify the following sugars:

Sugars derived from aldehyde or aldoseaccording to amount of carbonare the following:

3 carbons: glyceraldehyde.
4 carbons: erythrose and threose.
5 carbons: ribose, arabinose (included in the diet of diabetics), xylose (used in diagnostic tests) and lyxose (found in some bacteria).
6 carbons: allose, altrose, glucose, mannose (present in the white blood cell membrane), gulose, idose, galactose (precursor to breast milk) and thallose.

Sugars derived from ketone or ketosesaccording to amount of carbonare the following:

3 carbons: dihydroxyacetone (present in cane sugar).

Cane sugar contains dihydroxyacetone.

4 carbons: erythrulose (present in strawberries).

Strawberries contain erythrulose.

5 carbons: ribulose (involved in carbon fixation in plants) and xylulose.
6 carbons: psychose, fructose (present in honey), sorbose and tagatose (sweetener).

Honey has fructose.

Depending on the orientation of the hydroxyl molecules of the penultimate carbon

Taking into account the orientation of the group hydroxyl (-OH) of the penultimate carbon, sugars could be subdivided as follows:

D- or dextro-rotary: when the hydroxyl (-OH) of the penultimate carbon (C) is located towards the right.
L- or levo-rotary: when the hydroxyl (-OH) of the penultimate carbon (C) is located towards the left.

Molecules with orientation d and l They are known as isomers. Sugars contain a mixture of both isomers but in living beings It is normal to find the D shape of sugars.

For more information you can read Carbohydrates.

How to cite: Jesús, Sara (06/04/2019). “What are Sugars (concept and chemical classification).” In: Meanings.com. Available in: https:///azucares/ Consulted:

Pharmacist from the Central University of Venezuela (2009), with a mention in Applied Microbiology. Currently, he is pursuing postgraduate studies in Cell Biology.