They are white substances with a sweet taste, crystallizable and soluble in water. They are easily oxidized, turning into acids, which is why they are said to have reducing power (when oxidized, they are reduced to another molecule). These are the monomers of the rest of the carbohydrates, which means that all the others are formed by polymerization (binding) of these.
It can be said that monosaccharides are simple molecules that correspond to the general formula (CH2O) n. They are made up of 3, 4, 5, 6 or 7 carbon atoms. Chemically they are polyalcohols, that is, carbon chains with one -OH group on each carbon, in which one carbon forms an aldehyde group or a ketone group.
Monosaccharides are studied by two ways of representing their molecule.
- Fisher's linear formula.
- Haworth's cyclical formula.
The Fisher formula represents molecule monosaccharide in a linear manner, which does not correspond to reality, no longer it serves to explain many chemical reactions, however, several authors used to explain some of its properties.
Haworth's formula is currently recognized as real, that is, when the monosaccharide is in disuse. This formula is cyclical, which makes the molecules take the form of geometric figures, pentagons, hexagons, etc.
We must not forget that monosaccharides are polyalcohols that have an aldehyde or ketone group.
Monosaccharides are classified according to the number of carbon atoms and according to the position of the carbonyl group in the molecule. According to the number of carbon atoms, they are divided into:
- Trioses (3 carbon atoms).
- Tetrose (4 carbon atoms).
- Pentose (5 carbon atoms).
- Hexose (6 carbon atoms).
- Heptosa (7 carbon atoms).
These sugars constitute the monomeric units of carbohydrates to form polysaccharides. All individual monosaccharides have one or more asymmetric carbons, minus dihydroxyacetone. The simplest case, that of glyceraldehyde, has a center of asymmetry, which gives rise to two possible conformations: D and L isomers.
When the carbonyl group is at the end of the molecule, the monosaccharide will be an aldose. When the carbonyl group is not at the end, but in an intermediate position, the monosaccharide will be ketosis.
