The monosaccharides are carbohydrates consisting of a single chain polihidroxialdehídica (aldose) or polihidroxicetónica (ketoses). They cannot be decomposed by hydrolysis. They are named by adding the ending -ose to the number of carbons, such as triose, tetrose, pentose, hexose, etc.
- An aldose is a monosaccharide whose molecule contains an aldehyde group, that is, a carbonyl at the end of it. The simplest aldose is glyceraldehyde, which has only three carbon atoms.
A ketose is a monosaccharide with one ketone group per molecule. The dihydroxyacetone, three carbon atoms, is the simplest and only ketose having no optical activity.
Therefore, aldoses and ketoses have a carbonyl group (carbon double bonded to oxygen).
- Physical properties They are crystalline solids, white in color, sweet-tasting, and soluble in water, since hydroxyl radicals (-OH) and hydrogen radicals (-H) establish hydrogen bonds with water molecules.
- Chemical properties. The presence of the carbonyl group also gives them reducing properties that, as will be seen later, are used to identify them.
Monosaccharides can be oxidized (or they reduce) by certain ions such as the ferric ion (Fe3+) and cupric (Cu2+) that will pass when reduced to Fe2+ or Cu+1.The carbonyl group of monosaccharides becomes acidic when it is oxidized.
This is the basis of the Fehling reaction in which a blue solution, due to the presence of Cu2+, becomes Cu+, red in color, in the presence of reducing sugars such as glucose.
Another chemical property of carbohydrates is their ability to associate with -NH2 amino groups.