monosaccharides

Monosaccharides are the simplest carbohydrates, consisting of a single sugar unit. They cannot be hydrolyzed into smaller carbohydrate components and serve as the fundamental building blocks for more complex carbohydrates. Most monosaccharides have the empirical formula (CH2O)n, with n typically between three and seven; common examples include triose, tetrose, pentose, hexose, and heptose sugars.

Chemically, monosaccharides contain multiple hydroxyl groups and a carbonyl group, which defines them as aldoses (aldehyde group) or ketoses (ketone group). They can exist in an open-chain form or in cyclic forms in solution, with five- and six-membered rings known as furanose and pyranose forms. In aqueous solution, cyclic forms predominate, and the ring can adopt alpha or beta configurations at the anomeric carbon.

Aldoses and ketoses are further differentiated by the position of the carbonyl group. Key hexoses include glucose and galactose (aldoses) and fructose (a ketose); common pentoses include ribose and deoxyribose, which are components of nucleic acids. Most biologically relevant monosaccharides occur in the D- configuration, with L- isomers largely absent in nature.

Biological roles of monosaccharides include providing immediate energy through pathways such as glycolysis, serving as carbon skeletons for nucleotide synthesis, and acting as monomeric units for disaccharides and polysaccharides. They can participate in redox reactions, be oxidized to sugar acids, or reduced to sugar alcohols. Monosaccharides are typically highly soluble in water and often have a sweet taste.