einsykrur

Einsykrur, or monosaccharides, are the simplest class of carbohydrates. The term derives from the Icelandic words eins meaning "one" and sykur meaning "sugar." They cannot be hydrolyzed into smaller carbohydrate units and are typically aldehydes or ketones with multiple hydroxyl groups. Most monosaccharides contain between three and seven carbon atoms and are classified as triose, tetrose, pentose, or hexose; common examples include glyceraldehyde (triose), ribose and deoxyribose (pentoses), and glucose, galactose, and fructose (hexoses). In solution, many monosaccharides exist in cyclic form as α- or β-anomers, via hemiacetal or hemiketal linkages forming furanose or pyranose rings.

They are highly water-soluble, generally sweet, and many act as reducing sugars. They serve as essential energy sources and metabolic intermediates. Hexoses such as glucose provide immediate energy through glycolysis, while ribose and deoxyribose are key components of nucleic acids. Monosaccharides are also fundamental building blocks for disaccharides and polysaccharides, and they contribute to glycoproteins and glycolipids.

Biologically, monosaccharides originate mainly from photosynthesis in plants and are released during digestion from starch and sucrose. In cells, they are often phosphorylated to trap them and feed into pathways such as glycolysis and the pentose phosphate pathway. The properties of a monosaccharide—carbon count, functional group position, and stereochemistry—determine its reactivity and biological role.