- Tetroses are simple monosaccharides that contain four carbon atoms, with the general chemical formula C₄H₈O₄. They are classified according to the nature of their carbonyl group into aldotetroses, which contain an aldehyde group at carbon 1, and ketotetroses, which contain a ketone group typically at carbon 2. Despite their small size, tetroses are important in biochemistry because they serve as intermediates in metabolic pathways and provide insight into carbohydrate structure, stereochemistry, and function.
- Among the aldotetroses, the two common forms are D-erythrose and D-threose, both of which are stereoisomers differing in the spatial arrangement of the hydroxyl group at carbon 2. Erythrose, in particular, plays a key role in the pentose phosphate pathway and the Calvin cycle of photosynthesis in plants. It acts as a precursor for the synthesis of larger carbohydrates and certain aromatic amino acids such as phenylalanine, tyrosine, and tryptophan, via the shikimate pathway. Threose, while less common in mainstream metabolism, has become important in research contexts, such as the development of L-threose nucleic acid (TNA), an artificial genetic polymer studied as a potential precursor to RNA in theories of the origin of life.
- The ketotetroses include erythrulose, which has a ketone group at the second carbon. Erythrulose is noteworthy for its application in the cosmetic industry as an active ingredient in self-tanning products, often used alongside dihydroxyacetone (DHA). Like DHA, erythrulose reacts with amino acids in the outer layer of the skin through the Maillard reaction, forming brown-colored polymers that simulate a natural tan. Erythrulose is preferred in some formulations because it produces a slower, more even browning effect compared to DHA, reducing the risk of streaking.
- In the context of biological chemistry, tetroses are not typically stored or transported in large amounts but function mainly as short-lived intermediates in metabolic networks. Their reactivity makes them crucial connectors between simple sugars like trioses and more complex carbohydrates such as pentoses and hexoses. This intermediate position reflects their potential role in both modern biochemistry and prebiotic chemistry. Some studies suggest that tetroses could have been involved in early chemical pathways leading to the emergence of RNA or DNA precursors, highlighting their significance in the study of life’s origins.
- From a structural standpoint, tetroses provide important examples for understanding carbohydrate stereochemistry. Aldotetroses, with two chiral centers, can exist in four stereoisomeric forms (D- and L-erythrose, D- and L-threose), while ketotetroses, with only one chiral center, have two stereoisomers. These stereochemical relationships make tetroses useful in teaching and research for illustrating the rules of chirality, Fischer projections, and D/L nomenclature in carbohydrate chemistry.
