Nonhexoses

Nonhexoses refer to carbohydrates that are not hexoses, meaning they are not monosaccharides composed of six carbon atoms. Hexoses, such as glucose and fructose, are the most common simple sugars, but nonhexoses encompass a broader range of sugar structures with varying carbon chain lengths and functional groups.

The simplest nonhexoses are pentoses, which contain five carbon atoms. Ribose and deoxyribose are notable pentoses found in RNA and DNA, respectively, where they form the backbone of nucleic acids. Other pentoses, like arabinose and xylose, are commonly found in plant cell walls and hemicellulose.

Tetroses, with four carbon atoms, are less common but include erythrose and threose, which play roles in metabolic pathways like the pentose phosphate pathway. Ketotetroses, such as erythrulose, are also found in nature, though they are less studied.

Heptoses, containing seven carbon atoms, are rare but include sedoheptulose, which participates in the Calvin cycle of photosynthesis. Similarly, octoses and larger sugars are uncommon but can be found in specialized biological roles.

Nonhexoses also include modified sugars, such as deoxy sugars (e.g., 2-deoxyribose) and amino sugars (e.g., glucosamine and galactosamine), which incorporate nitrogen or lack oxygen atoms. These derivatives are crucial in glycoproteins, glycolipids, and bacterial cell walls.

While hexoses dominate as energy sources and structural components, nonhexoses contribute to genetic material, metabolic regulation, and complex biomolecular structures. Their diversity reflects the adaptability of carbohydrates in biological systems.