pentosi

Pentosi, in many languages including Italian, refers to pentose sugars, a class of monosaccharides characterized by five carbon atoms in their carbon skeleton. They can exist as aldopentoses, containing an aldehyde group at carbon 1, or as ketopentoses, containing a ketone group at carbon 2. Like other sugars, they occur in enantiomeric forms (D- and L-), with biological systems typically preferring the D- configuration.

Common examples include aldopentoses such as ribose and deoxyribose (the latter lacking a hydroxyl group at the 2′ position), and arabinose; ketopentoses include ribulose and xylulose. Ribose is a key component of RNA, while deoxyribose is a fundamental part of DNA. Many other pentoses occur as constituents of plant polysaccharides, notably xylose in xylans and arabinose in arabinans, as well as in pectins and hemicelluloses. Pentoses can also be found in free form in small amounts in some foods and organisms.

Metabolism of pentoses is central to the pentose phosphate pathway (PPP), a metabolic route that generates NADPH and ribose-5-phosphate for nucleotide synthesis. The oxidative phase produces NADPH and ribulose-5-phosphate, while the non-oxidative phase interconverts various pentose phosphates to glycolytic intermediates such as glyceraldehyde-3-phosphate and fructose-6-phosphate. This pathway is important for reductive biosynthesis and for maintaining redox balance in cells, and deficiencies in its enzymes can lead to metabolic disorders.

Pentoses are also relevant industrially and nutritionally, arising from the breakdown of plant cell walls and serving as precursors in fermentation and bioconversion processes.