pentosas

Pentosas, or pentoses, are monosaccharides containing five carbon atoms. They can exist as linear aldehyde forms (aldopentoses) or ketone forms (ketopentoses) and most commonly adopt five-membered cyclic structures called furanoses in solution. In biology, the naturally occurring forms are typically the D-operons of these sugars, with L-forms present only in limited contexts.

Common aldopentoses include ribose, xylose, arabinose, and erythrose, while ketopentoses include ribulose and xylulose. A notable derivative is deoxyribose, a deoxyaldopentose that lacks one hydroxyl group at C2 and is a structural component of DNA.

Biological roles are diverse. Ribose is a key component of RNA and is part of several cofactors such as ATP and NADX; deoxyribose is essential for DNA structure. Ribose-5-phosphate, produced in the pentose phosphate pathway, serves as a precursor for nucleotide synthesis and contributes to cellular NADPH production for reductive biosynthesis and redox balance. Erythrose-4-phosphate is an intermediate in the shikimate pathway, leading to aromatic amino acids in plants and microbes. Xylose and arabinose occur in plant cell walls and are metabolized by certain microorganisms; they are also used industrially in the production of xylitol and other derivatives.

Metabolic interconversion is possible: the non-oxidative branch of the pentose phosphate pathway and related rearrangements allow pentoses to be converted to glycolytic intermediates, linking nucleotide synthesis with energy metabolism.