noun, plural: pentoses
A five-carbon monosaccharide
Monosaccharides are the simplest form of carbohydrates. They are classified according to the number of carbon atoms in a monosaccharide. In particular, a pentose is a monosaccharide with five carbon atoms. Monosaccharides may also be classified based on the type of carbonyl group they contain. An aldose is a monosaccharide that contains an aldehyde group (-CHO) at position 1 whereas a ketose is one that contains a ketone (C=O) at position 2 or 3. Thus, an aldopentose is a pentose with an aldehyde group. A ketopentose, in contrast, is a pentose with a ketone functional group located in position 2 or 3.
Examples of aldopentoses are ribose, arabinose, lyxose, and xylose. Ribose (chemical formula C5H10O5) and deoxy-ribose are constituents of nucleotides and nucleic acids. In particular, ribose is the pentose sugar component of the nucleotides of RNA whereas deoxyribose is the sugar component of the nucleotides of DNA. Arabinose is also naturally occurring. For example, it is a component of hemicellulose and pectin. Lyxose occurs naturally as well but relatively less common in nature. For example, it can be found as a component of bacterial glycolipids. Xylose is first isolated from wood. It is the main component of the hemicellulose xylan.
Examples of ketopentoses are ribulose and xylulose.
Word origin: pent(a)- ("five") + -ose (relating to sugars)