noun, plural: nonoses
Monosaccharides are the simplest form of carbohydrates. They are classified according to the number of carbon atoms in a monosaccharide. In particular, a nonose is a monosaccharide with nine 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. Thus, an aldononose would be a nonose with an aldehyde group. A ketononose, in contrast, would be a nonose with a ketone functional group.
Examples of nonoses are neuraminic acid, sialic acid, legionaminic acid, and psudaminic acid.Neuraminic acid [IUPAC name: (4S,5R,6R,7S,8R)-5-amino-4,6,7,8,9-pentahydroxy-2-oxo-nonanoic acid] is a nonose with a chemical formula of C9H17NO8. It does not occur naturally. Nevertheless, its derivatives are commonly found in bacteria and animal tissues. For instance, sialic acid refers to any of the N- or O- substituted derivatives of neuraminic acid. The sialic acids are widely distributed in animal tissues and occur as components of oligosaccharide chains of mucins.
Biosynthesis of sialic acid begins by the production of N-acetylglucosamine-6-P via the catalytic action of transferase on glucosamine-6-phosphate and acetyl-CoA. Through epimerization, it is converted to N-acetylmannosamine-6-P that reacts with PEP, resulting in the formation of N-acetylneuraminic-9-P (which is a sialic acid).
In bacteria, sialic acid biosynthesis is carried out by using a mannose derivative. The enzyme aldolase inserts three carbons (from pyruvate) to it, producing sialic acid structure.
Word origin: non(a)- ("nine") + -ose (relating to sugars)