[ The two enantiomers of each pair generally have vastly different biological properties.
2-Ketohexoses are stable over a wide pH range, and with a primary p''K''a of 10.28, will only deprotonate at high pH, so are marginally less stable than aldohexoses in solution.
]
Natural occurrence and uses
The aldohexose that is most important in biochemistry is -glucose
Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...
, which is the main "fuel" for metabolism in many living organisms.
The 2-ketohexoses psicose
D-Psicose (C6H12O6), also known as D-allulose, or simply allulose, is a low-calorie epimer of the monosaccharide sugar fructose, used by some major commercial food and beverage manufacturers as a low-calorie sweetener. First identified in whea ...
, fructose and tagatose
Tagatose is a hexose monosaccharide. It is found in small quantities in a variety of foods, and has attracted attention as an alternative sweetener. It is often found in dairy products, because it is formed when milk is heated. It is similar in t ...
occur naturally as the -isomers, whereas sorbose
Sorbose is a ketose belonging to the group of sugars known as monosaccharides. It has a sweetness that is equivalent to sucrose (table sugar). The commercial production of vitamin C
Vitamin C (also known as ascorbic acid and ascorbate) ...
occurs naturally as the -isomer.
-Sorbose is commonly used in the commercial synthesis of ascorbic acid. -Tagatose is a rare natural ketohexose that is found in small quantities in food. - Fructose is responsible for the sweet taste of many fruits, and is a building block of sucrose, the common sugar.
Deoxyhexoses
The term "hexose" may sometimes be used to include the deoxyaldohexoses, which have one or more hydroxyl
In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydro ...
s (–OH) replaced by hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
atoms (–H). It is named as the parent hexose, with the prefix "''x''-deoxy-", the ''x'' indicating the carbon with the affected hydroxyl. Some examples of biological interest are
* -Fucose (6-deoxy--galactose)
* -Rhamnose (6-deoxy--mannose)
* -Quinovose (6-deoxy--glucose), found as part of the sulfolipid sulfoquinovosyl diacylglycerol (SQDG)
* -Pneumose (6-deoxy--talose)
See also
* Diose
A diose is a monosaccharide containing two carbon atoms. Because the general chemical formula of an unmodified monosaccharide is (C·H2O)''n'', where ''n'' is three or greater, it does not meet the formal definition of a monosaccharide. However, ...
* Triose
A triose is a monosaccharide, or simple sugar, containing three carbon atoms. There are only three possible trioses (including dihydroxyacetone): L-glyceraldehyde and D-glyceraldehyde, the two enantiomers of glyceraldehyde, which are aldotrios ...
* Tetrose A tetrose is a monosaccharide with 4 carbon atoms. They have either an aldehyde functional group in position 1 (aldotetroses) or a ketone functional group in position 2 (ketotetroses).
File:DErythrose Fischer.svg , D-Erythrose
File:DThreose Fisch ...
* Pentose
In chemistry, a pentose is a monosaccharide (simple sugar) with five carbon atoms. The chemical formula of many pentoses is , and their molecular weight is 150.13 g/mol.[Heptose
A heptose is a monosaccharide with seven carbon atoms.
They have either an aldehyde functional group in position 1 (aldoheptoses) or a ketone functional group in position 2, 3 or 4 (ketoheptoses). Ketoheptoses have 4 chiral centers, whereas ald ...]
* Octose An octose is a monosaccharide containing eight carbon atoms. Lincomycin contains the octose methylthiolincosamide.
See also
* Heptose
* Hexose
* Pentose
In chemistry, a pentose is a monosaccharide (simple sugar) with five carbon atoms. The c ...
References
External links
*
*
{{Carbohydrates
Monosaccharides