Pentose


Pentose

A pentose is a monosaccharide with five carbon atoms.

They either have an aldehyde functional group in position 1 (aldopentoses), or a ketone functional group in position 2 (ketopentoses).

The aldopentoses have three chiral centres ("asymmetric carbon atoms") and so 8 different stereoisomers are possible.

The 4 D-aldopentoses are:

CH=O CH=O CH=O CH=O
| |
HC-OH HO-CH HC-OH HO-CH
| |
HC-OH HC-OH HO-CH HO-CH
| |
HC-OH HC-OH HC-OH HC-OH
| |
CH2OH CH2OH CH2OH CH2OH D-Ribose D-Arabinose D-Xylose D-Lyxose

The ketopentoses have 2 chiral centres and therefore 4 possible stereoisomers — ribulose (L- and D-form) and xylulose (L- and D-form).

The D-isomers of both are known to occur naturally as is the L-isomer of xylulose: CH2OH CH2OH
| C=O C=O
| HC-OH HO-CH
| HC-OH HC-OH
| CH2OH CH2OH D-Ribulose D-Xylulose

The aldehyde and ketone functional groups in these carbohydrates react with neighbouring hydroxyl functional groups to form intramolecular hemiacetals or hemiketals, respectively. The resulting ring structure is related to furan, and is termed a furanose. The ring spontaneously opens and closes, allowing rotation to occur about the bond between the carbonyl group and the neighbouring carbon atom — yielding two distinct configurations (α and β). This process is termed mutarotation.

Ribose is a constituent of RNA, and the related deoxyribose of DNA.

A polymer composed of pentose sugars is called a pentosan.

See also

* Triose
* Tetrose
* Hexose
* Heptose
* Pentose phosphate pathway


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Look at other dictionaries:

  • pentose — [ pɛ̃toz ] n. m. • 1890; de pent et 1. ose ♦ Biochim. Ose à cinq atomes de carbone. Le ribose est un pentose. ● pentose nom masculin Nom générique des oses C5H10O5, dérivant du pentane. (Les seuls pentoses importants sont les aldopentoses,… …   Encyclopédie Universelle

  • Pentose — Pen tose, n. [Penta + ose.] (Chem.) Any of a group of sugars of the formula {C5H10O5}, such as as {arabinose} or {ribose}; so called from the five carbon atoms in the molecule. They are not fermented by yeast. [Webster 1913 Suppl.] …   The Collaborative International Dictionary of English

  • pentose — s. f. [Química] Açúcar simples que contém cinco átomos de carbono.   ‣ Etimologia: penta + ose …   Dicionário da Língua Portuguesa

  • pentose — [pen′tōs΄] n. [ PENT(A) + OSE1] any of a group of monosaccharides, C5H10O5, including ribose and arabinose …   English World dictionary

  • Pentose — Les pentoses sont des oses (monosaccharides) qui comportent 5 atomes de carbone. Ils ont tous la même formule brute C5H10O5. Ils possèdent tous un groupement carbonyle : soit une fonction aldéhyde en position 1 (aldopentoses) soit une… …   Wikipédia en Français

  • pentose — noun A sugar or saccharide containing five carbon atoms. Ribose, found in RNA, is a common pentose …   Wiktionary

  • pentose — pentozė statusas T sritis chemija apibrėžtis Monosacharidas, kurio pagrindinėje grandinėje yra penki C atomai. atitikmenys: angl. pentose rus. пентоза …   Chemijos terminų aiškinamasis žodynas

  • pentose — noun Etymology: International Scientific Vocabulary Date: 1890 a monosaccharide C5H10O5 (as ribose) that contains five carbon atoms in the molecule …   New Collegiate Dictionary

  • Pentose — Pentosen (von griech. pente fünf) sind Monosaccharide, deren Kohlenstoffgrundgerüst fünf Kohlenstoff Atome enthält. Sie haben alle die Summenformel C5H10O5 und unterscheiden sich durch die Art der Carbonyl Funktion. Handelt es sich um eine Keton… …   Deutsch Wikipedia

  • pentose — /pen tohs/, n. Chem. a monosaccharide containing five atoms of carbon, as xylose, C5H10O5, or produced from pentosans by hydrolysis. [ < G (1890); see PENT , OSE2] * * * …   Universalium


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