Pentose

The pentoses are Monosaccharide S which comprise 5 Atome S of Carbone.

They have a whole a grouping carbonyl:

  • either a function Aldehyde in position 1 (aldopentoses)
  • or a function Ketone in position 2 (mainly), 3, or 4 (cétopentoses).

The aldopentoses have 3 centers of chirality (" carbon asymétrique" atoms;); there are thus 4 Stéréoisomère S different possible.

The 4 D-aldopentoses are: -

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

The cétopentoses have 2 chiral centers and thus 4 stéréoisomères possible - Ribulose, Arabulose, Xylulose and Lyxulose.

The functional groupings aldehyde and ketone of these carbohydrates react with the functional groupings Hydroxyle to form groupings Hémiacétal Intramoléculaire S or Hémicétal S, respectively. The resulting cyclic structure is connected with the Furane S, and is called Furanose. The cycle opens and is closed spontaneously, thus making rotation possible around the connection between the grouping carbonyl and the atom close to carbon - thus providing two distinct configurations (α and β). This process is called Mutarotation.

Ribose is constituent ARN, the Désoxyribose is constituent DNA.

See too

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