Glucose

Glucose, a simple monosaccharide sugar, is one of the most important carbohydrates and is used as a source of energy in animals and plants. Glucose is one of the main products of photosynthesis and starts respiration. The natural form (D-glucose) is also referred to as dextrose, especially in the food industry.

Isomerism

There are two enantiomers (mirror-image isomers) of the sugar, D-glucose and L-glucose, but in living organisms, only the D-isomer is found. Whether a carbohydrate is D or L has to do with the isomeric conformation of the hydroxyl on carbon 5. If it is to the right in the Fischer projection, then the ring form will be the D enantiomer, if it is to the left, it will be the L enantiomer. This is easy to remember, as the D is for "dextro," which is a Latin root for "right," where as L is for "levo" which comes from the Latin root for "left." The ring structure itself may form in two additionally different ways, yielding α (alpha) glucose and β (beta) glucose. Structurally, they differ in the orientation of the hydroxyl group linked to the first carbon in the ring. The α form has the hydroxyl group "below" the hydrogen (as the molecule is conventionally drawn, as in the figure above), while the β form has the hydroxyl group "above" the hydrogen.

Related Topics:
Enantiomer - Isomers - Fischer projection - Latin

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These two forms interconvert over a timescale of hours in aqueous solution, to a final stable ratio of α:β 36:64, in a process called mutarotation. This process can be speeded up.

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D-Glucose has the same configuration at its penultimate carbon as D-glyceraldehyde.

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