Types

• Aldohexose sugars have six carbons and an aldehyde group, which is an OH group attached to a terminal carbon, at one end of the chain. There are 16 possible stereoisomers of an aldohexose sugar, two of which are called glucose.
  
  

Function

• One of the glucose stereoisomers is an enantiomer of the other. An enantiomer has a mirror-image structure that cannot be superimposed on the other enantiomer, rather in the same way your right hand is a mirror image of your left but the two cannot be superimposed--a right hand won't fit into a left-hand glove. The two glucose enantiomers are called L-glucose and D-glucose.
  
  

Considerations

• Only D-glucose is biologically active; your cells cannot use L-glucose in the same way they would D-glucose. D-glucose is sometimes called dextrose, especially in the food industry. D-glucose can adopt either a six-membered ring configuration or a chain shape. In solution, most glucose exists in the six-membered ring configuration.