Glucose is a simple sugar that serves as the main source of energy for the body. The carbohydrates we eat are broken down into glucose (and a few other simple sugars), absorbed by the small intestine and circulated throughout the body.
Glucose, with six carbon atoms, has four asymmetric carbon atoms. The arrangement of the OH's and H's on these atoms is very important. Structural formulas for sugar molecules are often written in the vertical arrangement with the aldehyde or the ketone group at or near the top.