Glucose is a source of energy. It is a carbohydrate molecule. Glucose, also called dextrose, one of a group of carbohydrates known as simple sugars (monosaccharides), is a simple sugar with the molecular formula C6H12O6, which means that it is a molecule that is made of six carbon atoms, twelve hydrogen atoms, and six oxygen atoms. Glucose circulates in the blood of animals as blood sugar.