Glucose is a six-carbon sugar molecule which is highly polar and easily dissolves in water. This hexose molecule can be found in L and D conformations, but our body only recognizes D-glucose.
Glucose is the main energy source for body cells. When cells take glucose from the bloodstream, the sugar molecule is broken down through the process of glycolysis, which converts the hexose into pyruvate. Pyruvate can be metabolized further in the citric acid cycle.
According to Essentials of Glycobiology, glucose plays a structural role with its inclusion in carbohydrate additions to proteins. These carbohydrate groups play important roles involving enzyme functions and binding.
Although most body cells can utilize fats for energy in a pinch, brain cells and red blood cells rely almost completely on glucose to fulfill their energy needs. Even short periods of glucose shortages can kill these types of cells.
Our bodies can adapt to a wide range of dietary carbohydrate intake, but Human Anatomy and Physiology states that the general recommendation is 125 to 175 grams per day. A majority of this amount should be complex carbohydrates (grains and vegetables) as opposed to simple sugars such as candy.