Fructose is a chemical component of table sugar. Sucrose, the chemical name for table sugar, is a large molecule made up of a fructose molecule chemically bonded to a glucose molecule. Both fructose and glucose are monosaccharides, which means single sugar unit. Bonded together in the form of sucrose, they form a disaccharide, which means double sugar unit. Since fructose tastes quite a bit sweeter than glucose, when they're combined in the form of sucrose, the combination has a sweetness between that of glucose and fructose.

Natural Fructose

Pure fructose isn't common in nature -- most of the fructose you consume from natural sources is chemically combined with glucose in the form of sucrose. Fruit does contain some pure fructose, however. Through the process of photosynthesis, plants make both glucose and fructose. Some of these monosaccharides, the plant leaves unmodified in pure form -- this is the source of pure fructose in fruit. It's possible, but not particularly practical, to isolate pure fructose from fruit.