Fructose

In glucose, the aldehyde group at the C-1 atom reacts with the hydroxyl group at C-5 to form a
ring. This ring form is also called a pyranose because it resembles pyran.
By forming this ring an asymmetrical carbon atom on carbon atom 1 is formed. Because of
this, two different forms of the sugar are possible. These two forms are called alpha or beta-D-
Glucopyranose.
Ketose also form a ring structure. The keto group at C-2 reacts with the hydroxyl group at C-5 and
form a ring structure. This five carbon atom ring is called a furanose because it resembles furan.
Glucose
Glucose is also called dextrose. Glucose is a sugar that consists of six carbon
atoms. These carbon atoms lie in a ring. This gives an asymmetrical molecule
of five carbon atoms in a ring and 1 carbon atom outside of the ring.
Glucose is generally present in living organisms. The human blood contains
approximately 0.8 g/l (5 mmol/l) of glucose. In case of an illness, the glucose
level may have changed. Glucose is also a many measured mark in hospital
laboratories.
Glucose is taken up in the small intestine and is transported to the liver via the hepatic portal
vein. The liver regulates the glucose concentrations in the blood. If there is too much glucose in
the blood, glycogen is formed. And when there is too little glucose in the blood, this glycogen is
broken down again into glucose. This is all regulated in the glycogen metabolism.
Glucose is used as a fuel, glucose is energy. The use of glucose as energy happens in the metabolic
processes: Glycolysis and Citric acid cycle.
Fructose
Fructose, is found in high concentrations in fruits and is a constituent of
honey. Fructose tastes less sweet than glucose. Fructose is a sugar that
exists of six carbon atoms. These carbon atoms lie in one ring. This gives a
symmetric molecule of four carbon atoms in one ring and two carbon atoms
at both sides of the ring.
Fructose is not taken up as well as glucose by the small intestine.
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