Fructose, glucose and sucrose

Fructose, glucose, and sucrose are different types of sugars or carbohydrates. The fructose is a simple six – carbon sugar with a ketone group on the second carbon; the glucose is a simple six – carbon sugar but with an aldehyde group on the first carbon. The sucrose is a disaccharide, ie comprises both glucose and fructose monosaccharides.

These three sugars are made up of carbon, hydrogen and oxygen, so they are organic compounds. The functional chemical groups that characterize carbohydrates are the hydroxyl group (-OH) and the carbonyl group (-C = O).

DefinitionSix-carbon ketohexose monosaccharide.Aldohexose six-carbon monosaccharide.Disaccharide formed by the union of fructose and glucose.
Number of carbons6 carbons6 carbons12 carbons
Functional groupCetona y poly


Aldehyde and poly-




Chemical formulaC6H12O6C6H12O6C12H22O11
Where to getFruits, honey.Fruits, as part of starches in vegetables.Common table sugar, extracted from sugar cane or beets.

What is fructose?

Fructose is a simple sugar or monosaccharide, with the formula C 6 H 12 O 6 . The word “fructose” derives from the Latin fructus which means “fruit”. Therefore, the greatest source of fructose is found in fruits.

Fructose chemical structure

The fructose molecule is characterized by having a carbonyl group on the second carbon of a chain of six, which is why it is described as a ketone and hexose or ketohexose .

Monosaccharides that have six carbons tend to form a cyclic structure, in this case the hydroxyl of carbon 5 reacts with carbon 2 of the ketone group, forming a five-sided ring or cyclopentane. Since fructose cyclopentane resembles the compound furan, it is also called fructofuranose 

Fructose metabolism

Fructose is absorbed in the small intestine and passes into the portal vein. In the liver, all fructose is taken up and transformed into fructose-1-phosphate by the enzyme fructokinase. Fructose-1-phosphate can then enter the glycolytic pathway. The metabolism of fructose does not require the participation of the hormone insulin.

When there is an excess of fructose in the intake, especially from the consumption of sweetened beverages, it can also be transformed into triglycerides, so the consumption of fructose is associated with fatty liver.

Fructose sources

Fructose represents one third of the sugars found in honey. However, the fructose in honey is primarily in the form of a six-sided ring or pyranose. This fructopyranose is much sweeter than fructofuranose.

Fruits are an important source of fructose but we also get it as part of the sucrose molecule, the common sugar in kitchens. Corn syrup used as a sweetener in the food industry is made up of fructose.

What is glucose?

Glucose is the most abundant carbohydrate on Earth. It is a simple sugar or monosaccharide, with the formula C 6 H 12 O 6 , just like fructose, so both monosaccharides are isomers of each other.

Glucose is the monosaccharide component of the storage polysaccharides: starch (in plants) and glycogen (in animals). It is also a constituent part of the structural polysaccharide of plant cell walls (cellulose). Plants produce glucose through the process of photosynthesis , from carbon dioxide, water, and solar energy.

Glucose is also the source of energy for most heterotrophic organisms, through the process of glycolysis .

In humans, glucose is stored in the liver and muscles as glycogen. On the other hand, when we talk about blood sugar, we are referring to the amount of glucose that circulates in the blood.

Chemical structure of glucose

Glucose is characterized by having a carbonyl group on the first carbon of a chain of six, which is why it is described as an aldehyde and hexose or aldohexose . It also has five hydroxyl groups (-OH) so it is also identified as a polyol.

As it has six carbons, it tends to form a cyclic structure by reacting the hydroxyl of carbon 5 with carbon 1 of the carbonyl group, forming a six-sided ring or cyclohexane. Since glucose cyclohexane resembles the pyran compound, it is also called glucopyranose .Glucose metabolism

Glucose in plants and animals has three metabolic pathways:

  1. Storage.
  2. Glycolysis to obtain ATP.
  3. Oxidation via pentoses to obtain biosynthetic precursors.

Glucose is absorbed into intestinal cells by membrane transporters and rapidly passes into the bloodstream. Glucose metabolism in humans is regulated by the pancreatic hormones insulin and glucagon.

Chronic excess glucose in the blood is what we know as diabetes .

Glucose sources

The main source of glucose comes from starches in vegetables. Starches are linked glucose chains; In the digestive system there are enzymes that are responsible for releasing these glucose that are absorbed in the small intestine.

Free glucose is also found in fruits and glucose is part of the lactose molecule, which is the sugar in milk.

What is sucrose?

Sucrose is a disaccharide of formula C 12 H 22 O 11 , formed by the union between glucose and fructose. It is what we commonly know as table sugar, which is extracted mainly from sugar cane or beets.

It is formed only in plants, and it is the compound that plants use to transport excess sugar precursors from the leaves to the other parts of the leaves.

Sucrose chemical structure

Sucrose has a glycosidic bond that forms between carbon 1 of glucose and the hydroxyl oxygen on carbon 2 of fructose. It is denoted as glucopyranosyl (ɑ 1 → 2ß) fructofuranose.Sucrose metabolism

Sucrose in the digestive system is separated into glucose and fructose by the action of the enzyme sucrase-isomaltase, each of the sugars being absorbed by the intestinal cells.

Sucrose sources

Sucrose is the form of transport of carbohydrates in plants to storage organs, where it is transformed into starch.

The table sugar that we use on a daily basis is extracted mainly from sugar cane and eggplant.

Glucose, fructose and sucrose content in food

Here is a table with the values ​​of the glucose, fructose and sucrose content of different foods (in percent of solids):

Sugar content by percentage of solids
Sweet corn2213
Sweet potato, sweet potato2115

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