How is the structure of carbohydrates

carbohydratesBiomolecules The carbohydrates are among the most important natural substances. They are hydroxyaldehydes and ketones that react intramolecularly in solution and form rings. Well-known representatives are, for example, glucose (grape sugar), fructose (fruit sugar), lactose (milk sugar), sucrose (household sugar) as well as starches and celluloses. Carbohydrates play a central role in the storage and production of energy in all living things. In addition, they have numerous other functions in the organism, for example for the biosynthesis of metabolic products and molecular communication.

synonymous: sugar, carbohydrates, carbohydrates


Carbohydrates ("sugar") are found in many natural and processed foods, drugs, medical devices and dietary supplements.

Foods with carbohydrates include, for example, pasta, cereals, flour, dough, bread, legumes, potatoes, corn, honey, sweets, fruits, sweet drinks and dairy products.


Carbohydrates are natural substances and biomolecules that usually only consist of carbon (C), hydrogen (H) and oxygen (O) atoms. Other atoms can be included, for example nitrogen (N) in the amino sugars.

The name is derived from carbon and water and in fact the empirical formula of the monosaccharides can be expressed as follows: Cn (H2O) n. For example, the following applies to glucose: C6H12O6 = C6(H2O)6.

Carbohydrates have hydroxyl groups and they are aldehydes or ketones. They can be viewed as the oxidation products of polyhydric alcohols.

Depending on the number of carbon atoms, the simple sugars (→ monosaccharides) are designated as follows:

  • Trioses (3), e.g. glyceraldehyde
  • Tetroses (4), e.g. erythrosis
  • Pentoses (5), e.g. ribose, xylose
  • Hexoses (6), e.g. glucose, fructose

Glyceraldehyde is a triose and the simplest aldose:

Examples: aldoses

The following figure shows examples of aldoses:

Ring formation

Carbohydrates can react intramolecularly and form stable rings. These are known as hemiacetals and hemiketals. Rings with 5 links are called furanoses and with 6 links pyranoses. A distinction is made between aldoses (aldehydes) and ketoses (ketones). For example, fructose is a ketohexose and glucose is an aldohexose.


The carbohydrates typically have multiple chiral centers and a large number of stereoisomers. The prefixes D- (Dextro, right) and L- (Levo, left) have prevailed for the designation of the enantiomer pairs. They refer to the configuration of the carbon atom furthest from the carbonyl group (C = O). D-sugars occur frequently, but not exclusively, in nature.

Two diastereoisomers are possible in ring formation. The hydroxyl group can be oriented downwards (α-glucose) or upwards (β-glucose). One speaks of anomers and the anomeric carbon atom or center. The two ring shapes and the open-chain shape are in solution.


A bond creates the disaccharides (2), trisaccharides (3), oligosaccharides (3 to 10) and the polysaccharides, which consist of hundreds to many thousands of units, from individual simple sugars (monosaccharides).

One speaks of the glycosidic bond. Here, sugars with the α and β configuration can combine with one another at the anomeric center. Starches are in the α configuration, while celluloses are in the β configuration and are therefore indigestible for humans and are excreted as calorie-free fiber.

A distinction is also made as to which carbon atoms, respectively. Hydroxy groups are linked together. The glucose typically forms 1 → 4 and 1 → 6 bonds.

Polysaccharides and starch, click to enlarge. Illustration © PharmaWiki


The following list shows a small list of well-known representatives. There are numerous other carbohydrates.

Monosaccharides (Simple sugars):

Disaccharides (Double sugar, 2 units):

  • Lactose (milk sugar: glucose + galactose)
  • Maltose (malt sugar, glucose + glucose)
  • Sucrose (table sugar: glucose + fructose)

Trisaccharides (Triple sugar, 3 units):

  • Raffinose (galactose + glucose + fructose)

Oligosaccharides (3 to 10 units):

  • Maltodextrin (mixture of monomers, oligomers and polymers of glucose)

Polysaccharides are polymers (macromolecules) with hundreds to many thousands of carbohydrate units:


Carbohydrates are one of the most important groups of substances in nature. The most common organic molecules on earth are celluloses, which are polymers of glucose. Plants use carbon dioxide and water as substrates for synthesis and solar radiation as an energy source during photosynthesis.

Carbohydrates play a central role as energy stores (e.g. starch, glycogen), for energy production (ATP), for the synthesis of countless metabolic products, for signal transmission, for communication at the cellular and molecular level, for the synthesis of nucleic acids and they have many structural ones Functions.

application areas

In pharmacy and medicine (selection):


The nutrition societies recommend covering around 50% of your daily energy needs with carbohydrates.

unwanted effects

Carbohydrates are essential to life and should not be viewed as unhealthy. Excessive intake, for example in the form of sucrose, can lead to overweight and obesity. Many carbohydrates are cariogenic and can promote the development of tooth decay.

Some carbohydrates, such as indigestible oligosaccharides, can cause digestive disorders such as gas, abdominal pain and diarrhea, especially in sensitive people.

see also

Monosaccharides, disaccharides, polysaccharides

  • Medicinal product information (CH)
  • European Pharmacopoeia PhEur
  • Biochemistry books
  • Specialist literature
  • Organic chemistry textbooks
  • Encyclopedias of food technology
  • Pharmacotherapy Lexicons

Conflicts of Interest: None / Independent. The author has no relationships with the manufacturers and is not involved in the sale of the products mentioned.

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This article was last changed on 10/18/2020.
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