What is the chemical equation for carbohydrates

carbohydrates (also obsolete carbohydrates) or Saccharides form the large natural product class of hydroxyaldehydes or hydroxyketones as well as compounds derived therefrom and their oligo- and polycondensates. In general, carbohydrates are understood as sugar. Carbohydrates, together with fats and proteins, make up the quantitatively largest usable (including starch) and non-usable (fiber) portion of food. In addition to their central role as a physiological energy carrier, they play an important role as a supporting substance, especially in the plant kingdom and in biological signaling and recognition processes (e.g. cell-cell recognition, blood groups). Their non-condensed representatives, the monosaccharides, have carbon chains with at least three carbon atoms and at least one center of chirality (exception: dihydroxyacetone). The most common are monosaccharides with five or six carbon atoms. Two and multiple sugars consist of single sugars linked by glycosidic bonds. The monosaccharides (simple sugars, e.g. grape sugar, fructose), disaccharides (double sugars, e.g. granulated sugar, lactose, malt sugar) and oligosaccharides (multiple sugars, e.g. raffinose) are usually water-soluble, have a sweet taste and are called sugar in the narrower sense. The polysaccharides (polysaccharides, e.g. starch, cellulose, chitin), on the other hand, are often poorly or not at all soluble in water and have a neutral taste.


Since many prominent saccharides have the gross formula Cn(H2O)m these can be seen formally as hydrates of carbon, which is why K. Schmidt coined the term carbohydrates, which is still used today, in 1844. Representatives of this substance class can, however, deviate considerably from this gross formula and contain further functional groups and also heteroatoms such as nitrogen or sulfur, while other compounds of the same formula do not belong to the carbohydrates, as they are not hydroxyaldehydes or hydroxyketones. In general, carbohydrates are present when at least one aldehyde group or keto group and at least two hydroxyl groups can be found in a substance. Since polysaccharides are made up of monosaccharides, the formula applies nC.6H12O6 -> C6nH10n + 2O5n + 1 + n-1(H2O)

Physiological synthesis

Simple sugars are built up by plants in the Calvin cycle through photosynthesis from carbon dioxide and water, and contain carbon, hydrogen and oxygen. In practically all living beings, these simple sugars are then linked to form multiple sugars for storage or for cell construction. For example, the liver synthesizes the long-chain storage sugar glycogen from glucose.

The energy supply of the brain is highly dependent on glucose, since it cannot directly use fats for energy. In starvation situations without carbohydrate intake or with increased muscle work, glucose is therefore synthesized in gluconeogenesis from the metabolic products lactate, certain amino acids (including alanine) and glycerine. Gluconeogenesis uses some enzymes from glycolysis, the breakdown pathway of glucose for the production of high-energy ATP and NADH + H+, but is by no means to be understood as the reverse of this, since decisive steps of own enzymes take place under energy consumption, as I said. Glycolysis and gluconeogenesis are reciprocally regulated; H. they close one another in one and the same cell nearly out. Different organs can, however, go one way and the other at the same time. For example, when there is strong muscle activity, glycolysis and thus lactate release takes place in the muscle and gluconeogenesis using lactate in the liver. This shifts part of the metabolic load to the liver.


Carbohydrates are an essential part of the human diet alongside fat and protein. They are the main source of energy for the organism and, in contrast to fats, can be used quickly, but are not considered essential, as the body can produce them in gluconeogenesis using energy from other food components. Since the brain in particular is highly dependent on glucose as an energy source and cannot utilize fats, the blood sugar level must be kept within narrow limits. Its regulation takes place through the interaction of insulin and glucagon. When there is a lack of carbohydrates, the brain is supplied by ketone bodies, which z. B. noticeable during a diet by the acetone odor. A completely carbohydrate-free diet was easily tolerated in animal experiments with chickens [1]. An independent disease in humans due to the lack of carbohydrates is unknown. [2]The energy content of one gram of carbohydrate is around 17.2 kilojoules (kJ) (4.1 kcal).

The physiological energy production from carbohydrates normally takes place in the non-oxidative glycolysis and in the oxidative citrate cycle.

In the short term, glucose is stored as glycogen in the liver and muscle tissue. If the supply of carbohydrates to the tissues is greater than their consumption, the excess is converted into fat and stored as depot fat.

Examples of foods high in carbohydrates: bread, pasta, beans, potatoes, bran, rice, and cereals.

Plant species that mainly contribute to the intake of carbohydrates in the diet are listed in the article Crop Plants.


According to their function in the organism, carbohydrates can be divided into structural carbohydrates and non-structural carbohydrates:

  • Non-structural carbohydrates include cane sugar (sucrose) and the polysaccharide starch. These sugars are used to generate energy or are storage materials.
  • Structural carbohydrates are involved in the construction of the plant cell wall and represent a large part of the fiber material in plants: cellulose, hemicellulose, and others.

Structural carbohydrates can only be digested to a limited extent by mammals with a single-cavity stomach, but largely or completely by ruminants (Ruminantia), camel-like (Camelidae) (these are also ruminants, but not in the systematic sense, as ruminants developed independently) and equine species (Equidae).

The classification according to chemical structure is shown in the section "List of carbohydrates".

List of important carbohydrates

  • Simple sugars (monosaccharides)
  • Double sugar (disaccharides)
    • Sucrose, also beet sugar or cane sugar (glucose + fructose)
    • Lactose, also milk sugar (glucose + galactose)
    • Lactulose, a synthetically modified milk sugar
    • Maltose, also malt sugar (glucose + glucose)
    • Trehalose
  • Triple sugar (trisaccharide)
  • Polysaccharides
  • Cyclodextrins: cyclic oligosaccharides with a chiral cavity
    • α-cyclodextrin (ring of six glucose units)
    • β-cyclodextrin (seven glucose units)
    • γ-cyclodextrin (eight glucose units)


Carbohydrates are hydroxy aldehydes or hydroxy ketones and compounds derived therefrom, so in their open-chain form they have at least one aldehyde group or keto group in addition to at least two hydroxyl groups. If it is a hydroxyaldehyde (carbonyl group on a terminal carbon atom (aldehyde)), it is called an aldose, if it is a hydroxyketone (carbonyl group on an internal carbon atom (ketone)), then the name is sugar than ketosis. The carbonyl function is a highly reactive functional group: The easy oxidizability to carboxylic acid, reduction to alcohol and the easy nucleophilic attack on the carbon atom of the carbonyl group should be mentioned here.

  • Carbohydrates are oxidized to aldonic acids by oxidizing agents. Under basic conditions, this applies not only to the aldoses, but also to the ketoses, which are rearranged by the base in a complex reaction (the aldose form occurring in the course of the keto-enol tautomerism is stabilized). When detected by the Fehling's reagent, a blue Cu (II) tartaric acid complex is reduced to insoluble, red Cu (I) oxide.
  • If the carbonyl function is reduced to a hydroxyl group, a so-called alditol is obtained.
  • Intramolecular nucleophilic attack by one of the hydroxyl groups on the carbonyl carbon atom forms a cyclic hemiacetal, which is usually very favorable in terms of energy. Here, predominantly six-membered rings (pyranose shape) are formed, which have a very low ring tension, but five-membered rings (furanose shape) are also formed to a lesser extent. Other ring sizes do not occur because they have too high a ring tension. A new center of chirality is also created. The two resulting diastereomers are referred to as α and β. In aqueous solution, the α- and β-pyranose and -furanose forms form an equilibrium reaction with one another and with the open-chain form. An aqueous solution of pure α-glucopyranose therefore turns into an equilibrium mixture of α- and β-glucopyranose and -furanose (38% α-Glcp, 62% β-Glcp, 0% α-Glcf, 0.14% β -Glcf, 0.002% open-chain). The measurable change in the rotation value is called mutarotation.
(*) While aliphatic aldehydes are gradually oxidized to carboxylic acid by atmospheric oxygen, carbohydrates are considerably less sensitive due to the formation of acetals, which is undoubtedly of enormous importance for such an important class of biomolecules.
  • Of central importance in carbohydrate chemistry is also glycosidic bond. The cyclic full acetal of a sugar formed here is referred to as Glycoside.
  • The open-chain aldehyde of the carbohydrate reacts reversibly with amines (e.g. in amino acids, proteins) via an imine to form Amadori productwhich in turn can also condense with amine (acid) s and rearrange itself irreversibly:
R-NH2 + OHC-CH (OH) -R ' R-N = CH-CH (OH) -R´ (Imine) R-NH-CH2-C (O) -R´ (Amadori product) Rearrangement products
This non-enzymatic reaction with amino acids and proteins takes place relatively frequently in the organism and is one of the central processes in aging (e.g. age spots), as the reaction products cannot be broken down by the body. It also plays an important role in the thermal preparation of foods, e.g. B. frying and cooking. The typical browning occurs because conjugated ring systems are formed that are colored. These products of the so-called Maillard reaction are also decisive for the taste of prepared foods.

Chemists who helped research into carbohydrates


  1. * Renner R, Elcombe AM. Metabolic effects of feeding "carbohydrate-free" diets to chicks. J Nutr 1967; 93: 31-6
  2. * http: //www.ajcn.org/cgi/content/full/75/5/951-a


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Categories: Carbohydrate | Substance group