Carbon fixation

With carbon dioxide assimilation ( assimilation of Latin assimulatio Ähnlichmachung ) is called in animals the uptake of carbon and oxygen from carbon dioxide ( CO2) for the synthesis of organic, endogenous carbon compounds. The first step is the formation of a carboxyl group. Since carbon dioxide is thereby bound to the organic matter, it is also called carbon fixation.

We distinguish autotrophic and heterotrophic carbon dioxide assimilation. In autotrophic creatures carbon dioxide is the only carbon source for building the body's own building materials. Contrast Heterotrophic beings mainly use organic carbon compounds as a building material source and assimilate carbon dioxide, only a small proportion.

Since life on Earth is based on the chemical diversity of carbon compounds, that is, all living things need carbon for their cell components and metabolism, is the ability of autotrophs, namely plants, many bacteria and archaea, organic carbon compounds exclusively from inorganic substances to synthesize, the condition for the existence of heterotrophic life forms that are dependent on the availability of organic matter.

There are various ways in which carbon dioxide is assimilated. In the following two ways autotrophs occur:

• Calvin cycle ( alternative names: Calvin - Benson - Bassham cycle, reductive pentose phosphate cycle, dark reaction of photosynthesis )
• Reductive citric acid cycle ( alternative name: Arnon - Buchanan cycle)
• Reductive acetyl -CoA pathway ( alternative names: Wood - Ljungdahl pathway, CO-Dehydrogenase/Acetyl-CoA-Synthase-Weg )
• 3- Hydroxypropionatzyklus ( alternative name: 3-Hydroxypropionat/Malyl-CoA-Zyklus )
• 3-Hydroxypropionat/4-Hydroxybutyratzyklus
• Dicarboxylat/4-Hydroxybutyratzyklus
• ( Serine pathway )
• ( Ethylmalonyl -CoA pathway)

While plants and cyanobacteria use only the Calvin cycle, the other to find ways at different representatives in the kingdom of bacteria and archaea, which are thus able to grow with carbon dioxide as the sole carbon source ( autotrophic ).

Heterotrophs with carbon dioxide is introduced for some anaplerotic reactions in the metabolism, for example, in the formation of oxaloacetate from pyruvate and carbon dioxide.