Nitrogénkötés

Nitrogénkötés, often translated as nitrogen fixation, is a vital biochemical process that converts atmospheric nitrogen gas (N2) into ammonia (NH3). Atmospheric nitrogen, which makes up about 78% of the Earth's atmosphere, is largely unavailable to most living organisms in its gaseous form because of the strong triple bond between the two nitrogen atoms. This bond requires a significant amount of energy to break.

Nitrogen fixation is primarily carried out by certain microorganisms, most notably bacteria. These bacteria can be free-living in the soil or water, or they can form symbiotic relationships with plants. The most well-known symbiotic relationship is between legumes, such as peas and beans, and Rhizobium bacteria. The bacteria reside in nodules on the plant's roots and receive carbohydrates from the plant in return for fixing nitrogen into a form the plant can utilize, such as ammonium ions.

There are two main types of biological nitrogen fixation: symbiotic and non-symbiotic. Symbiotic fixation, as described with legumes, is highly efficient. Non-symbiotic fixation occurs by free-living bacteria like Azotobacter. In addition to biological fixation, atmospheric nitrogen can also be fixed through abiotic processes, such as lightning, which provides the energy to convert nitrogen and oxygen into nitrogen oxides. Industrial processes, like the Haber-Bosch process, also fix nitrogen to produce ammonia for fertilizers, though this is not a natural phenomenon. The nitrogen fixed by these processes is essential for the synthesis of amino acids, proteins, nucleic acids (DNA and RNA), and other crucial organic molecules for life.