Nitrogen Cycle
Content
NITROGEN CYCLE
• Nitrogen Fixation is the process that causes the strong twoatom nitrogen molecules found in the atmosphere to break apart so they can combine with other atoms • Nitrogen gets fixed when it is combined with oxygen or hydrogen. • The enormous energy of lightning breaks nitrogen molecules apart and enables the nitrogen atoms to combine with oxygen forming nitrogen oxides (N2O). Nitrogen oxides dissolve in rain, forming nitrates. Nitrates (NO3) are carried to the ground with the rain. • Industrial Fixation • Biological fixation
• The term nitrification refers to the conversion of ammonium to nitrate . • This is brought about by the nitrifying bacteria, which are specialised to gain their energy by oxidising ammonium, while using CO2 as their source of carbon to synthesise organic compounds. • Chemoautotrophs • They are found as mixed-species communities (termed consortia) • Nitrosomonas species - convert ammonium to nitrite (NO2-) • Nitrobacterspecies - convert nitrite to nitrate (NO3-). • Most plants and microorganisms can take up either nitrate or ammonium.
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Nitrifying bacteria convert toxic ammonia to less harmful nitrate. Nitrosomonas sp. Bacteria oxidize ammonia into nitrite Nitrobacter bacteria convert nitrite to nitrate Ammonia can be used by some plants. Most nitrogen taken up by plants is converted by chemoautotrophic bacteria from ammonia, which is highly toxic to many organisms, first into nitrite (NO2-), and then into nitrate (NO3-). This process is called nitrification, and these bacteria are known as nitrifying bacteria
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It aids in the decomposition of nitrogenous material and thus in the recycling of nitrogen atoms since the decontamination of organic nitrogen produces ammonia that is subsequently oxidized to nitrate by nitrification.
Denitrification
• Nitrate is converted to gaseous compounds (nitric oxide, nitrous oxide and N2) by microorganisms. • The sequence usually involves the production of nitrite (NO2-) as an intermediate step. • Several types of bacteria perform this conversion when growing on organic matter in anaerobic conditions. Because of the lack of oxygen for normal aerobic respiration, they use nitrate in place of oxygen. • Common denitrifying bacteria include several species of Pseudomonas, Alkaligenes and Bacillus. • This results in substantial losses of nitrogen into the atmosphere, roughly balancing the amount of nitrogen fixation that occurs each year.
NITROGENASE • Nitrogenase enzyme catalyses the reduction of N2 to NH3 accompanied by reduction of protons to H
• N-N triple bond : breaking of all three chemical bonds. • Requires rather large inputs of energy Released from the hydrolysis of ATP, to overcome the activation energy barrier. • • Nitrogenase consists of two major protein components • The enzyme is composed of the heterotetrameric MoFe protein that is transiently associated with the homodimeric Fe protein.
dinitrogenase (MoFe-protein) and dinitrogenase reductase (Fe-protein). The iron (Fe) and molybdenum (Mo) in dinitrogenase (MoFe-protein) are contained in a cofactor called MoFe-cofactor.
• The nitrogenase proteins are denatured by exposure to oxygen due to its oxidative properties
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Nitrogenase Reductase (NR) is an iron-containing protein that accepts electrons from ferredoxin, a strong reductant, and then delivers them to the other component, called Nitrogenase, or IronMolybdenum protein. • Nitrogenase first accepts electrons from NR and protons from solution. • Nitrogenase binds a molecule of molecular nitrogen and then accepts electrons and protons from NR, adding them to the N2 molecule, eventually releasing two molecules of ammonia, NH3.
• Nitrogen-fixing systems contain hydrogenase, which harvests the electrons from molecular hydrogen and transfers them back to ferredoxin, thus saving some of the metabolic energy that is lost during nitrogen reduction.
• Root nodules of nitrogen-fixing plants contain an oxygen-binding protein, leghemoglobin, which protects nitrogenase by binding molecular oxygen.
• Nitrogen Fixation is the process that causes the strong twoatom nitrogen molecules found in the atmosphere to break apart so they can combine with other atoms • Nitrogen gets fixed when it is combined with oxygen or hydrogen. • The enormous energy of lightning breaks nitrogen molecules apart and enables the nitrogen atoms to combine with oxygen forming nitrogen oxides (N2O). Nitrogen oxides dissolve in rain, forming nitrates. Nitrates (NO3) are carried to the ground with the rain. • Industrial Fixation • Biological fixation
• The term nitrification refers to the conversion of ammonium to nitrate . • This is brought about by the nitrifying bacteria, which are specialised to gain their energy by oxidising ammonium, while using CO2 as their source of carbon to synthesise organic compounds. • Chemoautotrophs • They are found as mixed-species communities (termed consortia) • Nitrosomonas species - convert ammonium to nitrite (NO2-) • Nitrobacterspecies - convert nitrite to nitrate (NO3-). • Most plants and microorganisms can take up either nitrate or ammonium.
• • • • •
Nitrifying bacteria convert toxic ammonia to less harmful nitrate. Nitrosomonas sp. Bacteria oxidize ammonia into nitrite Nitrobacter bacteria convert nitrite to nitrate Ammonia can be used by some plants. Most nitrogen taken up by plants is converted by chemoautotrophic bacteria from ammonia, which is highly toxic to many organisms, first into nitrite (NO2-), and then into nitrate (NO3-). This process is called nitrification, and these bacteria are known as nitrifying bacteria
•
•
It aids in the decomposition of nitrogenous material and thus in the recycling of nitrogen atoms since the decontamination of organic nitrogen produces ammonia that is subsequently oxidized to nitrate by nitrification.
Denitrification
• Nitrate is converted to gaseous compounds (nitric oxide, nitrous oxide and N2) by microorganisms. • The sequence usually involves the production of nitrite (NO2-) as an intermediate step. • Several types of bacteria perform this conversion when growing on organic matter in anaerobic conditions. Because of the lack of oxygen for normal aerobic respiration, they use nitrate in place of oxygen. • Common denitrifying bacteria include several species of Pseudomonas, Alkaligenes and Bacillus. • This results in substantial losses of nitrogen into the atmosphere, roughly balancing the amount of nitrogen fixation that occurs each year.
NITROGENASE • Nitrogenase enzyme catalyses the reduction of N2 to NH3 accompanied by reduction of protons to H
• N-N triple bond : breaking of all three chemical bonds. • Requires rather large inputs of energy Released from the hydrolysis of ATP, to overcome the activation energy barrier. • • Nitrogenase consists of two major protein components • The enzyme is composed of the heterotetrameric MoFe protein that is transiently associated with the homodimeric Fe protein.
dinitrogenase (MoFe-protein) and dinitrogenase reductase (Fe-protein). The iron (Fe) and molybdenum (Mo) in dinitrogenase (MoFe-protein) are contained in a cofactor called MoFe-cofactor.
• The nitrogenase proteins are denatured by exposure to oxygen due to its oxidative properties
•
Nitrogenase Reductase (NR) is an iron-containing protein that accepts electrons from ferredoxin, a strong reductant, and then delivers them to the other component, called Nitrogenase, or IronMolybdenum protein. • Nitrogenase first accepts electrons from NR and protons from solution. • Nitrogenase binds a molecule of molecular nitrogen and then accepts electrons and protons from NR, adding them to the N2 molecule, eventually releasing two molecules of ammonia, NH3.
• Nitrogen-fixing systems contain hydrogenase, which harvests the electrons from molecular hydrogen and transfers them back to ferredoxin, thus saving some of the metabolic energy that is lost during nitrogen reduction.
• Root nodules of nitrogen-fixing plants contain an oxygen-binding protein, leghemoglobin, which protects nitrogenase by binding molecular oxygen.
