Nitrogen cycle reactions

B a reaction in the nitrogen cycle C the carbon cycle D photoionization... 

The cytochromes are another group of haem proteins found in all aerobic forms of life. Cytochromes are electron carriers involving a Fe(ii)/Fe(m) redox system. They are a crucial part of the electron transfer reactions in mitochondria, in aspects of the nitrogen cycle, and in enzymic processes associated with photosynthesis. 

The nitrogen cycle is the complex series of reactions by which nitrogen is slowly but continually recycled in the atmosphere, lithosphere (earth) and hydrosphere (water). Atmospheric nitrogen is made accessible to us and other life-forms in mainly two ways. 

In denitrification, part of the biological nitrogen cycle, nitrate in the soil is converted via four enzymatic reactions stepwise to nitrite, nitric oxide and nitrous oxide to finally yield gaseous nitrogen. 

The involvement of HA during bacterial conversion of nitrate to NH3 (known also as the nitrate ammonification phase of the nitrogen cycle) has been studied at the molecular level as part of an effort to delineate the mechanism of conversion of nitrite to NH3 by a group of multiheme cytochromes of bacterial origin. The overall reduction reaction is depicted in equation 3 for cytochrome c-nitrite reductase " ... 

Summary of the major reactions of the nitrogen cycle. From Sprent (1987). 

There has been a great deal of research on the combustion of small hydrocarbons, including nitrogen-cycle chemistry leading to nitric-oxide formation and abatement [138]. There are a number of methane-air reaction mechanisms that have been developed and validated [274,276,278], the most popular one being GRI-Mech [366]. There is also active research on the kinetics of large hydrocarbon combustion [81,88,171,246,328-330,426]. 

What chemical reactions are included in these two important components of the nitrogen cycle (see also Fig. 24-1) ... 

The Nitrogen Cycle Encompasses a Series of Reactions in Which Nitrogen Passes through Many Forms... 

Nitrogen cycle. The passage of nitrogen through various valence states, as the result of reactions carried out by a wide variety of different organisms. 

Finally, human impact on the nitrogen cycle can affect the structure and intensity of biospheric energy exchange. As can be seen in Table 4.7, there are possibilities of considerable shifts in such an exchange depending on intensification of one or another reaction. 

The 14N atom is the fourth mostabundantnucleus that is produced by nucleosynthesis in the stars (after l60,12C and 20Ne). Its nucleosynthesis occurs primarily in stars of insufficient mass to become supernovae, especially in AGB stars (see Glossary). It is the natural byproduct of the fusion of hydrogen into helium in the carbon-nitrogen cycle. The 14N is created by proton-capture reactions transmuting the initial C and O within the star to 14N during the CN cycle. Production from intial C and O makes 14N a secondary nucleus, since it can be made only in proportion to the amount of C... 

Nitrogen is returned to its atmospheric form by the action of denitrifying bacteria such as Pseudomonas thiobacillus and Micrococcus denitriflcans. The process is referred to as denitrification and represents the major mechanism of nitrogen loss in the overall nitrogen cycle whereby various forms of nitrogen in the soil revert to the N2 form. The reactions and their energetics are given below ... 

A class of enzymes found in bacteria within root nodules in some plants, which catalyze reactions by which N2 molecules from the air are converted to ammonia. For more information see Enzymes Nitrogen Cycle... 

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