Question
Explain the overall biochemical stepwise reduction of nitrogen to ammonia biological nitrogen fixation. Include the summary chemical reaction equation.
Answers
GPT-4o mini
Biological nitrogen fixation is a crucial process through which atmospheric nitrogen (\(N_2\)) is converted into ammonia (\(NH_3\), which can then be used by organisms to synthesize essential compounds such as amino acids, nucleotides, and other nitrogen-containing molecules. This transformation requires an input of energy and is primarily performed by certain bacteria and archaea, notably those belonging to the genera *Rhizobium*, *Azotobacter*, and *Frankia*, as well as by symbiotic organisms associated with legumes.
### Stepwise Reduction of Nitrogen to Ammonia
1. **Nitrogenase Enzyme Complex**: The nitrogen fixation process begins with the nitrogenase enzyme complex, which consists of two main components: the dinitrogenase (or MoFe-protein) and the dinitrogenase reductase (or Fe-protein). This complex catalyzes the conversion of nitrogen gas to ammonia.
2. **Electron Transfer**: The dinitrogenase reductase (Fe-protein) is responsible for transferring electrons to the dinitrogenase (MoFe-protein). This transfer requires energy, which is supplied by ATP hydrolysis. Each cycle of ATP hydrolysis provides the necessary energy for the enzyme complex to function.
3. **Binding of Nitrogen**: Once reduced ferredoxin or flavodoxin donates electrons to the nitrogenase, nitrogen gas (\(N_2\)) binds to the active site of MoFe-protein. The bound nitrogen is activated for reduction.
4. **Reduction of Nitrogen**: A series of electron transfer and protonation steps occur, where \(N_2\) is sequentially reduced to hydrazine (\(N_2H_4\)), and later to ammonia (\(NH_3\)). Protonation typically occurs at specific stages of the reduction process, transforming bound intermediates until ammonia is produced.
5. **Release of Ammonia**: Once \(NH_3\) formation is complete, it is released from the enzyme complex, enabling the nitrogenase to accept another molecule of nitrogen for further reduction.
### Overall Chemical Reaction
The overall biochemical reaction for biological nitrogen fixation can be summarized as follows:
\[
N_2 (g) + 8 H^+ + 8 e^- + 16 ATP \rightarrow 2 NH_3 (aq) + H_2 (g) + 16 ADP + 16 P_i
\]
This equation reflects that atmospheric nitrogen is reduced to ammonia through multiple steps involving protons and electrons, powered by ATP. The by-product \(H_2\) is generally released during the process, and the ATP is hydrolyzed to ADP and inorganic phosphate (\(P_i\)).
### Key Points
- The nitrogenase complex is critical for the nitrogen fixation process.
- Biological nitrogen fixation requires significant energy input from ATP.
- Various microorganisms are capable of fixing nitrogen, primarily under anaerobic conditions to protect nitrogenase from oxygen.
- The resultant ammonia can be assimilated by plants and other organisms, thereby integrating nitrogen from the atmosphere into the biological cycle.
### Stepwise Reduction of Nitrogen to Ammonia
1. **Nitrogenase Enzyme Complex**: The nitrogen fixation process begins with the nitrogenase enzyme complex, which consists of two main components: the dinitrogenase (or MoFe-protein) and the dinitrogenase reductase (or Fe-protein). This complex catalyzes the conversion of nitrogen gas to ammonia.
2. **Electron Transfer**: The dinitrogenase reductase (Fe-protein) is responsible for transferring electrons to the dinitrogenase (MoFe-protein). This transfer requires energy, which is supplied by ATP hydrolysis. Each cycle of ATP hydrolysis provides the necessary energy for the enzyme complex to function.
3. **Binding of Nitrogen**: Once reduced ferredoxin or flavodoxin donates electrons to the nitrogenase, nitrogen gas (\(N_2\)) binds to the active site of MoFe-protein. The bound nitrogen is activated for reduction.
4. **Reduction of Nitrogen**: A series of electron transfer and protonation steps occur, where \(N_2\) is sequentially reduced to hydrazine (\(N_2H_4\)), and later to ammonia (\(NH_3\)). Protonation typically occurs at specific stages of the reduction process, transforming bound intermediates until ammonia is produced.
5. **Release of Ammonia**: Once \(NH_3\) formation is complete, it is released from the enzyme complex, enabling the nitrogenase to accept another molecule of nitrogen for further reduction.
### Overall Chemical Reaction
The overall biochemical reaction for biological nitrogen fixation can be summarized as follows:
\[
N_2 (g) + 8 H^+ + 8 e^- + 16 ATP \rightarrow 2 NH_3 (aq) + H_2 (g) + 16 ADP + 16 P_i
\]
This equation reflects that atmospheric nitrogen is reduced to ammonia through multiple steps involving protons and electrons, powered by ATP. The by-product \(H_2\) is generally released during the process, and the ATP is hydrolyzed to ADP and inorganic phosphate (\(P_i\)).
### Key Points
- The nitrogenase complex is critical for the nitrogen fixation process.
- Biological nitrogen fixation requires significant energy input from ATP.
- Various microorganisms are capable of fixing nitrogen, primarily under anaerobic conditions to protect nitrogenase from oxygen.
- The resultant ammonia can be assimilated by plants and other organisms, thereby integrating nitrogen from the atmosphere into the biological cycle.