Lecture 15 Flashcards
What do we do with the nitrogen we inhale?
We simply exhale it because we have no enzymes to convert it in to a usable form
What are the 4 ways to fixate nitrogen?
- Lightning: converts N2 -> NH4+
- Waste/dead organisms can be converted into NH4+ by microbial decomposers. NH4+ then gets converted into NO2- by denitrifying bacteria, which then gets converted into NO3-. It can then undergo nitrification (like in legumes) or denitrification (back to N2 in air)
- Haber-Bosch process (artificial) of making N2 -> NH3
- Denitrifying bacteria can return nitrogen back to the air (NO3- -> N2)
What are bacteria who can fix N2 called?
Diazotrophs
How much energy must be applied to break a N2 triple bond?
930 kJ/mol
Compare conditions necessary to fixate ammonia in Haber-Bosch process versus biological nitrogen fixation
Haber-Bosch requires 400-500°C and several hundred atm of pressure.
Biological nitrogen fixation occurs at ambient temp and pressure.
Which 2 steps in N2 fixation/conversion involve energy release?
NH3 -> NO2- -> NO3-
Which form of nitrogen is used to synthesize organic nitrogen compounds, such as amino acids?
NH3
What is the chemical equation for biological nitrogen reduction via nitrogenase?
N2 + (10H+) + 8e- + 16ATP + (2NH4H+) + 16ADP + 16Pi +H2
Name the subunits of the nitrogenase complex
Beta, alpha, and reductase subunits
How is it that nitrogen fixation (N2 + 3H2 -> 2NH3) is an exergonic reaction despite N2’s strong triple bond?
In part by LOTS of ATP hydrolysis. Need 16 ATPs.
Describe the process of electron transfer in the nitrogenase complex
ATP binds the first reductase subunit, which then transfers to the 4Fe-S redox center in the reductase. This gets passed along to the P-cluster in the dinitrogenase subunit (the ATP induced a conformational change to bring the 4Fe-S center closer to the P-cluster). The P-cluster then transfers electrons to the FeMo cofactor.
Eventualy 8 electrons accumulate
How many ATP bind per round of turn of the nitrogenase complex cycle?
2 because there are 2 reductase subunits
What inactivates the nitrogenase complex? How have bacteria solved this problem?
Oxygen. Bacteria who live in leguminous root nodules are bathed in leghemoglobin, which binds oxygen so that it doesn’t interfere with nitrogen fixation
What are the 2 different reductases?
Nitrate and nitrite
Which enzyme is responsible for providing a safe entry point for ammonia? In which organisms is it found?
Glutamine synthetase. Found in all organisms.
