5 questions on "Metabolic Pathway of Microorganisms - Nitrogen Fixation"

What is the difference between free-living and symbiotic nitrogen-fixing bacteria?
Free-living nitrogen-fixing bacteria carry out the process independently and symbiotic nitrogen-fixing bacteria only fix nitrogen in association with certain plants.
What is a heterocyst?
A differentiated cell that protects nitrogenase from O2, because nitrogen fixation is inhibited by oxygen because dinitrogenase reductase is irreversibly inactived by O2.
What is the sequence of electron transfer in nitrogenase?
Electron donor --> dinitrogenase reductase --> dinitrogenase --> N2.
How many electrons are needed for the reduction of N2 to ammonia and why? What else is needed for nitrogen fixation?
8 electrons are needed, because N2 has a triple bond and H2 is lost in the process. 16 ATP is needed, which binds to dinitrogenase reductase that lowers the reduction potential of the protein.
Which other triply bonded compounds does nitrogenases reduce and what is it used for?
Acetylene is reduced to ethylene. It's used for a technique, called acetylene reduction assay, to detect nitrogen fixation.
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