Indian Forest Service (Mains), Chemistry optional · 2024 · Paper I

Q5(e). Why biological nitrogen fixation needs an enzyme

8 marks
Topic: Bio-inorganic chemistry
Answered

Question

Write the chemical equation for nitrogen fixation by nitrogenase. Discuss the thermodynamic and kinetic aspects of N₂ reduction and explain why it requires an enzyme.

Answer in brief

The minimum conventional stoichiometry is N₂ + 8H⁺ + 8e⁻ + 16ATP → 2NH₃ + H₂ + 16ADP + 16Pᵢ.

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Topic notes: bio-inorganic chemistry (haemoglobin, cytochromes, Fe–S proteins, ion pumps), with every Civil Services, IFoS and Geo-Scientist PYQ →

Coversnitrogenasebiological nitrogen fixationFeMo cofactorATP hydrolysisN≡N bond activation

All parts of Question 5

5(a) Solubility of alkali-metal halides8 marks
5(b) Isomers of a cobalt A₂B₂C₂ complex8 marks
5(c) Dicobalt octacarbonyl and infrared bands8 marks
5(d) Relativity and lanthanide contraction8 marks
5(e) Why biological nitrogen fixation needs an enzyme8 marks