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UPSC Civil Services (Mains)

Chemistry optional

  • 2 papers
  • 250 marks each
  • 3 h per paper
  • 5 of 8 questions, Q1 and Q5 compulsory

Paper I covers physical and inorganic chemistry.

UPSC Civil Services (Mains), Chemistry optional · 2021 · Paper I

Q7(a). Iron–sulphur proteins: structures and redox states

Question

Draw the structures of various iron-sulphur proteins and their corresponding redox states.

Answer in brief

There are four kinds of site, all with tetrahedral, high-spin iron held by sulphur: rubredoxin Fe(S–Cys)₄ and the 2Fe–2S, 3Fe–4S and 4Fe–4S clusters, each carrying one electron at a time.

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The full model answer

As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.

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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 →

Coversiron-sulphur proteinsferredoxinrubredoxinHiPIP4Fe-4S clusterbioinorganic electron transfer

All parts of Question 7