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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 · 2025 · Paper I

Q7(a). T and R forms of haemoglobin

Question

Distinguish the ‘T’ (tense) and ‘R’ (relax) conformations of Hemoglobin on reversible binding of oxygen (O₂).

Answer in brief

T is the low-affinity deoxy form (high-spin Fe²⁺ out of the porphyrin plane, salt bridges intact); R is the high-affinity oxy form (low-spin iron in the plane, salt bridges broken).

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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 →

Covershaemoglobin T and R statescooperative oxygen bindingoxygen dissociation curveBohr effectspin state of ironmyoglobin

All parts of Question 7