Zinc is an essential trace element. Which of the following biochemical functions is directly dependent on zinc as a structural or catalytic cofactor?

• A RNA polymerase activity via zinc fingers (Cys2His2) that stabilise transcription factor binding to DNA ✓
• B Synthesis of thyroxine (T4) from tyrosine in thyroid follicular cells
• C Haem synthesis at the step of ferrochelatase incorporating Fe²⁺ into protoporphyrin IX
• D Conversion of homocysteine to methionine via methionine synthase

Explanation

Zinc is an essential catalytic and structural cofactor in over 300 enzymes. In the context of transcription factors, zinc finger motifs (typically Cys2His2 or Cys4 coordination geometries) use zinc to maintain a stable domain structure enabling DNA binding (e.g., Sp1, glucocorticoid receptors, p53). Zinc also catalyses activity in carbonic anhydrase, carboxypeptidase, alcohol dehydrogenase, and Cu/Zn-SOD. Thyroxine synthesis requires iodine and thyroid peroxidase (which uses heme iron). Ferrochelatase incorporates Fe²⁺ and requires pyridoxal phosphate, not zinc. Methionine synthase requires vitamin B12 (cobalamin).

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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