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NEET 2020 · BiologyPrevious Year Question

The specific palindromic sequence which is recognized by EcoRI is

Answer: (C) 5' - GAATTC - 3' / 3' - CTTAAG - 5'. Answer: (C) 5' - GAATTC - 3' / 3' - CTTAAG - 5' Solution: EcoRI recognises the palindromic hexamer that reads 5'-GAATTC-3' on the top strand with its complement 3'-CTTAAG-5' on the bottom strand; the sequence reads the same in 5'→3' on both strands, satisfying the palindrome rule.

  1. A.5' - CTTAAG - 3' / 3' - GAATTC - 5'
  2. B.5' - GGATCC - 3' / 3' - CCTAGG - 5'
  3. C.5' - GAATTC - 3' / 3' - CTTAAG - 5'✓
  4. D.5' - GGAACC - 3' / 3' - CCTTGG - 5'

Correct Answer

(C) 5' - GAATTC - 3' / 3' - CTTAAG - 5'

Solution & Explanation

Answer: (C) 5' - GAATTC - 3' / 3' - CTTAAG - 5' Solution: EcoRI recognises the palindromic hexamer that reads 5'-GAATTC-3' on the top strand with its complement 3'-CTTAAG-5' on the bottom strand; the sequence reads the same in 5'→3' on both strands, satisfying the palindrome rule. Option A reverses the strand assignment, B is the BamHI site (GGATCC), and D (GGAACC/CCTTGG) is not a palindrome. This is answer_source=external (NEET 2020) but is NCERT-derived directly from the worked palindrome example. NCERT Reference: Ch 9, p.167, line(s) 6-7 — "5' —— GAATTC —— 3'"

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