1
Which one of the following represents a palindromic sequence in DNA ?
- 5′-GAATTC-3′ 3′-CTTAAG-5′
- 5′-GATACC-3′ 3′-CCTAAG-5′
- 5′-CCAATG-3′ 3′-GAATCC-5′
- 5′-CATTAG-3′ 3′-GATAAC-5′
Answer
(1) 5′-GAATTC-3′ 3′-CTTAAG-5′
Solution
As per NCERT, a palindromic sequence in DNA is a base sequence that reads the same on the two strands when the orientation of reading is kept the same (both 5′ → 3′).
Option (1): upper strand 5′-GAATTC-3′; lower strand read 5′ → 3′ = 5′-GAATTC-3′ ⇒ same ⇒ palindrome (the EcoRI site).
Options (2), (3), (4): the two strands read 5′ → 3′ differ (and are not even complementary) ⇒ not palindromes.
Answer: (1)
AIPMT 2012 (Mains)