Which one of the following represents a palindromic sequence?

The correct answer is Option (1) → 5'-GAATTC-3'   3'-CTTAAG-5'

To test a palindrome, read the top strand 5′→3′ and the bottom strand also 5′→3′, that is, the bottom strand from right to left. The two readings must be the same.

Option (1) — Correct. Top: GAATTC. Bottom read from its 5′ end: GAATTC. The same on both strands; this is the site of EcoRI.

Option (2) — Incorrect. Top: CCAATG. Bottom read from its 5′ end: CCTAAG. The two differ. (The strands are not even fully complementary.)

Option (3) — Incorrect. Top: CATTAG. Bottom read from its 5′ end: CAATAG. The two differ.

Option (4) — Incorrect. Top: GATACC. Bottom read from its 5′ end: GAATCC. The two differ.

Note: A similar question was also asked in CUET (UG) 2026 on 14-05-2026 (Slot 2).

NCERT Extract:
Restriction Enzymes – “Each restriction endonuclease functions by ‘inspecting’ the length of a DNA sequence. Once it finds its specific recognition sequence, it will bind to the DNA and cut each of the two strands of the double helix at specific points in their sugar-phosphate backbones (Figure 9.1). Each restriction endonuclease recognises a specific palindromic nucleotide sequences in the DNA. … These are groups of letters that form the same words when read both forward and backward, e.g., “MALAYALAM”. As against a word-palindrome where the same word is read in both directions, the palindrome in DNA is a sequence of base pairs that reads same on the two strands when orientation of reading is kept the same. For example, the following sequences reads the same on the two strands in 5’ → 3’ direction. This is also true if read in the 3’ → 5’ direction.”
5’ —— GAATTC —— 3’
3’ —— CTTAAG —— 5’