The complementary DNA sequence of the DNA strand 5'-GAATTC-3' would b…

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

A pairs with T and G with C, and the partner strand runs the opposite way: 5′ GAATTC 3′ pairs with 3′ CTTAAG 5′.

Option (1) 3'-GAATTC-5' — Incorrect. It repeats the bases instead of pairing them.

Option (2) 5'-CTTAAG-3' — Incorrect. The bases are right, but the strand runs 3′ to 5′.

Option (3) 3'-CTTAAG-5' — Correct. In DNA, A pairs with T and G pairs with C, and the two strands run antiparallel. So the strand complementary to 5′-GAATTC-3′ is 3′-CTTAAG-5′, read base by base against the given strand.

Option (4) 3'-CTTUUG-5' — Incorrect. DNA has T, not U.

Note: A similar question was also asked in CUET (UG) 2023 on 22-05-2023 (Slot 1).

NCERT Extract:
Restriction Enzymes – “… Each restriction endonuclease recognises a specific palindromic nucleotide sequences in the DNA.”
Restriction Enzymes – “… 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’”