Which one of the following palindromic base sequences in DNA can be easily cut at about the middle by some particular restriction enzyme?
- 5′ —— CGTTCG —— 3′ 3′ —— ATGGTA —— 5′
- 5′ —— GAATTC —— 3′ 3′ —— CTTAAG —— 5′
- 5′ —— CACGTA —— 3′ 3′ —— CTCAGT —— 5′
- 5′ —— GATATG —— 3′ 3′ —— CTACTA —— 5′
Answer
(2) 5′ —— GAATTC —— 3′ 3′ —— CTTAAG —— 5′
Solution
As per NCERT, a palindrome in DNA is a sequence of base pairs that reads the same on the two strands when the orientation of reading is kept the same (both 5′ → 3′).
⇒ For 5′–GAATTC–3′ / 3′–CTTAAG–5′: the upper strand read 5′ → 3′ is GAATTC and the lower strand read 5′ → 3′ is also GAATTC ⇒ palindrome.
⇒ It is the recognition sequence of EcoRI, which cuts each strand between G and A, a little away from the centre, leaving sticky ends.
⇒ The other sequences do not read the same on both strands (in (1), (3) and (4) the strands are not even fully complementary).
Answer: (2)