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, so it is a 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)