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Which one of the following represents a palindromic sequence in DNA?
A
5′ - GATACC - 3′ / 3′ - CCTAAG - 5′
B
5′ - GAATTC - 3′ / 3′ - CTTAAG - 5′
C
5′ - CCAATG - 3′ / 3′ - GAATCC - 5′
D
5′ - CATTAG - 3′ / 3′ - GATAAC - 5′
Detailed Solution
A palindromic sequence 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 (5′ → 3′ on both strands).
Take 5′ - GAATTC - 3′ with its complementary strand 3′ - CTTAAG - 5′.
Reading the upper strand 5′ → 3′ gives GAATTC; reading the lower strand 5′ → 3′ also gives GAATTC.
This is the recognition sequence of the restriction enzyme EcoRI.
In the other sequences the two strands are not even proper complements of each other and they do not read the same in the 5′ → 3′ direction.
Hence the palindromic sequence is 5′ - GAATTC - 3′ / 3′ - CTTAAG - 5′.
Take 5′ - GAATTC - 3′ with its complementary strand 3′ - CTTAAG - 5′.
Reading the upper strand 5′ → 3′ gives GAATTC; reading the lower strand 5′ → 3′ also gives GAATTC.
This is the recognition sequence of the restriction enzyme EcoRI.
In the other sequences the two strands are not even proper complements of each other and they do not read the same in the 5′ → 3′ direction.
Hence the palindromic sequence is 5′ - GAATTC - 3′ / 3′ - CTTAAG - 5′.