Question

Which if the following DNA sequences qualify to be designated as a palindrome?
(a)5’ – GACCAG - 3’ in one strand
(b)3’ – GACCAG – 5’ in one strand
(c)5’ – GACGAG – 3’
     3’ – CTGGTC – 5’
(d)5’ – AGCGCT – 3’
     3’ – TCGCGA – 5’

Answer 1

Hint: It is a sequence of nucleic acids within the double helix of DNA and/or RNA that is the same when read from 5' to 3' on one strand and 3' to 5' on the other, complementary. It's also known as an inverted-reverse sequence.

Complete answer:
A palindromic sequence is a sequence of nucleic acids within a double helix of DNA and/or RNA that is the same when read from 5' to 3' on one strand and 5' to 3' on the other, complementary. It is often referred to as a palindrome or an inverted-reverse series. The pairing of nucleotides within the DNA double-helix is complementary, consisting of Adenine (A) pairing with either Thymine (T) in DNA or Uracil (U) in RNA while Cytosine (C) pairs with Guanine (G). So, if the sequence is palindromic, the nucleotide sequence of one strand will be the same as the opposite complementary strand. Endonuclease restriction, Bam HI, binds to and cleaves at a particular cleavage site. As the complementary strand is read backwards, the sequence is 5'-GACCAG-3' which is the same as the first, making it a palindromic sequence.
So, the correct answer is ‘5’ – GACCAG – 3’ in one strand’.

Note: The palindromic series is the same back and forth on both sides. This ensures that the enzyme recognizes the sequence, no matter where the enzyme enters the DNA. A palindromic sequence also raises the probability that both strands of DNA will be cut.