Question

Attempt any TWO of the following: 

With the help of a suitable example illustrate ‘Palindrome’. 

Answer 1

A palindromic sequence is a sequence made up of nucleic acids within 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, strand. It is also known as a palindrome or an inverted-reverse sequence.

The pairing of nucleotides within the DNA double-helix is complementary which consist of Adenine (A) pairing with either Thymine (T) in DNA or Uracil (U) in RNA, while Cytosine (C) pairs with Guanine (G). So if a sequence is palindromic, the nucleotide sequence of one strand would be the same as its reverse complementary strand. An example of a palindromic sequence is 5’-GGATCC-3’, which has a complementary strand, 3’-CCTAGG-5’. This is the sequence where the restriction endonuclease, BamHI, binds to and cleaves at a specific cleavage site. When the complementary strand is read backwards, the sequence is 5’-GGATCC-3’ which is identical to the first one, making it a palindromic sequence.

Another restriction enzyme called EcoR1 recognizes and cleaves the following palindromic sequence:

5’ – G A A T T C – 3’3’ – C T T A A G – 5’