Question

Identify the DNA segment which is not a palindromic sequence-
A. 5’ GAATTC 3’
     3’ CTTAAG 5’
B. 5’ ÇCCGGG 3’
     3’ GGGCCC 5’
C. 5’ GGATCC 3’
     3’ GGRACC 5’
D. 5’ GCGGCCGC 3’
     3’ CGCCGGCG 5’

Answer 1

Hint: A palindromic sequence is a sequence of nucleic acid in a double-stranded DNA or RNA. The sequence is reading in a certain direction (e.g. 5’ to 3’) on one strand matches the sequence reading in the same direction (e.g.5’ to 3’) on the complementary strand. Therefore the palindromic sequence is dependent on the complementary strands of each other. A nucleotide sequence is known as Palindrome as it is equal to its reverse complement.

Complete answer:
A double helix of a DNA is formed by two paired antiparallel strands of nucleotides that run in the opposite directions. The palindrome sequence is a sequence in which the nucleotides are the same when reading from both directions i.e. antiparallel. The sequence is the same when we read from 5’to3’ and 3’to 5’ direction. In a DNA molecule double helix is formed from the nucleotides that always pair in the manner of - adenine (A) with thymine (T) or uracil(U), cytosine(C) with guanine (G).

 All the above sequences are palindrome sequences as they are the same on reading from both sides. While option C is not a palindrome sequence as it is not the same on reading from the antiparallel direction.

Hence, the correct answer is option (C).

Additional information:
When the order of the base pair changes accidentally then mutation occurs which makes a difference in the production of proteins produced by the base pair. Defects in the DNA repair pathway lead to cancer predisposition.

Note: The sequence of nucleotides shows the degree of complementarity between two nucleic acid strands which determines the stability of the sequence to be together. Many DNA repair and regulatory functions are based on base-pair complementarity. In biotechnology, this concept of complementarity gives rise to the generation of DNA hybrid between RNA and DNA. The human genome is made up of approximately 3 billion base pairs which are essential in forming the helical structure of DNA.