Question

Which one of the following represents a palindromic sequence in DNA?
A. 5’ CCAATG 3’
   3’ GAATTC 5’
B. 5’ CATTAG 3’
   3’ GATAAC 5’
C. 5’ GATACC 3’
   3’ CCTAAG 5’
D. 5’ GAATTC 3’
   3’ CTTAAG 5’

Answer 1

Hint: Some Sequences present in DNA read the same in the DNA strand and complementary strand. The sequence is the same when both strands read from 5’ to 3’.

Complete Answer:
A palindrome is a word that reads alike forward and backward e.g. madam, rotor. The base sequence of both the strands when read from 5’ to 3’or vice-versa are the same. For Example:
5’ CATGCTGA………………….. 3’
3’………………… AGTCGTAC 5’
The process of transcription stops by termination signals. Two types of termination are identified.

1. Rho-dependent termination: A specific protein, named rho factor, binds to the growing RNA (and not to RNA polymerase) or weakly to DNA, and in the bound state it acts as ATPase and terminates transcription and releases RNA. The rho factor is also responsible for the dissociation of RNA polymerase from DNA.

2. Rho-independent termination: The termination, in this case, is brought about by the formation of hairpins of newly synthesized RNA. It takes place due to the presence of palindromes. The presence of palindromes in the base sequence of the DNA template (same when read in opposite direction) in the termination region is known. As a result of this, the newly synthesized RNA folds to form a hairpin-like structure (due to complementary base pairing) that causes termination of transcription.

So, the correct answer is D.

Note: Restriction enzyme identify and cut specific sites of palindromic sequence which are also known as restriction sites. This is an important step in the process of DNA replication.