Question

Eco RI, Eco RV and Sac I are the types of restriction enzymes. Three types of termini can be generated.

(1) 5' staggered ends,

(2) blunt ends, and

(3) 3'staggered ends. Importantly, the 5' termini of each strand in the cleavage product(s) retain the phosphoryl group from the phospho diester bond, the 3' termini are hydroxylated. Here are their actions given.

Which of the following is correct answer?

• A. All of these produce sticky ends.
• B. All of them produce blunt ends.
• C. Each one of them can produce sticky and blunt ends.
• D. All of them act on palindromic sequences.
• E. Both A and D.

Answer 1

The correct option is D All of them act on palindromic sequences.

Each restriction endonuclease recognises a specific palindromic nucleotide sequences in the DNA. The palindrome in DNA is a sequence of base pairs that reads same on the two strands when orientation of reading is kept the same. For example, the following sequences reads the same on the two strands in 5' - 3' direction. 5' GAATTC 3' and 3' CTTAAG 5'. Restriction enzymes cut the strand of DNA a little away from the centre of the palindrome sites, but between the same two bases on the opposite strands. This leaves single stranded portions at the ends. There are overhanging stretches called as sticky ends on each strand.