CBSE Class 12-science Answered

Special sequences in the DNA recognised by restriction endonucleases are called palindromic nucleotide sequences. The palindromes in DNA are base pair sequences that are same when read forward or backward from a central axis of symmetry.

Restriction enzymes cut the strand of DNA a little away from the centre of the palindrome sites but between the same two bases of the opposite strands. This leaves single stranded unpaired bases at cut ends so that they form hydrogen bonds with their complementary cut counter parts. These cut ends with unpaired bases are called sticky ends or cohesive ends. The sticky ends facilitate the action of enzyme DNA ligase.