Sticky ends are produced by the restriction enzymes. The restriction enzymes cut the strand of DNA a little away from the center of the palindromic sequences but between the same two bases on the opposite strands. This leaves single-stranded portions at the ends. There are overhanging stretches called 'sticky ends' on each strand. These are called sticky ends because they form hydrogen bonds with their complementary cut counterparts. This stickiness of the ends facilitates the action of the enzyme DNA ligase.