A palindrome in DNA is a sequence of base pairs that reads same on the two strands when orientation of reading is kept the same.
5‘ —— GAATTC —— 3‘
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 sticky ends on each strand which form hydrogen bonds with their complementary cut counterparts & facilitates action of the enzyme DNA ligase.
Restriction endonucleases are used in genetic engineering to form ‘recombinant’ molecules of DNA, which are composed of DNA from different sources/genomes.
When cut by the same restriction enzyme, the resultant DNA fragments have the same kind of ‘sticky-ends’ and, these can be joined together (end-to-end) using DNA ligases.