CBSE Class 12-science Answered

(a) Restriction endonucleases are called molecular scissors as they cut the DNA segments at particular locations. Example: EcoRI.

(b) Restriction enzymes cut the DNA strands some distance away from the centre of the palindromic sites, but between the same two bases on the opposite strands. This leaves single stranded portions with overhanging stretches called sticky ends on each strand as they form hydrogen bonds with their complementary cut counterparts. This stickiness at the ends of DNA fragments facilitates the action of enzyme DNA ligase.