The foundations of recombinant DNA technology (rDNA) were laid by the discovery of restriction enzymes. These enzymes are present in many bacteria where they function as part of their defense mechanism called the Restriction Modification system (RM system). Molecular basis of this system was explained first by Werner Arber in 1962. The restriction modification system consists of two components:
(a) A restriction enzyme (called restriction endonuclease) identifies the introduced foreign DNA and cuts it into pieces.
(b) The second component is a modified enzyme (methylase) that adds a methyl group to DNA at specific site to protect it from restriction enzyme cleavage.
Restriction endonucleases are enzymes present in ..(i).. where they function as a part of ..(ii).. mechanism.

Options

A. (i) bacteria (ii) digestive
B. (i) protists (ii) transcription
C. (i) plant cells (ii) replication
D. (i) prokaryotes (ii) defense

Answer

D