The role of restriction enzyme in recombinant DNA technology is:

The correct answer is Option (3) → Cutting DNA at specific point

Option (1) Join sticky ends of DNA strand — Incorrect. Joining sticky ends is done by DNA ligase, not by restriction enzymes. Restriction enzymes only cut the DNA.

Option (2) Make cut in RNA strand — Incorrect. Restriction enzymes cut DNA, not RNA, at specific recognition sequences.

Option (3) Cutting DNA at specific point — Correct. Restriction enzymes recognise a specific palindromic recognition sequence and cut DNA at a specific point in it. This lets the same enzyme cut the vector and the foreign DNA so they can be joined.

Option (4) Joining and Cutting of RNA strand — Incorrect. Restriction enzymes neither cut nor join RNA. They cut DNA at specific points; joining is done by DNA ligase.

NCERT Extract:
Restriction Enzymes – “… Each restriction endonuclease functions by ‘inspecting’ the length of a DNA sequence. Once it finds its specific recognition sequence, it will bind to the DNA and cut each of the two strands of the double helix at specific points in their sugar-phosphate backbones (Figure 9.1).”