A restriction endonuclease is used in genetic engineering to
- A. cut DNA at a specific base sequence, often leaving sticky ends
- B. join two DNA fragments together
- C. translate mRNA into protein
- D. unwind the double helix during replication
Explanation
Each enzyme recognises its own short palindromic sequence and cuts both strands there, and a staggered cut leaves short single stranded overhangs. Because the same enzyme produces complementary overhangs on the gene and on the plasmid, the two pair up by hydrogen bonding when mixed. Bacteria evolved these enzymes as a defence against phage DNA.