What do restriction endonucleases do -

Ans. is 'a' i.e., Cut ds dna at specific sites o Endonucleases-enzymes that cut DNA at specific DNA sequences within the molecule (as opposed to exonucleases, which digest from the ends of DNA molecules)-are a key tool in recombinant DNA research,o These enzymes were called restriction enzymes because their presence in a given bacterium restricted the growth of certain bacterial viruses called bacteriophages.o Restriction enzymes cut DNA of any source into short pieces in a sequence-specific manner-in contrast to most other enzymatic, chemical, or physical methods, which break DNA randomly.o Restriction endonucleases cleave (cut) both strands of DNAQ.o Some restriction enzymes cut both strand at same level, so as to leave no unpaired bases on either end.o These ends are called blunt endsQ.o On the other hand, some restriction enzyme cut two strands in staggered manner, leaving two to four nucleotides of one strand unpaired at each end.o Thses ends are referred to as cohesive ends (or sticky ends42 or staggered ends).