LIFE SCIENCE

Detailed explanation-1: -Restriction enzymes are found in bacteria (and other prokaryotes). They recognize and bind to specific sequences of DNA, called restriction sites. Each restriction enzyme recognizes just one or a few restriction sites.

Detailed explanation-2: -These enzymes are naturally occurring in bacteria and archaea where they function as an ancient sequence-directed immune system, chopping up phage DNA at restriction sites in the genome of the invading phage.

Detailed explanation-3: -A bacterium uses a restriction enzyme to defend against bacterial viruses called bacteriophages, or phages. When a phage infects a bacterium, it inserts its DNA into the bacterial cell so that it might be replicated. The restriction enzyme prevents replication of the phage DNA by cutting it into many pieces.

Detailed explanation-4: -The discovery of restriction enzymes began with a hypothesis. In the 1960s, Werner Arber observed a dramatic change in the bacteriophage DNA after it invaded these resistant strains of bacteria: It was degraded and cut into pieces.

Detailed explanation-5: -Type I restriction enzymes were the first to be identified and were first identified in two different strains (K-12 and B) of E. coli. These enzymes cut at a site that differs, and is a random distance (at least 1000 bp) away, from their recognition site.