But these are specified by genes, and genes can mutate. In population, will always find some variant strains with slightly different cell surfaces, may not bind virus well. When phage first discovered, thought this could be effective weapon against bacterial disease. But frequency of resistant bacterial strains was too high, any given strain of virus quickly became useless as resistant survivors propagated. Exoenzymes attack free 5' or 3' ends of DNA, RNA molecules.
Endonucleases are potentially lethal weapons.
Called restriction enzymes . Because cell also has a second enzyme, called modification enzyme , that protects all host DNA sequences of this type. The methylated base is modified, and protected from the restriction enzyme. The importance of Restriction Enzymes Restriction enzymes are responsible for the genetic revolution. They make reproducible, specific cuts with surgical precision.