How does a restriction enzyme limit or restrict the effect of a virus on a bacterial cell?
Restriction enzymes restrict foreign DNA by cutting specific palindromic sequences of DNA (palindromic like the name, HANNAH - reads the same both directions). These target sequences are usually 6 nucleotides in length.
Usually the sequences occurs with low abundance in the bacterial cell. A restriction enzyme I used all the time was Sal1 - GTCGAC - and so this sequence would show up 1 out of 4096 bases.
So when I virus invades, it's genome needs to be transcribed and proteins translated. Bacteriophage Lambda is about 48,500 bases in lenght, and so Sal1 would show up approximately 12 times in this genome.
The Sal1 enzyme would keep cutting this genome, and that would disrupt the virus's ability to make new copies of itself.