What is the normal role of restriction endonucleases in bacterial cells?

ANS:B - To degrade invading phage DNA

Option A) violates the significance of replication. Broken pieces of DNA ceases replication process if not ligated quickly.

Option C) also incorrect because RNA primers are synthesized by primase and not by res. Endonucleases and so it is obvious that option D) can also be ruled out.

Option B) is correct because the biological role of these enzymes is in restriction-modification (R-M) systems that have evolved to cleave the bacteriophage DNA injected into the cell and thus act as a defence mechanism against phage infection.