Question

Restriction enzymes present in several micro-organisms cut foreign DNA at specific sites and destroy them. These enzymes do not destroy cellular DNA because

• A. cellular DNA does not have the specific sites recognized by these enzymes
• B. the susceptible specific sites are masked by protiens
• C. the restriction enzyme susceptible sites are modified by cellular enzymes
• D. the restriction enzymes and DNA occupy different compartments

Answer 1

The correct option is C the restriction enzyme susceptible sites are modified by cellular enzymes

The restriction enzymes act on certain sites only. These sites are present on the cellular DNA as well. However, cellular enzymes chemically modify these recognition sites making it unrecognizable to the restriction enzyme. The enzymes are still free to attack and cut unrestricted recognition sites.