Question

The word ‘restriction’ in restriction enzyme refers to

• A. Cleaving of phosphodiester linkage
• B. Cutting of DNA at specific position only
• C. All of the above
• D. Prevention of the multiplication of bacteriophage in
  bacteria

Answer 1

The correct option is D Prevention of the multiplication of bacteriophage in

bacteria
Restriction endonuclease
Restriction endonucleases are the enzymes which cleave the DNA by digesting phosphodiester bonds at the specific sequences within the DNA. Examples include $Eco$R I and $Hind$ II.

Restriction modification system
Restriction modification system is a defence mechanism in bacteria, which is used against bacteriophages. It consists of two enzymes that work in the following manner:
1)Restriction enzyme : They restrict the propagation of foreign DNA in the bacterium. Hence the word ‘restriction’ in restriction enzyme refers to prevention of the multiplication of bacteriophages in bacteria.
2)Modification enzyme : They add methyl groups to one or more bases within the recognition sequence of restriction enzymes. The DNA with the modified sequences cannot be recognised and cut by restriction enzymes.

Final answer
(C) Prevention of the multiplication of bacteriophage in bacteria