Question

Assertion: Restriction endonuclease in bacteria protects them from bacteriophages.

Reason: Restriction endonucleases prevent the entry of the bacteriophage DNA.

• A. Both the assertion and reason are false
• B. Both assertion and reason are true and the reason is the correct explanation of the assertion
• C. Both assertion and reason are true but the reason is not the correct explanation of the assertion
• D. The assertion is true but the reason is false

Answer 1

The correct option is D The assertion is true but the reason is false

Restriction endonuclease recognizes specific nucleotide sequences in a DNA molecule, often a palindrome, known as restriction site, and cleaves the DNA at a specific nucleotide within the restriction site. Restriction endonucleases are naturally present in the bacteria where they provide protection against invading bacteriophage DNA.

When a bacteriophage injects its DNA into a bacterium, the restriction enzyme present in the bacterium inspects the length of that DNA sequence and chops off the DNA into fragments. Thus, these enzymes do not prevent entry of the bacteriophage DNA, but inactivate it by breaking it into fragments. So the assertion is true but the reason is false.