Question

Assertion: A bacterial cell with restriction enzymes will be easily infected and lysed by bacteriophages.
Reason : Restriction enzymes catalyse synthesis of protective coat around bacterial cell that prevents the attack of bacteriophage.

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

Answer 1

The correct option is D Both assertion and reason are false

Restriction enzymes are the endonucleases that cleave the phosphodiester bonds present between the nucleotides within or near to the specific DNA sequences that they identify, called as recognition sites. They are also called ‘molecular scissors’ or ‘biological scissors’ because they cut the DNA and produce fragments.

These restriction enzymes are present in many bacteria as a part of their defence mechanism. The defence mechanism is named “restriction modification system”. It provides defense against foreign DNA such as those from bacteriophages. It consists of two components - restriction enzymes and modification enzymes.

• The restriction enzymes selectively ‘restrict’ the multiplication of the viral/foreign DNA in the cells wherever present, by making several fragments of it.
• The modification enzymes add methyl groups to the bacterial DNA, thus protecting the bacterial DNA from getting cleaved at the recognition sites. This is because the restriction enzymes fail to recognise methylated DNA.

Therefore, both the assertion and reason are also incorrect.