Home Biology Biotechnology Principles and Processes NCERT Two enzymes responsible for restricting the …
Biology Biotechnology Principles and Processes NCERT Single Correct MCQ
Published on: August 14, 2026

Two enzymes responsible for restricting the growth of bacteriophage in E.coli were isolated in 1963, one of these cut DNA, while other :

A
Add propyl group to DNA
B
Add ethyl group to DNA
C
Add methyl group to DNA
D
None of the above

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The correct answer is:
C

In E. coli, two important enzymes involved in restriction-modification system were discovered in 1963:

One enzyme cuts foreign (bacteriophage) DNA → restriction endonuclease

The other enzyme protects host DNA by adding methyl groups (–CH₃) to specific DNA sequences → methylase (methyltransferase)

Methylation prevents the host DNA from being cut by its own restriction enzymes.

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