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In 1963, two enzymes responsible for restricting the growth of bacteriophages in Escherichia coli were isolated. One of these enzymes cuts the viral DNA, while the host's own genomic DNA remains unaffected. What is the primary mechanism by which the bacterial host protects its own DNA from being cleaved by this restriction endonuclease?

Options

  1. AThe bacterial chromosome completely lacks the specific palindromic nucleotide sequences recognized by the enzy
  2. BA modifying enzyme adds methyl groups to specific bases within the recognition sites of the host DNA.
  3. CThe restriction enzymes are sequestered within specialized membrane-bound organelles away from the nucleoid.
  4. DThe host DNA is tightly enveloped by a continuous protective protein coat that prevents enzyme binding.

Correct answer

B. A modifying enzyme adds methyl groups to specific bases within the recognition sites of the host DNA.

Step-by-step solution

In 1963, two enzymes responsible for restricting the growth of bacteriophages in Escherichia coli were isolated. This constitutes the restriction-modification system of bacteria. One enzyme is a restriction endonuclease that cuts the viral DNA at specific recognition sites, effectively destroying the bacteriophage. To protect its own genomic DNA from being cleaved by its own restriction enzymes, the bacteria produce a second enzyme (a methylase). This modifying enzyme adds methyl groups to specific bases within the

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