Question

- Restriction enzymes present in several microorganisms
cut foreign DNA at specific sites and destroy them. The
enzymes do not destroy the cellular DNA because
(a) the cellular DNA does not have the specific sites
(b) the susceptible specific sites are masked by proteins
(c) the restriction enzyme susceptible sites are modified
by cellular enzymes
(d) the restriction enzymes and DNA occupy different
compartments.​

Answer 1

Answer:

The correct option is (B)

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Answer 2

Answer:

Option (c) the restriction enzyme susceptible sites are modified by cellular enzymes

Explanation:

• Restriction endonucleases discovered by Arber in 1962 are the specialized enzymes used in molecular biology. It usually recognizes the short target sequence of about 4 and 8 bps or base pairs.

• Restrictriction enzymes or molecular scissors are very specific to their cleavage function and thus are site-specific. The site recognized by this enzyme is called restriction sites, also present in cellular DNA as well. These restriction sites are typically a palindromic sequence of 4 to 6 nucleotides long where this enzyme makes nicks or cleaves.

• However, cellular enzymes chemically make some modifications to these sites which is why the restriction enzymes fail to recognize them in their DNA. These enzymes become still free to attack and cut the unrestricted recognition sites.  

Hence option (c) is correct.