Question

Which of the following restriction enzymes produces blunt ends?
A. Sal Ⅰ
B. Eco RV
C. Xho Ⅰ
D. Hind Ⅲ

Answer 1

Hint: Protein molecules that influence a reaction to give specific products are called enzymes. The enzymes act on the substrate, break it down or convert it into the end product. Certain bacterial enzymes can cut the DNA at specific sites. These enzymes are called restriction enzymes or endonucleases. This property of the restriction enzyme is used in recombinant DNA technology.

Complete answer:
When a foreign DNA enters the bacterial cell, the restriction enzyme recognizes specific sites called the restriction sites in the foreign DNA. It will cut the DNA at these sites rendering the foreign DNA inactive. The restriction enzyme does not cleave the bacterial DNA, thereby protecting itself.
Quite a few of these restriction enzymes recognize palindromic sequences on the DNA. Palindromic sequences are certain nucleotide sequences in a double-stranded DNA molecule that reads the same in $$5^{\prime }-3^{\prime }$$direction and $3^{\prime }-5^{\prime }$direction.
When the restriction enzyme cuts the DNA in such a way that it leaves nucleotide overhangs (uneven ends), these ends are called sticky ends. As the same restriction enzyme cuts the DNA strands both the strands have the same overhangs.
When no overhangs are produced after the restriction enzymes act on the DNA, the ends are called blunt ends. Restriction enzymes are of four types, out of which three can cleave DNA molecules.
SalⅠ recognizes $5^{\prime }-GTCGAC-3^{\prime }$ sequence on the DNA cleaves the DNA to produce $5^{\prime }$overhangs ( $5^{\prime }-C$).
Eco RⅤ recognizes $5^{\prime }-GATATC-3^{\prime }$ and its complementary strand. It cleaves the DNA right in the middle of the sequence. The DNA has blunt ends (no uneven ends/overhangs).
XhoⅠ recognizes $5^{\prime }-CTCGAG-3^{\prime }$and its complementary strand. It produces $5^{\prime }$overhangs ($5^{\prime }-C$).
Hind Ⅲ recognizes $5^{\prime }-AAGCTT-3^{\prime }$ and it’s complementary and produces $5^{\prime }$overhangs ($5^{\prime }-A$).

Hence, the correct answer is option (B).

Note: Restriction enzymes also perform another function i.e. modification of the DNA molecule. They can introduce molecules such as methyl groups to the DNA to modify it. The type four restriction enzymes can modify the DNA.
These enzymes can be isolated from bacterial cells and be used to create specific DNA segments that can be inserted into vectors. These vectors can be introduced into any other organism that will now express characteristics of the segmented DNA. Therefore, the restriction enzymes can be used for cloning or in recombinant DNA technology.