Question

Restriction enzymes are used to cut:
A. Single stranded RNA
B. Double stranded DNA
C. Single stranded DNA
D. Double stranded RNA

Answer 1

Nucleic acids are large molecules indispensable to all life forms. Nucleic acids are of two types– Deoxy-ribonucleic acid or DNA and Ribonucleic acid or RNA. DNA is composed of two strands that are interlinked with each other, while RNA is a single stranded molecule. There are certain enzymes that can cut these molecules.

Complete answer:
There are two types of Nucleic acid – DNA and RNA. They are made up of three components – sugar, phosphate and a nitrogenous base. There are four types of bases found – Adenine (A), Guanine (G), Cytosine (C), Thymine (T) in DNA, while in RNA, Thymine is replaced by Uracil (U) and other bases remain the same.
Restriction enzymes are a class of enzymes that cleave or cut DNA into fragments. In nature, these enzymes are found in bacteria, as a part of their defense mechanism against viruses that might invade their cells. The restriction enzymes are known to cut the invading DNA into fragments, thereby protecting the host DNA. This process of cutting down a foreign DNA by restriction enzymes is known as Restriction digestion.
The restriction enzymes generally cut DNA at specific sites. They recognize a particular sequence of nucleotides and make a cut in the double stranded DNA. Usually the recognition sites are 4 to 8 base pairs long. Majority of these enzymes recognize palindromic DNA sequences, that is the DNA sequence reads the same both ways and on both the strands.
Restriction enzymes are known to cut double stranded DNA molecules. These enzymes are extremely specific to their target bases. In RNA(s) or in single stranded DNA(s) there is no palindromic site. Also, the RNA contains Uracil base instead of Thymine in DNA. This probably is the reason why restriction enzymes do not act on RNA or in single stranded DNA.
Some examples of restriction enzymes are EcoR1, BamH1, etc.

Therefore, the correct option is (B).

Note:
Restriction enzymes can also be made artificially in the laboratories. Using natural and artificial restriction endonucleases, we can alter the structure of DNA molecules and experiment with gene cloning and protein production. These enzymes can also be used to study DNA length differences among individuals, DNA sequencing and to make DNA libraries.