Question

Which of the following would be required for the synthesis of rDNA?
(I) Restriction endonuclease
(II) DNA fragments
(III) DNA ligase
(IV) DNA helicase

• A. I, II, IV
• B. I, II, III
• C. I, III, IV
• D. II, III, IV

Answer 1

The correct option is B I, II, III

The technology used for producing recombinant DNA (rDNA) through the combination of DNA molecules from different biological sources that are not normally associated with each other is referred to as recombinant DNA technology.

To create the recombinant DNA, several biological tools such as enzymes as well as DNA from at least two sources are required. For example, a double stranded DNA fragment from a mammal can be taken and introduced into the plasmid DNA isolated from a bacterium.

Following are the steps employed in the creation of rDNA:
Step-1: Isolation of the gene of interest : The gene of interest is amplified, modified by PCR, and eluted from the gel after gel electrophoresis.
Step-2: Cutting the gene at the recognition sites : The DNA from two sources should be cut by the same restriction endonuclease to obtain the complementary sticky ends. These enzymes cut the sugar phosphate backbone in the double stranded DNA at or near specific points called recognition sites that can be palindromic in nature.
Step-3: Ligation of DNA Molecules : The desired DNA fragments with sticky ends are ligated with the help of the enzyme DNA ligase. This results in the formation of recombinant DNA.

Hence, if one has to make an r-DNA, his ideal requirements would be the following: restriction endonucleases, DNA fragments and DNA ligase.

The enzyme DNA helicase is a class of enzymes that unwind the double helical DNA into single strands.