Question

Explain the role of Restriction Endonucleases and Ligases in recombinant DNA technology.

Hint:

Restriction endonucleases act as molecular scissors that cut DNA at specific sequences, while DNA ligases act as molecular glue that join DNA fragments to form recombinant DNA molecules.

Answer 1

Concept: Recombinant DNA (rDNA) technology involves the combination of DNA molecules from different sources to create a new genetic sequence. This process requires specialized enzymes that can cut and join DNA molecules. Two important enzymes used in this technology are restriction endonucleases and DNA ligases. These enzymes help in cutting DNA at specific sites and joining DNA fragments to form recombinant DNA.
Step 1:Role of Restriction Endonucleases.
Restriction endonucleases are enzymes that recognize specific nucleotide sequences in DNA and cut the DNA at those sites.

• These enzymes act as molecular scissors.
• Each restriction enzyme recognizes a specific palindromic sequence in DNA.
• They cut the DNA into fragments with either sticky ends or blunt ends.

For example, the restriction enzyme \textit{EcoRI} recognizes the sequence: \[ GAATTC \] and cuts between the G and A bases, producing sticky ends. These sticky ends are useful because they can easily pair with complementary DNA fragments, allowing foreign DNA to be inserted into a vector.
Step 2:Role of DNA Ligase.
DNA ligase is an enzyme that joins DNA fragments together by forming phosphodiester bonds between adjacent nucleotides.

• It acts as molecular glue.
• DNA ligase seals the nicks in the sugar–phosphate backbone of DNA.
• It joins the foreign DNA fragment with the vector DNA to form recombinant DNA.

This step is essential for creating stable recombinant molecules that can replicate inside host cells.
Step 3:Combined Role in Recombinant DNA Technology.
Both restriction endonucleases and DNA ligases work together in the process of recombinant DNA formation.

• Restriction enzymes cut the donor DNA and vector DNA at specific sites.
• This creates compatible ends that can base-pair with each other.
• DNA ligase then joins these fragments permanently to produce a recombinant DNA molecule.

The recombinant DNA can then be introduced into a host organism, where it replicates and expresses the desired gene.