Question

Differentiate between exonuclease and endonuclease.

Hint:

Endonucleases like restriction enzymes are widely used in genetic engineering to create sticky or blunt ends for DNA ligation.

Answer 1

Step 1: Exonuclease: An exonuclease is an enzyme that removes nucleotides from the ends (either 5’ or 3’) of a DNA or RNA strand.
Step 2: Endonuclease: An endonuclease is an enzyme that cleaves the phosphodiester bonds within the DNA or RNA strand, cutting at specific internal sites.
Step 3: Key Difference: Exonucleases act on the terminal ends of the nucleic acid, while endonucleases cut within the strand. For example, restriction enzymes like EcoRI (seen in the diagram) are endonucleases, cutting at specific recognition sites.
Step 4: Application: Exonucleases are used to remove unwanted nucleotides (e.g., in DNA polishing), while endonucleases are crucial in cloning for cutting DNA at specific sites to insert foreign DNA.
Thus, the primary difference lies in their site of action—ends versus internal regions.